| 1. |
- Andersson, Martin, et al.
(författare)
-
Co-simulation of Mobile Wireless Networked Embedded Systems in Physical Environments
- 2005
-
Ingår i: RTiS 2005 – Proceedings of Real Time in Sweden 2005, the 8th Biennial SNART Conference on Real-Time Systems (Skövde University Studies in Informatics). - 1653-2325. - 9163173492 ; 2005:1
-
Konferensbidrag (refereegranskat)abstract
- Embedded systems are becoming increasingly networked and aredeployed in application areas that require close interaction withtheir physical environment. Examples include distributed mobileagents and wireless sensor/actuator networks. The complexity ofthese applications make co-simulation a necessary tool during systemdevelopment. This paper presents a simulation environment thatfacilitates simulation of computer nodes and communication networksinteracting with the continuous-time dynamics of the real world.Features of the simulator include interrupthandling, task scheduling, wired and wireless communication, localclocks, dynamic voltage scaling, and battery-driven operation.Two simulation case studies are presented: a simple communicationscenario and a mobile robot soccer game.
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| 2. |
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| 3. |
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| 4. |
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| 5. |
- Aminifar, Amir, et al.
(författare)
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Control-Quality Driven Design of Cyber-Physical Systems with Robustness Guarantees
- 2013
-
Ingår i: Design, Automation & Test in Europe (DATE 2013). - : IEEE. - 1530-1591. - 9781467350716 ; , s. 1093-1098
-
Konferensbidrag (refereegranskat)abstract
- Many cyber-physical systems comprise several control applications sharing communication and computation resources. The design of such systems requires special attention due to the complex timing behavior that can lead to poor control quality or even instability. The two main requirements of control applications are: (1) robustness and, in particular, stability and (2) high control quality. Although it is essential to guarantee stability and provide a certain degree of robustness even in the worst-case scenario, a design procedure which merely takes the worst-case scenario into consideration can lead to a poor expected (average-case) control quality, since the design is solely tuned to a scenario that occurs very rarely. On the other hand, considering only the expected quality of control does not necessarily provide robustness and stability in the worst-case. Therefore, both the robustness and the expected control quality should be taken into account in the design process. This paper presents an efficient and integrated approach for designing high-quality cyber-physical systems with robustness guarantees.
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| 6. |
- Aminifar, Amir, et al.
(författare)
-
Control-Quality Driven Design of Embedded Control Systems with Stability Guarantees
- 2018
-
Ingår i: IEEE Design and Test. - : IEEE. - 2168-2356 .- 2168-2364. ; 35:4, s. 38-46
-
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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| 7. |
- Aminifar, Amir, et al.
(författare)
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Designing High-Quality Embedded Control Systems with Guaranteed Stability
- 2012
-
Ingår i: 33rd IEEE Real-Time Systems Symposium (RTSS 2012. - 1052-8725. - 9781467330985
-
Konferensbidrag (refereegranskat)abstract
- Many embedded systems comprise several controllers sharing available resources. It is well known that such resource sharing leads to complex timing behavior that degrades the quality of control, and more importantly, can jeopardize stability in the worst-case, if not properly taken into account during design. Although stability of the control applications is absolutely essential, a design flow driven by the worst-case scenario often leads to poor control quality due to the significant amount of pessimism involved and the fact that the worst-case scenario occurs very rarely. On the other hand, designing the system merely based on control quality, determined by the expected (average-case) behavior, does not guarantee the stability of control applications in the worst-case. Therefore, both control quality and worst-case stability have to be considered during the design process, i.e., period assignment, task scheduling, and control-synthesis. In this paper, we present an integrated approach for designing high-quality embedded control systems, while guaranteeing their stability.
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| 8. |
- Aminifar, Amir, et al.
(författare)
-
Stability-Aware Analysis and Design of Embedded Control Systems
- 2013
-
Ingår i: Proceedings of the International Conference on Embedded Software (EMSOFT), 2013. - : IEEE conference proceedings. - 9781479914432 - 9781479914425 ; , s. 1-10
-
Konferensbidrag (refereegranskat)abstract
- Many embedded systems comprise several controllers sharing available resources. It is well known that such resource sharing leads to complex timing behavior that can jeopardize stability of control applications, if it is not properly taken into account in the design process, e.g., mapping and scheduling. As opposed to hard real-time systems where meeting the deadline is a critical requirement, control applications do not enforce hard deadlines. Therefore, the traditional real-time analysis approaches are not readily applicable to control applications. Rather, in the context of control applications, stability is often the main requirement to be guaranteed, and can be expressed as the amount of delay and jitter a control application can tolerate. The nominal delay and response-time jitter can be regarded as the two main factors which relate the real-time aspects of a system to control performance and stability. Therefore, it is important to analyze the impact of variations in scheduling parameters, i.e., period and priority, on the nominal delay and response-time jitter and, ultimately, on stability. Based on such an analysis, we address, in this paper, priority assignment and sensitivity analysis problems for control applications considering stability as the main requirement.
