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  • 1.
    Abbasi, Jasim Aftab
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Test of Rapid Control System Development using TargetLink2012Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    The aim of this thesis is to employ and evaluate an evaluation board with the standard microprocessor freescale MPC5554EVB board for implementation of control algorithms which are created in Matlab/Simulink instead of using dSPACE prototyping hardware. The Simulink real-time model shall be compiled to the MPC5554EVB board. TargetLink is a powerful software tool which allows an automatic generation of efficient C code from Simulink and facilitates model-based control design. The goal of this thesis is to learn how to use TargetLink in a control design workflow from model to real code and what are the limitations of a microprocessor platform and to evaluate the capabilities of TargetLink to generate a working code for a generic microprocessor.

  • 2. Aguilar, Luis T.
    et al.
    Boiko, Igor M.
    Fridman, Leonid M.
    Freidovich, Leonid B.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Generating oscillations in inertia wheel pendulum via two-relay controller2012Ingår i: International Journal of Robust and Nonlinear Control, ISSN 1049-8923, E-ISSN 1099-1239, Vol. 22, nr 3, s. 318-330Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The problem of generating oscillations of the inertia wheel pendulum is considered. We combine exact feedback linearization with two-relay controller, tuned using frequency-domain tools, such as computing the locus of a perturbed relay system. Explicit expressions for the parameters of the controller in terms of the desired frequency and amplitude are derived. Sufficient conditions for orbital asymptotic stability of the closed-loop system are obtained with the help of the Poincare map. Performance is validated via experiments. The approach can be easily applied for a minimum phase system, provided the behavior of the states of the zero dynamics is of no concern. Copyright (C) 2011 John Wiley & Sons, Ltd.

  • 3.
    Aguilar, Luis T.
    et al.
    CITEDI, National Polytechnic Institute, Tijuana, BC, Mexico.
    Freidovich, Leonid
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Orlov, Yury
    CICESE Research Center, Ensenada, Baja California, Mexico.
    Merida, Jovan
    CITEDI, National Polytechnic Institute, Tijuana, BC, Mexico.
    Performance Analysis of Relay Feedback Position Regulators for Manipulators with Coulomb Friction2013Ingår i: Proc. 12th European Control Conference, NEW YORK, NY 10017 USA: IEEE , 2013, s. 3754-3759Konferensbidrag (Refereegranskat)
    Abstract [en]

    The purpose of the paper is to analyze the performance of several global position regulators for robot manipulators with Coulomb friction. All the controllers include a proportional-differential part and a switched part whereas the difference between the controllers is in the way of compensation of the gravitational forces. Stability analysis is also revisited within the nonsmooth Lyapunov function framework for the controllers with and without gravity pre-compensation. Performance issues of the proposed controllers are evaluated in an experimental study of a five degrees-of-freedom robot manipulator. In the experiments, we choose two criteria for performance analysis. In the first set of experiments, we set the same gains to all the controllers. In the second set of experiments, the gains of the controller were chosen such that the work done by the manipulator is similar.

  • 4. Aguirre-Hernandez, Baltazar
    et al.
    Campos-Canton, Eric
    Villafuerte-Segura, Raul
    Vazquez, Carlos
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Loredo-Villalobos, Carlos-Arturo
    Open Challenges on the Stability of Complex Systems: Insights of Nonlinear Phenomena with or without Delay2019Ingår i: Complexity, ISSN 1076-2787, E-ISSN 1099-0526, artikel-id 5209636Artikel i tidskrift (Övrigt vetenskapligt)
  • 5. Andersson, Alina
    et al.
    Robertsson, Anders
    Shiriaev, Anton S.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik. Norwegian Univ Sci & Technol, Dept Engn Cybernet, Trondheim, Norway.
    Freidovich, Leonid B.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Johansson, Rolf
    Robustness of the Moore-Greitzer Compressor Model's Surge Subsystem with New Dynamic Output Feedback Controllers2014Ingår i: IFAC PAPERSONLINE, Elsevier, 2014, Vol. 47, nr 3, s. 3690-3695Konferensbidrag (Refereegranskat)
    Abstract [en]

    This work presents an extension of a design procedure for dynamic output feedback design for systems with nonlinearities satisfying quadratic constraints. In this work we used an axial gas compressor model described by the 3-state Moore-Greitzer compressor model (MG) that has some challenges for output feedback control design (Planovsky and Nikolaev 1990), (Rubanova 2013). The more general constraints for the investigation of the robustness with respect to parametric uncertainties and measurement noise are shown.

