| 1. |
- Wallén Axehill, Johanna, et al.
(författare)
-
Estimation-based ILC applied to a parallel kinematic robot
- 2014
-
Ingår i: Control Engineering Practice. - : Elsevier BV. - 0967-0661 .- 1873-6939. ; 33, s. 1-9
-
Tidskriftsartikel (refereegranskat)abstract
- Estimation-based iterative learning control (ILC) is applied to a parallel kinematic manipulator known as the Gantry-Tau parallel robot. The system represents a control problem where measurements of the controlled variables are not available. The main idea is to use estimates of the controlled variables in the ILC algorithm, and in the paper this approach is evaluated experimentally on the Gantry-Tau robot. The experimental results show that an ILC algorithm using estimates of the tool position gives a considerable improvement of the control performance. The tool position estimate is obtained by fusing measurements of the actuator angular positions with measurements of the tool path acceleration using a complementary filter. (C) 2014 Elsevier Ltd. All rights reserved.
|
|
| 2. |
- Amani, Payam, et al.
(författare)
-
Application of Control Theory to a Commercial Mobile Service Support System
- 2012
-
Ingår i: International Journal on Advances in Telecommunications. - 1942-2601. ; 5:3&4
-
Tidskriftsartikel (refereegranskat)abstract
- The Mobile Service Support system (MSS), which Ericsson AB develops, handles the setup of new subscribers and services into a mobile network. Experience from deployed systems show that traffic monitoring and control of the system will be crucial for handling overload situations that may occur at sudden traffic surges. In this paper we identify and explore some important control challenges for this type of systems. Further, we present analysis and experiments showing some advantages of proposed solutions. First, we develop a load-dependent server model for the system, which is validated in testbed experiments. Further, we propose a control design based on the model, and a method for estimation of response times and arrival rates. The main contribution of this paper is that we show how control theory methods and analysis can be used for commercial telecom systems. Parts of our results have been implemented in commercial products, validating the strength of our work.
|
|
| 3. |
- Amani, Payam, et al.
(författare)
-
Multi-step ahead response time prediction for single server queuing systems
- 2011
-
Ingår i: [Host publication title missing].
-
Konferensbidrag (refereegranskat)abstract
- Multi-step ahead response time prediction of CPU constrained computing systems is vital for admission control, overload protection and optimization of resource allocation in these systems. CPU constrained computing systems such as web servers can be modeled as single server queuing systems. These systems are stochastic and nonlinear. Thus, a well-designed nonlinear prediction scheme would be able to represent the dynamics of such a system much better than a linear scheme. A nonlinear autoregressive neural network with exogenous inputs based multi-step ahead response time predictor has been developed. The proposed estimator has many promising characteristics that make it a viable candidate for being implemented in admission control products for computing systems. It has a simple structure, is nonlinear, supports multi-step ahead prediction, and works very well under time variant and non-stationary scenarios such as single server queuing systems under time varying mean arrival rate. Performance of the proposed predictor is evaluated through simulation. Simulations show that the proposed predictor is able to predict the response times of single server queuing systems in multi-step ahead with very good precision represented by very small mean absolute and mean squared prediction errors.
|
|
| 4. |
- Amani, Payam, et al.
(författare)
-
NARX-based multi-step ahead response time prediction for database servers
- 2011
-
Ingår i: [Host publication title missing]. - 2164-7143. - 9781457716768 ; , s. 813-818
-
Konferensbidrag (refereegranskat)abstract
- Advanced telecommunication applications are often based on a multi-tier architecture, with application servers and database servers. With a rapidly increasing development of cloud computing and data centers, characterizations of the dynamics for database servers during changing workloads will be a key factor for analysis and performance improvements in these applications. We propose a multi-step ahead response time predictor for database queries based on a nonlinear autoregressive neural network model with exogenous inputs. The estimator shows many promising characteristics which make it a viable candidate for being implemented in admission control products for database servers. Performance of the proposed predictor is evaluated through experiments on a lab setup with a MySQL-server.
|
|
| 5. |
- Dellkrantz, Manfred, et al.
(författare)
-
Event-Based Response Time Estimation
- 2012
-
Ingår i: [Host publication title missing].
-
Konferensbidrag (refereegranskat)abstract
- Response time is a measure of quality of service in com- puter systems. Estimation techniques, suitable for support systems for mobile phone systems, are explored. These sys- tems are complex queueing systems with large databases. The trac generated by users and system adminstrators changes rapidly, some loads can be measured other cannot. Attempts to capture all details give models that are not suit- able for on-line control. Estimators based on continuous flow models with event based measurements are designed using extended Kalman ltering. The estimators are compared with simple-data based estimators.
|
|
| 6. |
- Dellkrantz, Manfred, et al.
(författare)
-
Performance Modeling and Analysis of a Database Server with Write-Heavy Workload
- 2012
-
Ingår i: [Host publication title missing].