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| 9. |
- Andersson, Martin, et al.
(författare)
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Simulation of Wireless Networked Control Systems
- 2005
-
Ingår i: Proceedings of the 44th IEEE Conference on Decision and Control and the 2005 European Control Conference. - 0780395689 ; , s. 476-481
-
Konferensbidrag (refereegranskat)abstract
- Embedded systems are becoming increasingly networked and are deployed in application areas that require close interaction with their physical environment. Examples include distributed mobile agents and wireless sensor/actuator networks. The complexity of these applications make co-simulation a necessary tool during system development. This paper presents a simulation environment that facilitates simulation of computer nodes and communication networks interacting with the continuous-time dynamics of the real world. Features of the simulator include interrupt handling, task scheduling, wired and wireless communication, local clocks, dynamic voltage scaling, and battery-driven operation. Two simulation case studies are presented: a simple communication scenario and a mobile robot soccer game.
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| 10. |
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| 11. |
- Araujo, Jose, 1985-
(författare)
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Design and Implementation of Resource-Aware Wireless Networked Control Systems
- 2011
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Networked control over wireless sensor and actuator systems is of growing importancein many application domains. Energy and communication bandwidth are scarce resources in such systems. Despite that feedback control might only be needed occasionally, sensor and actuator communications are often periodic and with high frequency in today’s implementations. In this thesis, resource-constrained wireless networked control systems with an adaptive sampling period are considered. Our first contribution is a system architecture for aperiodic wireless networked control. As the underlying data transmission is performed over a shared wireless network, we identify scheduling policies and medium access controls that allow for an efficient implementation of sensor communication. We experimentally validate three proposed mechanisms and show that best performance is obtained by a hybrid scheme, combining the advantages of event- and self-triggered control as well as the possibilities provided by contention-based and contention-free medium accesscontrol. In the second contribution, we propose an event-triggered PI controller for wireless process control systems. A novel triggering mechanism which decides the transmission instants based on an estimate of the control signal is proposed. It addresses some side-effects that have been discovered in previous PI proposals, which trigger on the state of the process. Through simulations we demonstrate that the new PI controller provides setpoint tracking and disturbance rejection close to a periodic PI controller, while reducing the required network resources. The third contribution proposes a co-design of feedback controllers and wireless medium access. The co-design is formulated as a constrained optimization problem, whereby the objective function is the energy consumption of the network and the constraints are the packet loss probability and delay, which are derived from the performance requirements of the control systems. The design framework is illustrated in a numerical example.
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| 12. |
- Barzegaran, Mohammadreza, et al.
(författare)
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Performance Optimization of Control Applications on Fog Computing Platforms Using Scheduling and Isolation
- 2020
-
Ingår i: IEEE Access. - 2169-3536. ; 8, s. 104085-104098
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper, we address mixed-criticality applications characterized by their safety criticality and time-dependent performance, which are virtualized on a Fog Computing Platform (FCP). The FCP is implemented as a set of interconnected multicore computing nodes, and brings computation and communication closer to the edge of the network, where the machines are located in industrial applications. We use partitioning and static-cyclic scheduling to provide isolation among mixed-criticality tasks and to guarantee their timing requirements. The temporal and spatial isolation is enforced via partitions, which execute tasks with the same criticality level. We consider that the tasks are scheduled using static cyclic scheduling. We are interested in determining the mapping of tasks to the cores of the fog nodes, the assignment of tasks to the partitions, the partition schedule tables, and the tasks’ schedule tables, such that the Quality-of-Control for the control tasks is maximized and we meet the timing requirements for all tasks, including tasks with lower-criticality levels. We are also interested in determining the periods for control tasks to balance the schedulability and the control performance. We have proposed a Simulated Annealing metaheuristic, which relies on a heuristic algorithm for determining the schedules and partitions, to solve this optimization problem. Our optimization strategy has been evaluated on several test cases, showing the effectiveness of the proposed method.
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| 13. |
- Barzegaran, Mohammadreza, et al.
(författare)
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Towards quality-of-control-aware scheduling of industrial applications on fog computing platforms
- 2019
-
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
-
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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| 14. |
- Bate, Iain, et al.