  • 6.
    Appelblad, André
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Development of a Temperature Controlled Cell for Surface Enhanced Raman Spectroscopy for in situ Detection of Gases2014Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Detta dokument beskriver ett examensarbete för civilingenjörsexamen i teknisk fysik vid Umeå Universitet som utförts under vårterminen 2014. I examensarbetet har en kyl-/värmecell för temperaturkontroll av substratytor för ytförstärkt ramanspektroskopi (SERS) för snabb detektion av farliga flyktiga ämnen konstruerats och testats. Arbetet utfördes vid Totalförsvarets forskningsinstitut (FOI) i Umeå, Sverige. Utgångspunkten var ett Linkam Scientific Instruments TS1500 mikroskopsteg, vilket utrustades med ett Peltierelement för kylning/värmning och en termistor för temperaturövervakning. Ett styrsystem baserat på ett Arduino Uno mikrostyrenhetskort konstruerades med ett motordrivkort (H-brygga) vilket använder pulsbreddsmodulering (PWM) för att reglera spänningen till Peltierelementet utifrån en PI-regulator. Den färdiga cellen klarade att reglera temperaturen på ett SERS-substrat i ett temperaturspann på ungefär -15 till +110 °C med en temperaturstabilitet på ±0.22 °C av måltemperaturen. Cellen testades sedan på flyktiga ämnen för att visa dess funktion. Difluorometyl-2,2,2-trifluoro-1-kloroetyleter (isofluran) i gasfas, med instrumentluft som bärargas, flödades genom cellen och SERS-spektra erhölls vid olika koncentrationer och temperaturer. Vid samtliga koncentrationer visades att lägre temperatur ger ökad signalstyrka. När ytan sedan värmdes upp sjönk signalen reversibelt tillbaka till ursprungsvärdet.

    Nyckelord: temperaturkontroll, ytförstärkt ramanspektroskopi, SERS, flyktiga ämnen, Peltierelement, thermistor, PWM, H-brygga, PI(D)-regulator.

  • 7.
    Aranovskiy, Stanislav
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik. The Department of Control Systems and Informatics, National Research University of Information Technologies, Mechanics and Optics, Saint-Petersburg, Russia.
    Freidovich, Leonid
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Adaptive compensation of disturbances formed as sums of sinusoidal signals with application to an active vibration control benchmark2013Ingår i: European Journal of Control, ISSN 0947-3580, E-ISSN 1435-5671, Vol. 19, nr 4, s. 253-265Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    An intuitive solution for the problem of adaptive attenuation of a disturbance formed as a finite sum of unknown sinusoidal signals is proposed for an internally stable discrete-time plant. The compensator is formed as a weighted sum of stable filters. An identification-based procedure for adaptive tuning of the coefficients is proposed for the case of unknown disturbance. We also propose a time-invariant compensator that provides perfect attenuation of a disturbance for the case when a model identification error is sufficiently small and disturbance frequencies are known. The technique is applied to a case study on a challenging benchmark example in the field of active vibration control. Attenuation of a disturbance formed as a sum of up to three sinusoidal signals with unknown/time-varying frequencies is demonstrated via simulation and experimental studies. (C) 2013 European Control Association. Published by Elsevier Ltd. All rights reserved.

  • 8.
    Aranovskiy, Stanislav
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik. Department of Control Systems and Informatics, ITMO University.
    Freidovich, Leonid
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Nikiforova, LV
    Department of Control Systems and Informatics, ITMO University.
    Losenkov, AA
    Department of Control Systems and Informatics, ITMO University.
    МОДЕЛИРОВАНИЕ И ИДЕНТИФИКАЦИЯДИНАМИКИ ЗОЛОТНИКОВОГО ГИДРОРАСПРЕДЕЛИТЕЛЯ: ЧАСТЬ I. МОДЕЛИРОВАНИЕ / ЧАСТЬ II. ИДЕНТИФИКАЦИЯ2013Ingår i: Scientific and Technical Journal «Priborostroenie», ISSN 0021-3454, Vol. 56, nr 4, s. 253-265Artikel i tidskrift (Refereegranskat)
    Abstract [ru]

    ЧАСТЬ I. МОДЕЛИРОВАНИЕ:

    Проанализированы подходы к моделированию гидрораспределителя. Предложена модель динамики золотника в гидрораспределителе, состоящая из двухподсистем — линейной и статически нелинейной.

    ЧАСТЬ II. ИДЕНТИФИКАЦИЯ:

    Предложен метод идентификации параметров модели, использующий датчикидавления и не требующий измерения положения штока золотника. Приведенырезультаты экспериментов.

  • 9.
    Aranovskiy, Stanislav
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik. Department of Control Systems and Informatics, ITMO University, Saint-Petersburg, Russia.
    Losenkov, Andrei
    Department of Control Systems and Informatics, ITMO University, Saint-Petersburg, Russia.
    Vazquez, Carlos
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Position control of an industrial hydraulic system with a pressure compensator2014Ingår i: Proceedings of the 2014 22nd Mediterranean Conference of Control and Automation (MED 2014), Institute of Electrical and Electronics Engineers (IEEE), 2014, s. 1329-1334Konferensbidrag (Refereegranskat)
    Abstract [en]

    A problem of position control of a forestry crane is studied. Several features of industrial hydraulic systems are pointed out, namely a nonlinearity of a valve and a pressure compensator. A novel model of a hydraulic system with the pressure compensator is presented and analyzed, a static nonlinearity inversion and a velocity feedforward control term are introduced. Real-time experiments with controllers which use only position measurements illustrate utility of these terms.

  • 10. Aranovskiy, Stanislav
    et al.
    Vazquez, Carlos
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Control of a single-link mobile hydraulic actuator with a pressure compensator2014Ingår i: 2014 IEEE Conference on Control Applications (CCA), 2014, s. 216-221Konferensbidrag (Refereegranskat)
    Abstract [en]

    A problem of position control of a single-link hydraulic drive, including model uncertainties and disturbances, is studied. Main properties of mobile hydraulic systems are taking into account, namely a nonlinearity of a valve and a pressure compensator. A discontinuous control law coupled with a static nonlinearity inversion and a feed-forward term of velocity is proposed. Besides, a novel model with pressure compensator is presented and the closed-loop stability analysis is provided. Results of experiments carried out on a forestry crane confirm the efficacy of the proposed approach.