-
Konferensbidrag (refereegranskat)abstract
- Resource-optimization of the infrastructure for service oriented applications require accurate performance models. In this paper we investigate the performance dynamics of a MySQL/InnoDB database server with write-heavy workload. The main objective of our investigation was to understand the system dynamics due to the buffering of disk operations that occurs in database servers with write-heavy workload. In the paper, we characterize the traffic and its periodic anomalies caused by flushing of the buffer. Further, we present a performance model for the response time of the requests and show how this model can be configured to fit with actual database measurements. Also, we show that window-based admission control outperforms rate-based admission control for these types of systems.
|
|
| 7. |
- Freidovich, Leonid B., 1973-, et al.
(författare)
-
Shaping stable periodic motions of inertia wheel pendulum : theory and experiment
- 2009
-
Ingår i: Asian Journal of Control. - : Wiley. - 1561-8625 .- 1934-6093. ; 11:5, s. 549-556
-
Tidskriftsartikel (refereegranskat)abstract
- We consider an underactuated two-link robot called the inertia wheel pendulum. The system consists of a free planar rotational pendulum and a symmetric disk attached to its end, which is directly controlled by a DC-motor. The goal is to create stable oscillations of the pendulum, which is not directly actuated. We exploit a recently proposed feedback-control design strategy based on motion planning via virtual holonomic constraints. This strategy is shown to be useful for design of regulators for achieving orbitally exponentially stable oscillatory motions. The main contribution is a step-by-step procedure on how to achieve oscillations with pre-specified amplitude from a given range and an arbitrary independently chosen period. The theoretical results are verified via experiments with a real hardware setup.
|
|
| 8. |
- Freidovich, Leonid, et al.
(författare)
-
LuGre-Model-Based Friction Compensation
- 2010
-
Ingår i: IEEE Transactions on Control Systems Technology. - 1558-0865 .- 1063-6536. ; 18:1, s. 194-200
-
Tidskriftsartikel (refereegranskat)abstract
- A tracking problem for a mechanical system is considered. We start with a feedback controller that is designed without attention to disturbances, which are assumed to be adequately described by a dynamic LuGre friction model. We are interested in deriving a superimposed observer-based compensator to annihilate or reduce the influence of such a disturbance. We exploit a recently suggested approach for observer design for LuGre-friction-model-based compensation. In order to apply this technique, it is necessary to know the Lyapunov function for the unperturbed system, as well as the parameters of the dynamic friction model, and to verify that a certain structural property satisfied. The case when the system is passive with respect to the matching disturbance related to the given Lyapunov function is illustrated in this brief with a DC-motor example. The main contribution is some new insights into the numerical real-time implementation of a compensator for disturbances describable by one of various LuGre-type models. The other contribution, which is built upon the main one, is experimental verification of the suggested model-based observer design procedure.
|
|
| 9. |
- Johansson, Rolf, et al.
(författare)
-
Observer-based strictly positive real (SPR) variable structure output feedback control
- 2016
-
Ingår i: Journal of the Franklin Institute. - : Elsevier. - 0016-0032 .- 1879-2693. ; 353:16, s. 4213-4232
-
Tidskriftsartikel (refereegranskat)abstract
- This paper considers switching output feedback control of linear systems and variable-structure systems. Theory for stability analysis and design for a class of observer-based feedback control systems is presented. A circle-criterion approach can be used to design an observer-based state feedback control which yields a closed-loop system with specified robustness characteristics. The approach is relevant for variable structure system design with preservation of stability when switching feedback control or sliding mode control is introduced in the feedback loop. It is shown that there exists a Lyapunov function valid over the total operating range and this Lyapunov function has also interpretation as a storage function of passivity-based control. The Lyapunov function can be found by solving a Lyapunov equation, which also generates variable structure switching surfaces. Important applications are to be found in variable structure systems with high robustness requirements.
|
|
| 10. |
- Kihl, Maria, et al.
(författare)
-
Control-theoretic Analysis of Admission Control Mechanisms for Web Server Systems
- 2008
-
Ingår i: World Wide Web. - : Springer Science and Business Media LLC. - 1386-145X .- 1573-1413. ; 11:1, s. 93-116
-
Tidskriftsartikel (refereegranskat)abstract
- Web sites are exposed to high rates of incoming requests. The servers may become overloaded during temporary traffic peaks when more requests arrive than the server is designed for. An admission control mechanism rejects some requests whenever the arriving traffic is too high and thereby maintains an acceptable load in the system. This paper presents how admission control mechanisms can be designed with a combination of queueing theory and control theory. In this paper we model an Apache web server as a GI/G/1-system and then design a PI-controller, commonly used in automatic control, for the server. The controller has been implemented as a module inside the Apache source code. Measurements from the laboratory setup show how robust the implemented controller is, and how it corresponds to the results from the theoretical analysis.
|
|