(författare)
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Establishing Timing Requirements and Control Attributes for Control Loops in Real-Time Systems
- 2003
-
Ingår i: Proceedings 15th Euromicro Conference on Real-Time Systems, 2003.. - 0769519369 ; , s. 121-128
-
Konferensbidrag (refereegranskat)abstract
- Advances in scheduling theory have given designers of control systems greater flexibility over their choice of timing requirements. This could lead to systems becoming more responsive and more maintainable. However, experience has shown that engineers find it difficult to exploit these advantages due to the difficulty in determining the “real” timing requirements of systems and therefore the techniques have delivered less benefit than expected. Part of the reason for this is that the models used by engineers when developing systems do not allow for emergent properties such as timing. This paper presents an approach and framework for addressing the problem of identifying an appropriate and valid set of timing requirements and their corresponding control parameters.
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| 15. |
- Bini, Enrico, et al.
(författare)
-
Delay-Aware Period Assignment in Control Systems
- 2008
-
Konferensbidrag (refereegranskat)abstract
- We consider the problem of optimal static period assignment for multiple independent control tasks executing on the same CPU. Previous works have assumed that the control performance can be expressed as a function of the sampling rate only. Arguing that the control delay has a large impact on the control performance, in this work we include the control delay in the cost function. The delay is estimated using an approximate response-time analysis. Assuming linear cost functions for the controllers then allows us to solve the optimal period assignment problem analytically. The performance improvements over previous methods are verified in evaluations on synthetic task sets as well as detailed co-simulations of the controllers, the plants, and the scheduler.
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| 16. |
- Buttazzo, Giorgio, et al.
(författare)
-
Comparative Assessment and Evaluation of Jitter Control Methods
- 2007
-
Konferensbidrag (refereegranskat)abstract
- Most control systems involve the execution of periodic activities, which are automatically activated by the operating system at the specified rates. When the application consists of many concurrent tasks, each control activity may experience delay and jitter, which depend on several factors, including the scheduling algorithm running in the kernel, the overall workload, the task parameters, and the task interactions. If not properly taken into account, delays and jitter may degrade the performance of the system and even jeopardize its stability. In this paper, we evaluate three methodologies for reducing the jitter in control tasks: the first one consists of forcing the execution of inputs and outputs at the period boundaries, so trading jitter with delay; the second method reduces jitter and delay by assigning tasks shorter deadlines; whereas, the third method relies on non preemptive execution. We compare these techniques by illustrating examples, pointing out advantages and disadvantages, and evaluating their effects in control applications by simulation. It is found that the deadline advancement method gives the better control performance for most configurations.
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| 17. |
- Castañé, Rosa, et al.
(författare)
-
Resource Management for Control Tasks Based on the Transient Dynamics of Closed-Loop Systems
- 2006
-
Konferensbidrag (refereegranskat)abstract
- This paper presents a resource management strategy for control tasks that maximizes control performance within the available resources by readjusting the task periods at run-time. A feedback scheduler is used to determine on-line the optimal task periods considering the response over a finite time horizon of the plants controlled by arbitrary linear control laws. We show how this problem can be expressed as an optimization problem, where the objective function relates the sampling periods to the transient responses of the controlled plants, and where restrictions are based on EDF schedulability constraints. For the general case, the solution of the optimization problem is computationally expensive, and thus, an approximate procedure to be executed on-line has been developed. We present simulation results that validate the presented approach.
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| 18. |
- Cava, José Manuel Gonzáles, et al.
(författare)
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Robust PID control of propofol anaesthesia: uncertainty limits performance, not PID structure
- 2021
-
Ingår i: Computer Methods and Programs in Biomedicine. - : Elsevier BV. - 0169-2607. ; 198, s. 1-1
-
Tidskriftsartikel (refereegranskat)abstract
- Background and objective: New proposals to improve the regulation of hypnosis in anaesthesia based on the development of advanced control structures emerge continuously. However, a fair study to analyse the real benefits of these structures compared to simpler clinically validated PID-based solutions has not been presented so far. The main objective of this work is to analyse the performance limitations associated with using a filtered PID controller, as compared to a high-order controller, represented through a Youla parameter.Methods: The comparison consists of a two-steps methodology. First, two robust optimal filtered PID controllers, considering the effect of the inter-patient variability, are synthesised. A set of 47 validated paediatric pharmacological models, identified from clinical data, is used to this end. This model set provides representative inter-patient variability Second, individualised filtered PID and Youla controllers are synthesised for each model in the set. For fairness of comparison, the same performance objective is optimised for all designs, and the same robustness constraints are considered. Controller synthesis is performed utilising convex optimisation and gradient-based methods relying on algebraic differentiation. The worst-case performance over the patient model set is used for the comparison.Results: Two robust filtered PID controllers for the entire model set, as well as individual-specific PID and Youla controllers, were optimised. All considered designs resulted in similar frequency response characteristics. The performance improvement associated with the Youla controllers was not significant compared to the individually tuned filtered PID controllers. The difference in performance between controllers synthesized for the model set and for individual models was significantly larger than the performance difference between the individual-specific PID and Youla controllers. The different controllers were evaluated in simulation. Although all of them showed clinically acceptable results, the robust solutions provided slower responses.Conclusion: Taking the same clinical and technical considerations into account for the optimisation of the different controllers, the design of individual-specific solutions resulted in only marginal differences in performance when comparing an optimal Youla parameter and its optimal filtered PID counterpart. The inter-patient variability is much more detrimental to performance than the limitations imposed by the simple structure of the filtered PID controller.