  • 11. Bosner, Nela
    et al.
    Karlsson, Lars
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för datavetenskap.
    Parallel and Heterogeneous $m$-Hessenberg-Triangular-Triangular Reduction2017Ingår i: SIAM Journal on Scientific Computing, ISSN 1064-8275, E-ISSN 1095-7197, Vol. 39, nr 1, s. C29-C47Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The m-Hessenberg-triangular-triangular (mHTT) reduction is a simultaneous orthogonal reduction of three matrices to condensed form. It has applications, for example, in solving shifted linear systems arising in various control theory problems. A new heterogeneous CPU/GPU implementation of the mHTT reduction is presented and evaluated against an existing CPU implementation. The algorithm offloads the compute-intensive matrix-matrix multiplications to the GPU and keeps the inner loop, which is memory intensive and has a complicated control flow, on the CPU. Experiments demonstrate that the heterogeneous implementation can be superior to the existing CPU implementation on a system with 2 x 8 CPU cores and one GPU. Future development should focus on improving the scalability of the CPU computations.

  • 12.
    Båmstedt, Ulf
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Umeå marina forskningscentrum (UMF).
    Brugel, Sonia
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    A cost-precision model for marine environmental monitoring, based on time-integrated averages2017Ingår i: Environmental Monitoring & Assessment, ISSN 0167-6369, E-ISSN 1573-2959, Vol. 189, nr 7, artikel-id 354Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Ongoing marine monitoring programs are seldom designed to detect changes in the environment between different years, mainly due to the high number of samples required for a sufficient statistical precision. We here show that pooling over time (time integration) of seasonal measurements provides an efficient method of reducing variability, thereby improving the precision and power in detecting inter-annual differences. Such data from weekly environmental sensor profiles at 21 stations in the northern Bothnian Sea was used in a cost-precision spatio-temporal allocation model. Time-integrated averages for six different variables over 6 months from a rather heterogeneous area showed low variability between stations (coefficient of variation, CV, range of 0.6-12.4%) compared to variability between stations in a single day (CV range 2.4-88.6%), or variability over time for a single station (CV range 0.4-110.7%). Reduced sampling frequency from weekly to approximately monthly sampling did not change the results markedly, whereas lower frequency differed more from results with weekly sampling. With monthly sampling, high precision and power of estimates could therefore be achieved with a low number of stations. With input of cost factors like ship time, labor, and analyses, the model can predict the cost for a given required precision in the time-integrated average of each variable by optimizing sampling allocation. A following power analysis can provide information on minimum sample size to detect differences between years with a required power. Alternatively, the model can predict the precision of annual means for the included variables when the program has a pre-defined budget. Use of time-integrated results from sampling stations with different areal coverage and environmental heterogeneity can thus be an efficient strategy to detect environmental differences between single years, as well as a long-term temporal trend. Use of the presented allocation model will then help to minimize the cost and effort of a monitoring program.

  • 13. Castillo, Ismael
    et al.
    Vazquez, Carlos
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Fridman, Leonid
    Overhead Crane control through LQ Singular Surface Design MATLAB Toolbox2015Ingår i: 2015 AMERICAN CONTROL CONFERENCE (ACC), 2015, s. 5847-5852Konferensbidrag (Refereegranskat)
    Abstract [en]

    The experimental application of LQ Singular Optimal surface design methodology through a MATLAB Toolbox to an overhead crane is presented. Based on the properties of a given performance index, it is possible to apply all the cases of Higher-Order Sliding Mode Controllers, from conventional Sliding Mode Controller up to Higher-Order Sliding Mode Controller of order n, for a specified system. Moreover, it is illustrated how the MATLAB Toolbox can be a helpful tool to select a better performance option. The experimental results confirm the advantages of the proposed control design methodology.

  • 14. Filieri, Antonio
    et al.
    Maggio, Martina
    Angelopoulos, Konstantinos
    D’ippolito, Nicolás
    Gerostathopoulos, Ilias
    Hempel, Andreas Berndt
    Hoffmann, Henry
    Jamshidi, Pooyan
    Kalyvianaki, Evangelia
    Klein, Cristian
    Krikava, Filip
    Misailovic, Sasa
    Papadopoulos, Alessandro Vittorio
    Lund University, Sweden.
    Ray, Suprio
    Sharifloo, Amir M.
    Shevtsov, Stepan
    Ujma, Mateusz
    Vogel, Thomas
    Control Strategies for Self-Adaptive Software Systems2017Ingår i: ACM Transactions on Autonomous and Adaptive Systems, ISSN 1556-4665, E-ISSN 1556-4703, Vol. 11, nr 4, artikel-id 24Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The pervasiveness and growing complexity of software systems are challenging software engineering to design systems that can adapt their behavior to withstand unpredictable, uncertain, and continuously changing execution environments. Control theoretical adaptation mechanisms have received growing interest from the software engineering community in the last few years for their mathematical grounding, allowing formal guarantees on the behavior of the controlled systems. However, most of these mechanisms are tailored to specific applications and can hardly be generalized into broadly applicable software design and development processes.

    This article discusses a reference control design process, from goal identification to the verification and validation of the controlled system. A taxonomy of the main control strategies is introduced, analyzing their applicability to software adaptation for both functional and nonfunctional goals. A brief extract on how to deal with uncertainty complements the discussion. Finally, the article highlights a set of open challenges, both for the software engineering and the control theory research communities.

