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| 2. |
- Aminifar, Amir, et al.
(författare)
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Control-Quality Driven Design of Embedded Control Systems with Stability Guarantees
- 2018
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Ingår i: IEEE Design and Test. - : IEEE. - 2168-2356 .- 2168-2364. ; 35:4, s. 38-46
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Tidskriftsartikel (refereegranskat)abstract
- Today, the majority of control applications in embedded systems, e.g., in the automotive domain, are implemented as software tasks on shared platforms. Ignoring implementation impacts during the design of embedded control systems results in complex timing behaviors that may lead to poor performance and, in the worst case, instability of control applications. This article presents a methodology for implementation-aware design of high-quality and stable embedded control systems on shared platforms with complex timing behaviors.
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| 3. |
- Barzegaran, Mohammadreza, et al.
(författare)
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Towards quality-of-control-aware scheduling of industrial applications on fog computing platforms
- 2019
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Ingår i: IoT-Fog 2019 - Proceedings of the 2019 Workshop on Fog Computing and the IoT. - New York, NY, USA : ACM. - 9781450366984 ; , s. 1-5
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Konferensbidrag (refereegranskat)abstract
- In this paper we address Industrial IoT control applications which are safety-critical and real-time, and which have very low latency and jitter requirements. These control applications are virtualized as software tasks running on a Fog Computing Platform that brings computing and deterministic communication closer to the edge of the network, where the industrial "things" are located. Due to the demanding dependability and timing requirements, we consider that the tasks are scheduled with a static-cyclic scheduling policy. We are interested to determine the mapping of the tasks and a schedule table of their activation, such that we maximize the quality-of-control for the control tasks and meet the timing requirements for all tasks, including non-critical real-time tasks. We have proposed a Simulated Annealing-based metaheuristic to solve this problem, and we have evaluated the solution on several test cases.
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| 4. |
- Cederqvist, L, et al.
(författare)
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Improved Temperature and Depth Control During FSW of Copper Canisters Using Feedforward Compensation
- 2016
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Ingår i: Friction Stir Welding and Processing VIII. - Hoboken, NJ, USA : John Wiley & Sons, Inc.. - 9781119082491 ; , s. 69-76
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Konferensbidrag (refereegranskat)abstract
- The welding procedure to seal copper canisters requires variable power input throughout the 45 minute long weld cycle to keep the probe temperature within the process window. By using a cascaded loop that determines the power input requirement, the controller will not be dependent on repeatability in the necessary power input between weld cycles, and the lag time in the probe temperature measurement will not be critical. Due to fast-changing thermal boundary conditions during the downward sequence, a feedforward to the power input was designed to further improve controller performance. In addition to the cascade controller adjusting the tool rotation rate, a depth controller is adjusting the axial force to control the shoulder depth. The purpose is to eliminate flash due to excessive shoulder depth and to control the position of the probe tip, which influeces the size and shape of the hook defect produced. Controlling depth is challenging for several reasons, including deflection in the welding machine and thermal expansion of the weld material, and also results in cross-coupling between axial force and spindle torque. The cross-coupling was handled by another feedforward compensator that adjusts the tool rotation rate based on the commanded axial force. The implemented controllers and feedforward compensators have been evaluated over several welds with good results, where the depth is kept within ±0.1mm when the tool reaches the joint line sequence and the probe temperature is held within ±5°C during full circumferential welds compared to a process window of ±60°C.
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| 5. |
- Cervin, Anton
(författare)
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Event-Based Control and Estimation of Server Systems
- 2018
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Ingår i: Proceedings of the 4th International Conference on Event-Based Control, Communication, and Signal Processing, EBCCSP 2018.
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Konferensbidrag (refereegranskat)abstract
- Feedback control is increasingly being applied in server systems to make them more robust and efficient. This includes managing quality of service, minimizing power consumption, and adapting to varying workloads. Successful adaptation and control in turn relies on accurate tracking of workload variations and timely detection of changes in the computing infrastructure. Given that server systems are inherently event based, it is natural to consider event-based control and estimation schemes for them. As a prototypical problem, we study a single server system with time-varying arrival rate and derive optimal switching rules for the service rate. The goal is to keep the response time within bounds while minimizing the energy consumption of the server. We also design an event-based estimator of the server states using a particle filter approach. Finally, we outline some research challenges related to event-based control and information fusion in server systems.