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| 19. |
- Cederqvist, L, et al.
(författare)
-
Improved Temperature and Depth Control During FSW of Copper Canisters Using Feedforward Compensation
- 2016
-
Ingår i: Friction Stir Welding and Processing VIII. - Hoboken, NJ, USA : John Wiley & Sons, Inc.. - 9781119082491 ; , s. 69-76
-
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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| 20. |
- Cervin, Anton, et al.
(författare)
-
A Matlab Toolbox for Real-Time and Control Systems Co-Design
- 1999
-
Konferensbidrag (refereegranskat)abstract
- The paper presents a Matlab toolbox for simulation of real-time control systems. The basic idea is to simulate a real-time kernel in parallel with continuous plant dynamics. The toolbox allows the user to explore the timely behavior of control algorithms, and to study the interaction between the control tasks and the scheduler. From a research perspective, it also becomes possible to experiment with more flexible approaches to real-time control systems, such as feedback scheduling. The importance of a more unified approach for the design of real-time control systems is discussed. The implementation is described in some detail and a number of examples are given.
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| 21. |
- Cervin, Anton, et al.
(författare)
-
Analysis of Overrun Strategies in Periodic Control Tasks
- 2005
-
Ingår i: Proceedings of the 16th IFAC World Congress. - 008045108X
-
Konferensbidrag (refereegranskat)abstract
- The paper considers period overruns in control tasks with variationsin execution time (or response time). A simple model is used, wherethe input and output operations are assumed to be time-triggered,and the execution-time distribution of the task is assumed to beknown. Three overrun strategies, called Abort, Skip, andQueue, are modeled as discrete-time jump linear systems and areanalyzed with regard to control performance. The analysis isexemplified on an integrator process. It is argued that the Skipstrategy has good performance, is easy to analyze, and is simple toimplement in real-time operating systems. Some extensions to moredynamic models are also given.
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| 22. |
- Cervin, Anton, et al.
(författare)
-
Control loop timing analysis using TrueTime and Jitterbug
- 2006
-
Ingår i: 2006 IEEE Conference on Computer Aided Control System Design, 2006 IEEE International Conference on Control Applications, 2006 IEEE International Symposium on Intelligent Control. - 0780397975 ; , s. 290-295
-
Konferensbidrag (refereegranskat)abstract
- A modern control system is typically implemented as a multitasking software application executing in a real-time operating system. If the computer load is high, the controller will experience delays and jitter, which in turn degrade the control performance. Arguing for an integrated design approach, the paper describes two computer tools for implementation-aware control analysis: TrueTime and Jitterbug. An example is given where the tools are used together to evaluate the performance of various control task implementations
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| 23. |
- Cervin, Anton, et al.
(författare)
-
Control-Scheduling Codesign of Real-Time Systems: The Control Server Approach
- 2005
-
Ingår i: Journal of Embedded Computing. - 1740-4460. ; 1:2, s. 209-224
-
Tidskriftsartikel (refereegranskat)abstract
- The paper presents the control server, a real-time schedulingmechanism tailored to control and signal processing applications. Acontrol server creates the abstraction of a control task with aspecified period and a fixed input-output latency shorter than theperiod. Individual tasks can be combined into more complexcomponents without loss of their individual guaranteed fixed-latencyproperties. I/O occurs at fixed predefined points in time, at whichinputs are read or controller outputs become visible. The controlserver model is especially suited for codesign of real-time controlsystems. The single parameter linking the scheduling design and thecontroller design is the task utilization factor. The proposedserver is an extension of the constant bandwidth server, which isbased on the earliest-deadline-first scheduling algorithm. Theserver has been implemented in a real-time kernel and has also beenvalidated in control experiments on a ball and beam process.
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| 24. |
- Cervin, Anton
(författare)
-
Event-Based Control and Estimation of Server Systems
- 2018
-
Ingår i: Proceedings of the 4th International Conference on Event-Based Control, Communication, and Signal Processing, EBCCSP 2018.