  • 15.
    Fodor, Szabolcs
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Towards semi-automation of forestry cranes: automated trajectory planning and active vibration damping2017Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Forests represent one of the biggest terrestrial ecosystems of Earth, that can produce important raw renewable materials such as wood with the help of sun, air and water. To efficiently extract these raw materials, the tree harvesting process is highly mechanized in developed countries, meaning that advanced forestry machines are continuously used to fell, to process and to transport the logs and biomass obtained from the forests. However, working with these machines is demanding both mentally and physically, which are known factors to negatively affect operator productivity. Mental fatigue is mostly due to the manual operation of the on-board knuckleboom crane, which requires advanced cognitive work with two joystick levers, while the most serious physical strains arise from cabin vibrations. These vibrations are generated from knuckleboom crane vibrations as a result of aggressive manual operation.

    To enhance operator workload, well-being, and to increase productivity of the logging process, semi-automation functions are suggested, which are supervised automatic executions of specific work elements. Some of the related issues are addressed in the current thesis. Therefore, the content is divided into: (1) the design and development of a semi-automation function focused only on the base joint actuator (slewing actuator) of a knuckleboom crane, and (2) active vibration damping solutions to treat crane structure vibrations induced by the main lift cylinder (inner boom actuator). The considered reference machine is a downsized knuckleboom crane of a forwarder machine, which is used to pick up log assortments from a harvesting site.

    The proposed semi-automation function presented in the first part could be beneficial for operators to use during log loading/unloading scenarios. It consists from a closed-loop position control architecture, to which smooth reference slewing trajectories are provided by a trajectory planner that is automated via operator commands. The used trajectory generation algorithms are taken from conventional robotics and adapted to semi-automation context with proposed modifications that can be customizable by operators.

    Further, the proposed active vibration damping solutions are aimed to reduce vibrations of the knuckleboom crane excited by the inner boom actuator due to aggressive manual commands. First, a popular input shaping control technique combined with a practical switching logic was investigated to deal with the excited payload oscillations. This technique proved to be useful with a fixed crane pose, however it did not provide much robustness in terms of different link configurations. To tackle this problem an H2-optimal controller is developed, which is active in the pressure feedback-loop and its solely purpose is to damp the same payload oscillations. During the design process, operator commands are treated and explained from input disturbance viewpoint.

    All of the hypothesis throughout this thesis were verified with extensive experimental studies using the reference machine.

  • 16.
    Fodor, Szabolcs
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Freidovich, Leonid
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Active vibration damping using H2-optimal feedback control design for forestry cranesManuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    Nowadays, forest harvesting is highly mechanized. The commercially available forestry machines are equipped with knuckleboom cranes that are hydraulically actuated, and manually controlled through a set of joysticks and buttons. A common problem that human operators face during manipulation of such knuckleboom cranes, are the crane structure oscillations created by non-smooth or too aggressive manual joystick-based commands. These oscillations not only contribute to actuator wear, but are also dangerous for operators and the environment as well. The current paper investigates the oscillation attenuation induced by the motion of the inner boom actuator and is based on H2-optimal controller synthesis active in the pressure feedback loop. Furthermore, the controller robustness is verified experimentally considering different working conditions of the reference machine, which also verifies the effectiveness of the approach. 

  • 17.
    Fodor, Szabolcs
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Freidovich, Leonid
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Vázquez, Carlos
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Practical trajectory designs for semi-automation of forestry cranes2016Ingår i: Proceedings of  ISR 2016: 47th International Symposium on Robotics, VDE Verlag GmbH, 2016, s. 1-8Konferensbidrag (Refereegranskat)
    Abstract [en]

    Simplifying the operation of forestry machines with operator-centered semi-automation is needed in the modern timber harvesting industry in order to increase operator productivity and comfort, to reduce learning time of novice operators and to ensure safer manipulation of the cranes. In this paper, useful tools towards operator-centered semi-automation of the base joint actuator of a forwarder crane are proposed. The main goal is to allow comfortable automated motions that do not excite dangerous oscillations of the freely-hanging grapple. Moreover, operator commands are used interactively with a closed-loop position control scheme to assure automated slewing motions. Smooth reference trajectories are provided for the position controller with an on-line trajectory generation algorithm that is developed by combining properties of two standard trajectory generation methods. A practical algorithm based on experiments is introduced to find the trajectory that guaranties minimal grapple oscillations within a set of relatively fast trajectories. Further on, the log loading/unloading tasks are discussed and verified experimentally using the proposed approach on a forwarder crane prototype.

  • 18.
    Fodor, Szabolcs
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Vázquez, Carlos
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Freidovich, Leonid
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Interactive on-line trajectories for semi-automation: case study of a forwarder crane2016Ingår i: Proceedings of 2016 IEEE International Conference on Automation Science and Engineering (CASE), IEEE, 2016, s. 928-933Konferensbidrag (Refereegranskat)
    Abstract [en]

    Working with forestry cranes is not easy due to their complex mechanical structure, non-linear behavior of the hydraulic actuation system, and non-intuitive joint-based control; however, with automation, the level of manipulation difficulty can be reduced. This is potentially useful for the operators since they are prone to be more productive if semi-automation functions are introduced to a certain level. In this paper, a semi-automation function for the base joint actuator of a forestry forwarder crane is proposed. The semi-automation function is based on a design of an interactive on-line trajectory generation algorithm with variable final time that acts as a reference signal to a closed-loop position controller. Moreover, the advantage of this scheme is that the operators are kept in the loop by directly being in charge of controlling the final time for the on-line trajectory generation algorithm. Experiments with a downsized industry-standard forwarder crane verify the applicability and advantage of the proposed scheme.