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| 6. |
- Cervin, Anton
(författare)
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JitterTime 1.0—Reference Manual
- 2019
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This technical report describes JitterTime, a Matlab toolbox for calculating the time-varying state covariance of a mixed continuous/discrete linear system driven by white noise. It also integrates a quadratic cost function for the system. The passing of time and the updating of the discrete-time systems are explicitly managed by the user in a simulation run. Since the timing is completely handled by the user, any complex timing scenario can be analyzed, including scheduling algorithms, timing jitter and drift, and asynchronous execution in distributed systems. Some examples of how the toolbox can be used to evaluate the control performance of time-varying systems are given.
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| 7. |
- Cervin, Anton
(författare)
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LQG-optimal PI and PID control as benchmarks for event-based control
- 2016
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Ingår i: 2016 2nd International Conference on Event-Based Control, Communication, and Signal Processing, EBCCSP 2016 - Proceedings. - 9781509041961
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Konferensbidrag (refereegranskat)abstract
- We formulate two simple benchmark problems for event-based control, where the optimal solutions in the continuous-time setting turn out to be ordinary PI and PID controllers. The benchmarks can be used to compare the performance of continuous-time, discrete-time, and various event-based controllers with regard to for instance disturbance attenuation, control effort, and average sampling or actuation rates. They can also be used to evaluate heuristic event-based PI(D) controllers and see how their performance compare to each other and to regular sampled-data control. We give two benchmark examples, where we study the trade-off between event frequency and regulator performance for a number of previously proposed approaches to event-based control.
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| 8. |
- Cervin, Anton, et al.
(författare)
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TrueTime : Simulation Tool for Performance Analysis of Real-Time Embedded Systems
- 2018
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Ingår i: Model-Based Design for Embedded Systems. - : CRC Press. - 9781420067842 - 9781420067859 ; , s. 145-176
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Bokkapitel (refereegranskat)abstract
- Embedded systems and networked embedded systems play an increasingly important role in today’s society. They are often found in consumer products (e.g., in automotive systems and cellular phones), and are therefore subject to hard economic constraints. The pervasive nature of these systems generates further constraints on physical size and power consumption. These product-level constraints give rise to resource constraints on the implementation platform, for example, limitations on the computing speed, memory size, and communication bandwidth. Because of economic considerations, this is true in spite of the rapid hardware development. In many applications, using a processor with a larger capacity than strictly necessary cannot be justified.
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| 9. |
- Cervin, Anton, et al.
(författare)
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Using JitterTime to Analyze Transient Performance in Adaptive and Reconfigurable Control Systems
- 2019
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Ingår i: 2019 24th IEEE International Conference on Emerging Technologies and Factory Automation (ETFA). - 9781728103037 - 9781728103020 - 9781728103044
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Konferensbidrag (refereegranskat)abstract
- This paper presents JitterTime, a small Matlab toolbox for calculating the transient performance of a control system in non-ideal timing scenarios. Such scenarios arise in networked and embedded systems, where several applications share a set of limited and varying resources. Technically, the toolbox evaluates the time-varying state covariance of a mixed continuous/discrete linear system driven by white noise. It also integrates a quadratic cost function for the system. The passing of time and the updating of the discrete-time systems are explicitly managed by the user in a simulation run. Since the timing is completely handled by the user, any complex timing scenario can be analyzed, including adaptive scheduling and reconfiguration between different system modes. Three examples of how the toolbox can be used to evaluate the control performance of such time-varying systems are given.
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| 10. |
- Khalilzad, Nima
(författare)
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Adaptive and Flexible Scheduling Frameworks for Component-Based Real-Time Systems
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Modern computer systems are often designed to play a multipurpose role. Therefore, they are capable of running a number of software components (software programs) simultaneously in parallel. These software components should share the system resources (e.g. processor and network) such that all of them run and finish their computations as expected. On the other hand, a number of software components have timing requirements meaning that they should not only access the resources, but this access should also be in a timely manner. Thus, there is a need to timely share the resources among different software components. The time-sharing is often realized by reserving a time-portion of resources for each component. Such a reservation should be adequate and resource-efficient. It should be sufficient to preserve the timing properties of the components. Also, the reservations should be resource-efficient to reduce the components' footprint on the resources which in turn allows integration of more software components on a given hardware resource. In this thesis, we mainly focus on the resource-efficiency of the reservations. We consider two cases. (I) Components which can tolerate occasional timing violations (soft real-time components): in this case we adjust the reservations during run-time to match the reservation sizes based on the instantaneous requirements of the components. (II) Components which cannot tolerate any timing violations (hard real-time components): in this case we use flexible approaches which allow us to improve the resource-efficiency at the design time.
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