-
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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| 25. |
- Cervin, Anton, et al.
(författare)
-
Feedback-Feedforward Scheduling of Control Tasks
- 2002
-
Ingår i: Real-Time Systems. - 1573-1383. ; 23:1-2, s. 25-53
-
Tidskriftsartikel (refereegranskat)abstract
- A scheduling architecture for real-time control tasks is proposed. The scheduler uses feedback from execution-time measurements and feedforward from workload changes to adjust the sampling periods of the control tasks so that the combined performance of the controllers is optimized. The performance of each controller is described by a cost function. Based on the solution to the optimal resource allocation problem, explicit solutions are derived for linear and quadratic approximations of the cost functions. It is shown that a linear rescaling of the nominal sampling frequencies is optimal for both of these approximations. An extensive inverted pendulum example is presented, where the performance obtained with open-loop, feedback, combined feedback and feedforward scheduling, and earliest-deadline first scheduling are compared. The performance under earliest-deadline first scheduling is explained by studying the behavior of periodic tasks under overload conditions. It is shown that the average values of the sampling periods equal the nominal periods, rescaled by the processor utilization.
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| 26. |
- Cervin, Anton, et al.
(författare)
-
Feedback Scheduling of Control Tasks
- 2000
-
Ingår i: Proceedings of the 39th IEEE Conference on Decision and Control, 2000.. - 0780366387 ; 5, s. 4871-4876
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The paper presents a feedback scheduling mechanism in the context of co-design of the scheduler and the control tasks. We are particularly interested in controllers where the execution time may change abruptly between different modes, such as in hybrid controllers. The proposed solution attempts to keep the CPU utilization at a high level, avoid overload, and distribute the computing resources evenly among the tasks. The feedback scheduler is implemented as a periodic or sporadic task that assigns sampling periods to the controllers based on execution-time measurements. The controllers may also communicate feedforward mode-change information to the scheduler. As an example, we consider hybrid control of a set of double-tank processes. The system is evaluated, from both scheduling and control performance perspectives, by co-simulation of controllers, scheduler, and tanks.
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| 27. |
- Cervin, Anton, et al.
(författare)
-
How Does Control Timing Affect Performance?
- 2003
-
Ingår i: Control Systems Magazine. - 0272-1708. ; 23:3, s. 16-30
-
Tidskriftsartikel (refereegranskat)abstract
- The article presents two Matlab-based tools for analysis andsimulation of real-time control systems: Jitterbug andTrueTime.Jitterbug allows the user to compute aquadratic performance criterion for a linear control system undervarious timing conditions. The control system is described using anumber of continuous- and discrete-time linear systems. Astochastic timing model with random delays is used to describe theexecution of the system. The tool can also be used to investigateaperiodic controllers, multirate controllers, and jitter-compensatingcontrollers.TrueTime facilitates event-based co-simulation of amultitasking real-time kernel containing controller tasks and thecontinuous dynamics of controlled plants. The simulations capture thetrue, timely behavior of real-time controller tasks and communicationnetworks, and dynamic control and scheduling strategies can beevaluated from a control performance perspective. The controllers canbe implemented as Matlab functions, C functions, or ordinarydiscrete-time Simulink blocks.A number of examples that illustrate the use of the tools are given.
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| 28. |
- Cervin, Anton
(författare)
-
Improved Scheduling of Control Tasks
- 1999
-
Konferensbidrag (refereegranskat)abstract
- The paper considers the implementation of digital controllers as real-time tasks in priority-preemptive systems. The performance of a digital feedback control system depends critically on the timing of its sampling and control actions. It is desirable to minimize the computational delay in the controller, as well as the sampling jitter and the control jitter. It is shown that by scheduling the two main parts of a control algorithm as separate tasks, the computational delay can often be reduced significantly. A heuristic method for assigning deadlines to the parts is presented. Further modifications are given to reduce the jitter and to facilitate delay compensation. The result is improved control performance under maintained schedulability.