  • 19.
    Fodor, Szabolcs
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Vázquez, Carlos
    Ålö AB, Umeå, Sweden.
    Freidovich, Leonid
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Sepehri, Nariman
    Towards oscillation reduction in forestry cranes2016Ingår i: Proceedings of the Bath/ASME 2016 Symposium on Fluid Power and Motion Control, ASME Press, 2016, artikel-id V001T01A049Konferensbidrag (Refereegranskat)
    Abstract [en]

    Smooth operation of heavy-duty forestry cranes is not an easy task for the operators with the current joystick-based control method that is complex and non-intuitive. Moreover, abrupt movements of the same joysticks provoke aggressive signals that can lead to oscillatory motions in the actuators and in the entire crane. These oscillations, not only contribute to wear of the joint actuators but also can cause damage to both the operators and the environment; therefore, they must be attenuated. The proposed approach in this paper uses the popular input shaping control technique combined with a practical switching logic to deal with different frequency payload oscillations induced by the motion of the inner boom actuator of a forwarder crane. The results show a significant improvement in terms of visible oscillation reduction monitored through their appearance in the torque signal computed from pressure measurements. Experiments performed on a down-sized forestry crane verifies the effectiveness of the approach.

  • 20.
    Freidovich, Leonid
    Michigan State University.
    Constrained joint PD plus controller for flexible link robots2000Konferensbidrag (Refereegranskat)
    Abstract [en]

    A class of globally asymptotically stable regulators for a finite-dimensional model of robot arm with flexible links under gravity is presented. The control law is formed as the sum of static compensation of gravity at the desired position and constrained state feedback. Only some of generalized coordinates (joint positions and velocities) are assumed available for measurement and saturation in amplifier characteristic curves is taken into account. Copyright (C) 2000 IFAC.

  • 21.
    Freidovich, Leonid
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Control methods for robotic applications: lecture notes2013Bok (Övrigt vetenskapligt)
  • 22.
    Freidovich, Leonid B.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Optimal control for linear systems: lecture notes2013Bok (Övrigt vetenskapligt)
  • 23.
    Freidovich, Leonid
    et al.
    Michigan State University.
    Khalil, Hassan
    Michigan State University.
    Logic-based switching for robust control of minimum-phase nonlinear systems2005Ingår i: Systems & control letters (Print), ISSN 0167-6911, E-ISSN 1872-7956, Vol. 54, nr 8, s. 713-727Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We consider a single-input–single-output minimum-phase nonlinear system with large parametric uncertainty. The system can be represented globally in the normal form and our goal is to find a dynamic output feedback control law to ensure that the output (practically) asymptotically tracks a bounded smooth reference signal. Earlier work used high-gain observers with saturation to derive adaptive as well as robust control laws for this problem. The adaptive control law requires the nonlinear functions to be linearly parameterized in the unknown parameters and could have unsatisfactory transient performance for a large parameter set. The robust control law is based on a worst-case design and could be overly conservative. High gain feedback is needed to implement both controllers in the case when the parameter set is large. As a result, the robust and adaptive controllers may perform poorly in the presence of unmodeled dynamics and measurement noise. In order to reduce the controller gain and improve performance we propose a new approach based on partitioning the set of uncertain parameters into smaller subsets. Robust control laws are designed for each subset and logic based switching is used to choose the appropriate control law. The switching rule uses an estimate of the derivative of a Lyapunov function, which is provided by a high-gain observer.

  • 24.
    Freidovich, Leonid
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Khalil, Hassan
    Michigan State University.
    Logic-based switching for the control of a class of nonlinear systems2003Konferensbidrag (Refereegranskat)
    Abstract [en]

    We consider a nonlinear single-input-single-output minimum phase system with large parametric uncertainty. The system can be represented globally in the normal form and our goal is to find an output dynamic feedback control law to ensure that the output (practically) asymptotically tracks a bounded smooth reference signal. Earlier work used high-gain observers with saturation to derive adaptive as well as robust control laws for this problem. The adaptive control law requires the nonlinear functions to be linearly parameterized in the unknown parameters and could have unsatisfactory transient performance for a large parameter set. The robust control law is based on a worst-case design and could be overly conservative for a large parameter set. In this paper we propose a new approach based on partitioning the set of uncertain parameters into smaller subsets. Robust control laws are designed for each subset and logic based switching is used to choose the appropriate control law. The switching rule uses an estimate of the derivative of a Lyapunov function, which is estimated using a high-gain observer.

  • 25.
    Freidovich, Leonid
    et al.
    Michigan State University.
    Khalil, Hassan K.
    Michigan State University.
    Comparison of logic-based switching control designs for a nonlinear system2004Ingår i: PROCEEDINGS OF THE 2004 AMERICAN CONTROL CONFERENCE, VOLS 1-6, 2004, s. 1221-1222Konferensbidrag (Refereegranskat)
    Abstract [en]

    We consider an example of a second order nonlinear system with large parametric uncertainties. The two parameters of the system are assumed to belong to a finite set. The goal is to guarantee (practical) convergence of the system output to a given constant reference signal. Feedback linearization-based candidate controllers with pole placement are designed for each possible set of parameters. After that, we consider the design of a high-level logic-based supervisor to organize switching between these candidate controllers. Three different approaches are used and compared.