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| 29. |
- Cervin, Anton
(författare)
-
Integrated Control and Real-Time Scheduling
- 2003
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The topic of the thesis is codesign of flexible real-time control systems. Integrating control theory and real-time scheduling theory, it is possible to achieve higher resource utilization and better control performance. The integration requires new tools for analysis, design, and implementation. The problem of scheduling the individual parts of a control algorithm is studied. It is shown how subtask scheduling can reduce the input-output latency in a set of control tasks. Deadline assignment under different scheduling policies is considered. A feedback scheduling architecture for control tasks is introduced. The scheduler uses feedback from execution-time measurements and feedforward from workload changes to adjust the sampling periods of a set of control tasks so that the combined performance of the controllers is optimized. The Control Server, a novel computational model for real-time control tasks, is presented. The model combines time-triggered I/O with dynamic, reservation-based task scheduling. The model provides short input-output latencies and minimal jitter for the controllers. It also allows control tasks to be treated as scalable real-time components with predictable performance. Two MATLAB-based toolboxes for analysis and simulation of real-time control systems have been developed. The Jitterbug toolbox evaluates a quadratic cost function for a linear control system with timing variations. The tool makes it possible to investigate the impact of delay, jitter, lost samples, etc., on control performance. The TrueTime toolbox facilitates detailed cosimulation of distributed real-time control systems. The scheduling and execution of control tasks is simulated in parallel with the network communication and the continuous process dynamics.
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| 30. |
- Cervin, Anton, et al.
(författare)
-
Jitterbug and TrueTime: Analysis Tools for Real-Time Control Systems
- 2002
-
Konferensbidrag (refereegranskat)abstract
- The paper presents two recently developed, Matlab-based analysis tools for realtime control systems. The first tool, called Jitterbug, is used to compute a performance criterion for a control loop under various timing conditions. The tool makes it easy to quickly judge how sensitive a controller is to implementation effects such as slow sampling, delays, jitter, etc. The second tool, called TrueTime, allows detailed co-simulation of process dynamics, control task execution, and network communication in a distributed real-time control system. Arbitrary scheduling policies may be used, and the tasks may be written in C code, Matlab code, or implemented as Simulink block diagrams.
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| 31. |
- Cervin, Anton, et al.
(författare)
-
Jitterbug - Reference Manual
- 2003
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The manual describes the use of Jitterbug, a Matlab toolbox for analysis of real-time control performance. The tool facilitates the computation of a quadratic performance index for a linear control system under various timing conditions.
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| 32. |
- Cervin, Anton
(författare)
-
JitterTime 1.0—Reference Manual
- 2019
-
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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| 33. |
- Cervin, Anton
(författare)
-
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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| 34. |
- Cervin, Anton, et al.
(författare)
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LQG-Optimal versus Simple Event-Based PID Controllers
- 2020
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Ingår i: 2020 American Control Conference (ACC). - 9781538682661
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Konferensbidrag (refereegranskat)abstract
- In this paper, we study event-based PID control from an optimal stochastic control perspective. The purpose is to better understand what implementation features are critical for achieving good event-based PID performance. For this end, we formulate an LQG control design problem for a double integrator process with an integral disturbance, where the solution is an ideal PID controller. We then consider the trade-off between LQG cost and average sampling rate and give an interpretation of the optimal sampled-data controller and event-based sampling policy in terms of PID control. Based on insights from the optimal solution, we finally discuss how suboptimal but simple event-based PID controllers can be implemented. The proposed implementation is evaluated in a simulation study and compared to earlier work in event-based PID control. The results highlight the importance of considering both the triggering rule and the transmitted information in order to obtain an event-based PID controller with good performance.
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| 35. |
- Cervin, Anton
(författare)
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Merging Real-Time and Control Theory for Improving the Performance of Embedded Control Systems
- 2004
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This report describes the work carried out within the research project ``Merging Real-Time and Control Theory for Improving the Performance of Embedded Control Systems''. The overall objective of the work has been to develop integrated control and scheduling methods for improving the performance of real-time control systems with limited resources. The work has fallen into three categories. First, overrun methods for control tasks has been investigated. Specifically, a reservation-based scheduling concept called the Control Server has been further developed, and control experiments on a ball-and-place process have been performed. Second, the issue of jitter in real-time control systems has been explored. The concept of Jitter Margin has been introduced as a link between control stability theory and scheduling theory. In this context, best-case response-time analysis under earliest-deadline-first scheduling has been researched. Third, some development work on the S.Ha.R.K. real-time kernel has been performed. The rate-monotonic and earliest-deadline-first scheduling modules have been extended, and new modules for the elastic task model and the control server model have been implemented.
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| 36. |
- Cervin, Anton, et al.
(författare)
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On Limit Cycles in Event-Based Control Systems
- 2007
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Ingår i: 46th IEEE Conference on Decision and Control, 2007. ; , s. 1947-1952
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Konferensbidrag (refereegranskat)abstract
- Event-based control is a promising alternative to time-triggered control, especially for systems with limited computation and communication capacities. In the paper, the architecture of a general structure for event-based control is presented. The resulting system has many interesting properties. For instance, a constant load disturbance will typically make the process output oscillate according to a stable limit cycle. Necessary conditions for the limit cycle are given and its local stability is analyzed. Finally, a simple way to achieve integral action based on times between events is proposed.
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| 37. |
- Cervin, Anton, et al.
(författare)
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Optimal On-line Sampling Period Assignment: Theory and Experiments
- 2011
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Ingår i: IEEE Transactions on Control Systems Technology. - 1558-0865. ; 19:4, s. 902-910
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Tidskriftsartikel (refereegranskat)abstract
- In embedded systems, the computing resources are often scarce and several control tasks may have to share the same computer. In this brief, we assume that a set of feedback controllers should be implemented on a single-CPU platform. We study the problem of optimal sampling period assignment, where the goal is to assign sampling rates to the controllers so that the overall control performance is maximized. We derive expressions relating the expected cost over a finite horizon to the sampling period, the computational delay, and the amount of noise acting on the plant. Based on this, we develop a feedback scheduler that periodically assigns new sampling periods based on estimates of the current plant states and noise intensities. Extensive experiments show that online sampling period assignment can deliver significantly better control performance than the state-of-the-art, static period assignment.
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| 38. |
- Cervin, Anton, et al.
(författare)
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Optimal on-line scheduling of multiple control tasks: A case study
- 2006
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Ingår i: Proceedings - Euromicro Conference on Real-Time Systems. - 1068-3070. ; 2006, s. 141-150
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Konferensbidrag (refereegranskat)abstract
- We study the problem of dynamically scheduling a set of state-feedback control tasks controlling a set of linear plants. We consider an on-line non-preemptive scheduling policy that is optimal in the sense that it minimizes a quadratic performance criterion for the overall system. The optimal scheduling decision at each point in time is a function of the states of the controlled plants. To be able to solve the scheduling problem for realistic examples, we use the technique of relaxed dynamic programming to compute suboptimal solutions with error bounds. The approach is compared to earlier approaches in a case study involving simultaneous control of one ball-and-beam process and two DC-servo processes. We also show how the scheduling policy can be modified to allow for background tasks to execute when the need for control is small.
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| 39. |
- Cervin, Anton, et al.
(författare)
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Scheduling of Event-Triggered Controllers on a Shared Network
- 2008
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Konferensbidrag (refereegranskat)abstract
- We consider a system where a number of independent, time-triggered or event-triggered control loops are closed over a shared communication network. Each plant is described by a first-order linear stochastic system. In the event-triggered case, a sensor at each plant frequently samples the output but attempts to communicate only when the magnitude of the output is above a threshold. Once access to the network has been gained, the network is busy for T seconds (corresponding to the communication delay from sensor to actuator), after which the control action is applied to the plant. Using numerical methods, we compute the minimum-variance control performance under various common MAC-protocols, including TDMA, FDMA, and CSMA (with random, dynamic-priority, or static-priority access). The results show that event-triggered control under CSMA gives the best performance throughout.
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| 40. |
- Cervin, Anton, et al.
(författare)
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Simulation of Networked Control Systems Using TrueTime
- 2007
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Konferensbidrag (refereegranskat)abstract
- This paper gives a brief introduction to the TrueTime simulator and then gives several examples on how TrueTime can be used to simulate networked control systems. Among the examples are time-triggered and event-based networked control and AODV routing in wireless ad-hoc networks.
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| 41. |
- Cervin, Anton, et al.
(författare)
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Sporadic Control of Scalar Systems with Delay, Jitter and Measurement Noise
- 2008
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Konferensbidrag (refereegranskat)abstract
- Event-triggered control is a promising alternative to time-triggered control, especially for severely resource-constrained networked embedded systems. Previous work has shown that event-triggered control can reduce both the output variance and the average control rate in scalar linear stochastic systems compared to time-triggered control. It has also been shown how a minimum inter-control interval can be imposed, hence the term ``sporadic control''. In this work we extend the analysis of event-triggered impulse control of first-order linear stochastic systems to handle general sampling intervals and minimum inter-control intervals, control delay and control jitter, and measurement noise. The results show that the advantage of sporadic control remains also in these cases.
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| 42. |
- Cervin, Anton
(författare)
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Stability and Worst-Case Performance Analysis of Sampled-Data Control Systems with Input and Output Jitter
- 2012
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Ingår i: 2012 American Control Conference (ACC). - 9781457710957 ; , s. 3760-3765
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Konferensbidrag (refereegranskat)abstract
- When a feedback controller is implemented in a networked embedded system, the computations and communications induce delays and jitter, which may destabilize the control loop. The majority of previous work on analysis of control loops with time-varying delays has focused on output (actuation) jitter. In many embedded systems, input (sampling) jitter is also an issue. In this paper, we analyze the combined effect of input and output jitter on the stability and performance of linear sampled-data control systems. The analysis is performed via a loop transformation involving two time-varying uncertainties. We show how the input-output gains of the linear part of the transformed system can be computed using a fast-sampling/fast-hold approximation. At the same time, we reduce the conservativeness of a previous stability theorem for pure output jitter.