  • 26.
    Freidovich, Leonid
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Khalil, Hassan K.
    Michigan State University.
    Lyapunov-based switching control of nonlinear systems using high-gain observers2005Ingår i: ACC: Proceedings of the 2005 American Control Conference, Vols 1-7, 2005, s. 5103-5108Konferensbidrag (Refereegranskat)
    Abstract [en]

    We consider dynamic output feedback practical stabilization of uniformly observable nonlinear systems, based on high-gain observers with saturation. We assume that uncertain parameters and initial conditions belong to known but comparably large compact sets. In this situation, designs based on traditional robust or adaptive techniques, if applicable, would lead to high controller, observer, and adaptation gains. High gains may excite unmodeled dynamics and significantly amplify measurement noise. Moreover, they could be impossible or too costly to implement. In order to reduce the control efforts and improve robustness of a continuous high-gain-observer-based sliding mode control with respect to these non-ideal operational conditions, we have recently proposed a new logic-based switching design strategy. In this paper, we generalize our technique and apply it to a wider class of nonlinear systems and more general Lyapunov-function-based state and output feedback designs. It is important to notice, in particular, that we require neither the sign of the high-frequency gain to be known nor the system to be minimum-phase. The key idea is to split the set of parameters into smaller subsets, design a controller for each of them, and switch the controller if the derivative of the Lyapunov function does not satisfy a certain inequality, after a dwell-time period. We do not order the candidate controllers in advance, as in our earlier work. Instead, we use estimates of the derivatives of the states, provided by an extended order high-gain observer, to calculate instantaneous performance indices. When the controller is falsified, we switch to a new controller that corresponds to the smallest index among the controllers that have not been falsified yet. This modification is important when the number of candidate controllers is high and pre-routed search may lead to an unacceptable transient performance.

  • 27.
    Freidovich, Leonid
    et al.
    Michigan State University.
    Khalil, Hassan K.
    Michigan State University.
    Universal integral controllers for robotic manipulators2002Ingår i: Nonlinear control systems 2001: (NOLCOS2001) : a proceeding volume from the 5th IFAC Symposium, St. Petersburg, Russia, 4-6 July 2001, Oxford: Pergamon Press, 2002, s. 351-356Konferensbidrag (Refereegranskat)
    Abstract [en]

    As a standard model for a rigid multilink robotic manipulator, we consider a MIMO nonlinear system of uniform vector relative degree {2,...,2}, which has a globally defined normal form with no zero dynamics. We consider a trajectory-following problem for a class of smooth bounded time-varying vector reference signals. We design an output feedback integral controller that ensures ultimately bounded tracking error which could be made as small as required. In addition, if the reference signal has a constant limit, the output approaches this limit. The controller is robust with respect to parameter uncertainties, decentralized, saturated, and simple to implement. Locally, it is a PID regulator with derivatives estimated via a linear high-gain observer. Regional (and semiglobal) practical (and asymptotic) stability is shown with the help of a vector Lyapunov function and a technique, typical for "continuous" sliding mode control. Copyright (C) 2001 IFAC.

  • 28.
    Freidovich, Leonid
    et al.
    Saint Petersburg State Polytechnical University.
    Pervozvanski, Anatoly A.
    St. Petersburg State Polytechnical University.
    Some estimates of performance for PID-like control of robotic manipulators1998Ingår i: ROBOT CONTROL 1997, VOLS 1 AND 2, 1998, s. 85-90Konferensbidrag (Refereegranskat)
    Abstract [en]

    A class of robotic manipulators having prismatic and revolute joints is considered. It is supposed that feedback control laws have proportional-integral-differential (PID) or PID-like forms. It ensures the astatism property of the closed-loop systems. The following results are presented and proved. There are simple inequalities for feedback gains ensuring exponential stability of a desired position under all initial deviations which are small enough. The stability domain can be estimated as well as the stability degree. Under a coordinated growth of coefficients, the stability region is enlarged but the stability degree goes down. The main properties of PID regulated system are not changed if a "dirty" derivatives are used instead of pure ones. PID regulators ensure the tracking with a bounded error under any desired movements which are changed slowly enough.

  • 29.
    Freidovich, Leonid
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Shiriaev, Anton
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Gomez-Estern, Fabio
    Gordillo, Francisco
    Aracil, Javier
    Modification via averaging of partial-energy-shaping control for orbital stabilization: cart-pendulum example2006Ingår i: Proceedings of the 45th IEEE conference on decision and control, vols 1-14, New York: IEEE Press, 2006, s. 6150-6155Konferensbidrag (Refereegranskat)
    Abstract [en]

    We consider the problem of creating oscillations with respect to a part of state variables in underactuated mechanical systems. The main contribution is a modification of a recently proposed control strategy, exploiting passivity to shape the energy of the system with respect to a subset of the state variables and neglecting the dynamics of the other ones. We propose a way to design an additional control action, which guarantees boundedness of the motion of these other degrees of freedom, which otherwise almost always evolve without any bound. The idea is presented on the well-known two-degrees-of-freedom benchmark example of inverted pendulum on a cart.