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| 43. |
- Cervin, Anton, et al.
(författare)
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The Control Server: A Computational Model for Real-Time Control Tasks
- 2003
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Ingår i: Proceedings 15th Euromicro Conference on Real-Time Systems, 2003.. - 0769519369 ; , s. 113-120
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Konferensbidrag (refereegranskat)abstract
- The paper presents a computational model for real-time controltasks, with the primary goal of simplifying the control andscheduling co-design problem. The model combines time-triggered I/Oand inter-task communication with dynamic, reservation-based taskscheduling. To facilitate short input-output latencies, a task maybe divided into several segments. Jitter is reduced by allowingcommunication only at the beginning and at the end of a segment. Akey property of the model is that both schedulability and controlperformance of a control task will depend on the reservedutilization factor only. This enables controllers to be treated asscalable real-time components. The model has been implemented in areal-time kernel and validated in a real-time control application.
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| 44. |
- Cervin, Anton, et al.
(författare)
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The Control Server Model for Co-Design of Real-Time Control Systems
- 2006
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Ingår i: ARTES -- A network for Real-Time research and graduate Education in Sweden 1997--2006.
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Bokkapitel (refereegranskat)abstract
- The paper presents the control server, a real-time scheduling mechanism tailored to control and signal processing applications. A control server creates the abstraction of a control task with a specified period and a fixed input-output latency shorter than the period. Individual tasks can be combined into more complex components without loss of their individual guaranteed fixed-latency properties. I/O occurs at fixed predefined points in time, at which inputs are read or controller outputs become visible. The control server model is especially suited for codesign of real-time control systems. The single parameter linking the scheduling design and the controller design is the task utilization factor. The proposed server is an extension of the constant bandwidth server, which is based on the earliest-deadline-first scheduling algorithm. The server has been implemented in a real-time kernel and has also been validated in control experiments on a ball and beam process.
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| 45. |
- Cervin, Anton, et al.
(författare)
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The Jitter Margin and Its Application in the Design of Real-Time Control Systems
- 2004
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Ingår i: Proceedings of the 10th International Conference on Real-Time and Embedded Computing Systems and Applications.
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Konferensbidrag (refereegranskat)abstract
- Based on recent advances in control theory, we propose the notion of jitter margin for periodic control tasks. The jitter margin isdefined as a function of the amount of constant delay in the controlloop, and it describes how much additional time-varying delay can betolerated before the loop goes unstable. Combined with schedulingtheory, the jitter margin can be used to guarantee the stability andperformance of the controller in the target system. It can also beused as a tool for assigning meaningful deadlines to control tasks.We discuss the need for best-case response-time analysis in thiscontext, and propose a simple lower bound under EDF scheduling.Finally, a control-scheduling codesign procedure is given, whereperiods are assigned iteratively to yield the same relativeperformance degradation for each control task.
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| 46. |
- Cervin, Anton
(författare)
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The Real-Time Control Systems Simulator -Reference manual
- 2000
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- A Matlab / Simulink-based simulator for real-time control systems is described. The simulator facilitates co-simulation of plant dynamics, controller code execution, and real-time scheduling. Three examples are given. The kernel primitives are described in detail.
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| 47. |
- Cervin, Anton
(författare)
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Towards the Integration of Control and Real-Time Scheduling Design
- 2000
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The thesis deals with scheduler and controller co-design for real-time control systems. The overall goal is higher resource utilization and better control performance. One goal is to minimize the performance loss due to jitter and control delays. Another goal is to relax the nominal requirements on hard deadlines and fixed worst-case execution times. A third goal is to provide a co-simulation environment for real-time control systems.
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| 48. |
- 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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| 49. |
- Cervin, Anton
(författare)
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Using Jitterbug to Derive Control Loop Timing Requirements
- 2003
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Ingår i: Proceedings of CERTS'03 – Co-Design of Embedded Real-Time Systems Workshop.
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Konferensbidrag (refereegranskat)abstract
- Linking scheduling attributes to control performance specifications is a difficult problem. This paper discusses how the MATLAB toolbox Jitterbug can be used to derive timing requirements for control loops from various control performance specifications. The resulting timing requirements include specifications on sampling periods, latencies, and jitter. An overview of the Jitterbug approach is given, and limitations of the tool are pointed out. A control design example is given, and, finally, topics where more research is needed are outlined.
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| 50. |
- 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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