  • 30.
    Freidovich, Leonid
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Shiriaev, Anton
    Department of Engineering Cybernetics, Norwegian University of Science and Technology.
    Gordillo, F.
    Gomez-Estern, F.
    Aracil, J.
    Partial-energy-shaping control for orbital stabilization of high frequency oscillations of the Furuta pendulum2007Ingår i: PROCEEDINGS OF THE 46TH IEEE CONFERENCE ON DECISION AND CONTROL, VOLS 1-14, 2007, s. 1432-1437Konferensbidrag (Refereegranskat)
    Abstract [en]

    We consider the problem of creating oscillations of the Furuta pendulum around the open-loop unstable equilibrium. Following a recently proposed technique, we start with shaping the energy of the unactuated link. An dissipativity-based controller is designed to create oscillations, neglecting possibility of unbounded motion of the directly actuated link. After that, an auxiliary linear feedback action is added to the control law, stabilizing a desired level of the reshaped energy. Parameters of the controller are tuned to approximately keep the originally created oscillations but ensuring bounded motion of both links. The analysis is valid only for oscillations of sufficiently high frequency and is based on higher order averaging technique. Performance of the designed controller is verified using numerical simulations and experiments.

  • 31. Guerra, Matteo
    et al.
    Vazquez, Carlos
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Efimov, Denis
    Zheng, Gang
    Freidovich, Leonid
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Perruquetti, Wilfrid
    epsilon-Invariant Output Stabilization: Homogeneous Approach and Dead Zone Compensation2015Ingår i: 2015 IEEE 54th Annual Conference on Decision and Control (CDC), 2015, s. 6874-6879Konferensbidrag (Refereegranskat)
    Abstract [en]

    This work addresses the stabilization of dynamical systems in presence of uncertain bounded perturbations using epsilon-invariance theory. Under some assumptions, the problem is reduced to the stabilization of a chain of integrators subject to a perturbation and is treated in two steps. The evaluation of the disturbance and its compensation. Homogeneous observer and control [5], [19] are the tools utilized to achieve a global asymptotic stability and robustness. The result is formally proven and, to validate the theory, it is applied to the control of the telescopic link of a hydraulic actuated industrial crane used in forestry. Experimental results and a comparison with a standard PI controller are presented.

  • 32. Guerra, Matteo
    et al.
    Vazquez, Carlos
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Efimov, Denis
    Zheng, Gang
    Freidovich, Leonid
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Perruquetti, Wilfrid
    Interval Differentiators: on-line estimation of differentiation accuracy2016Ingår i: 2016 EUROPEAN CONTROL CONFERENCE (ECC), IEEE, 2016, s. 1347-1352Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this work an interval observer is proposed for on-line estimation of differentiation errors in some class of high order differentiators (like a high-gain differentiator from [26], or homogeneous nonlinear differentiator from [24 or super twisting differentiator [15]). The results are verified and validated on the telescopic link of a robotic arm for forestry applications in which the mentioned approaches are used to estimate the extension velocity while the interval observer gives bounds to this estimation.

  • 33.
    Hallén, Mattias
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Comminution control using reinforcement learning: Comparing control strategies for size reduction in mineral processing2018Självständigt arbete på avancerad nivå (yrkesexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    In mineral processing the grinding comminution process is an integral part since it is often the bottleneck of the concentrating process, thus small improvements may lead to large savings. By implementing a Reinforcement Learning controller this thesis aims to investigate if it is possible to control the grinding process more efficiently compared to traditional control strategies. Based on a calibrated plant simulation we compare existing control strategies with Proximal Policy Optimization and show possible increase in profitability under certain conditions.

  • 34.
    Hallén, Mattias
    et al.
    ABB Corporate Research.
    Åstrand, Max
    ABB Corporate Research.
    Sikström, Johannes
    Boliden.
    Servin, Martin
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Reinforcement Learning for Grinding Circuit Control in Mineral Processing2019Konferensbidrag (Refereegranskat)
    Abstract [en]

    Grinding, i.e. reducing the particle size of mined ore, is often the bottleneck of the mining concentrating process. Thus, even small improvements may lead to large increases in profit. The goal of the grinding circuit is two-sided; to maximize the throughput of ore, and minimize the resulting particle size of the ground ore within some acceptable range. In this work we study the control of a two-stage grinding circuit using reinforcement learning. To this end, we present a solution for integrating industrial simulation models into the reinforcement learning framework OpenAI Gym. We compare an existing PID controller, based on vast domain knowledge and years of hand-tuning, with a black-box algorithm called Proximal Policy Optimization on a calibrated grinding circuit simulation model. The comparison show that it is possible to control the grinding circuit using reinforcement learning. In addition, contrasting reinforcement learning from the existing PID control, the algorithm is able tomaximize an abstract control goal: maximizing profit as defined by a profit function given by our industrial collaborator. In some operating cases the algorithm is able to control the plant more efficiently compared to existing control.

  • 35.
    Hansson, Anders
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Servin, Martin
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Semi-autonomous shared control of large-scale manipulator arms2010Ingår i: Control Engineering Practice, ISSN 0967-0661, E-ISSN 1873-6939, Vol. 18, nr 9, s. 1069-1076Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Semi-autonomous operation with shared control between the human operator and control computer has been developed and examinedfor a large-scalemanipulator for gripping and lifting heavy objects in unstructured dynamical environments. The technique hasbeen implemented on a electro-hydraulic actuated crane arm with redundant kinematic structure. Several modes of automation andinteraction were evaluated. Experiments show satisfactory smoothness in the transitions between autonomous, shared and manualcontrol, increased performance in log loading for inexperienced operators while experienced operators reported reduced workload.

  • 36. Jonathan Muñoz-Vázquez, Aldo
    et al.
    Vázquez-Aguilera, Carlos
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Parra-Vega, Vicente
    Sánchez-Orta, Anand
    An Exact Robust Differentiator Based on Continuous Fractional Sliding Modes2018Ingår i: Journal of Dynamic Systems Measurement, and Control, ISSN 0022-0434, E-ISSN 1528-9028, Vol. 140, nr 9, artikel-id 091018Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The problem addressed in this paper is the online differentiation of a signal/function that possesses a continuous but not necessarily differentiable derivative. In the realm of (integer) high-order sliding modes, a continuous differentiator provides the exact estimation of the derivative f(over dot)(t), of f(t), by assuming the boundedness of its second-order derivative, f(over double dot)(t), but it has been pointed out that if f(over dot)(t) is casted as a Holder function, then fotthorn is continuous but not necessarily differentiable, and as a consequence, the existence of f(over dot)(t) is not guaranteed, but even in such a case, the derivative of f(t) can be exactly estimated by means of a continuous fractional sliding mode-based differentiator. Then, the properties of fractional sliding modes, as exact differentiators, are studied. The novelty of the proposed differentiator is twofold: (i) it is continuous, and (ii) it provides the finite-time exact estimation of f(over dot)(t), even if fotthorn does not exist. A numerical study is discussed to show the reliability of the proposed scheme.

  • 37.
    Khan, Muhammad Adeel
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Production Code Generation for Rapid Prototyping of Control System using TargetLink2012Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    The objectives of this research is to describe how to generate a production codeautomatically by using TargetLink from Matlab/Simulink for implementing RapidControl Prototyping algorithms on a standard supported microprocessor board and toevaluate the eciency and possible limitations for implementing the generatedproduction code over standard Microprocessor platform MPC5554EVB.

  • 38.
    Klein, Cristian
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för datavetenskap.
    Maggio, Martina
    Lund University.
    Årzén, Karl-Erik
    Lund University.
    Hernández-Rodriguez, Francisco
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för datavetenskap.
    Brownout: Building More Robust Cloud Applications2014Ingår i: 36th International Conference on Software Engineering (ICSE 2014), ACM Digital Library, 2014, s. 700-711Konferensbidrag (Refereegranskat)
    Abstract [en]

    Self-adaptation is a first class concern for cloud applications, which should be able to withstand diverse runtime changes. Variations are simultaneously happening both at the cloud infrastructure level - for example hardware failures - and at the user workload level - flash crowds. However, robustly withstanding extreme variability, requires costly hardware over-provisioning. In this paper, we introduce a self-adaptation programming paradigm called brownout. Using this paradigm, applications can be designed to robustly withstand unpredictable runtime variations, without over-provisioning. The paradigm is based on optional code that can be dynamically deactivated through decisions based on control theory. We modified two popular web application prototypes - RUBiS and RUBBoS - with less than 170 lines of code, to make them brownout-compliant. Experiments show that brownout self-adaptation dramatically improves the ability to withstand flash-crowds and hardware failures.

  • 39.
    Klein, Cristian
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för datavetenskap.
    Maggio, Martina
    Lund University.
    Årzén, Karl-Erik
    Lund University.
    Hernández-Rodriguez, Francisco
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för datavetenskap.
    Introducing Service-level Awareness in the Cloud2013Ingår i: Proceedings of the 4th annual Symposium on Cloud Computing, Association for Computing Machinery (ACM), 2013Konferensbidrag (Refereegranskat)
  • 40.
    Klein, Cristian
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för datavetenskap.
    Maggio, Martina
    Lund University.
    Årzén, Karl-Erik
    Lund University.
    Hernández-Rodriguez, Francisco
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för datavetenskap.
    Introducing Service-level Awareness in the Cloud2013Rapport (Övrigt vetenskapligt)
    Abstract [en]

    Resource allocation in clouds is mostly done assuming hard requirements, applications either receive the requested resources or fail. Given the dynamic nature of workloads, guaranteeing on-demand allocations requires large spare capacity. Hence, one cannot have a system that is both reliable and efficient.

    To solve this issue, we introduce Service-Level (SL) awareness in clouds, assuming applications contain some optional code that can be dynamically deactivated as needed. First, we design a model for such applications and synthesize a controller to decide when to execute the optional code and when to skip it. Then, we propose a Resource Manager (RM) that allocates resources to multiple SL-aware applications in a fair manner. We theoretically prove properties of the overall system using control and game theory.

    To show the practical applicability, we implemented SL-aware versions of RUBiS and RUBBoS with less than 170 lines of code. Experiments show that SL-awareness may enable a factor 8 improvement in withstanding flash-crowds or failures. SL-awareness opens up more flexibility in cloud resource management, which is why we encourage further research by publishing all source code.

  • 41.
    Klein, Cristian
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för datavetenskap.
    Maggio, Martina
    Lund University.
    Årzén, Karl-Erik
    Lund University.
    Hernández-Rodriguez, Francisco
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för datavetenskap.
    Resource management for service level aware cloud applications2013Konferensbidrag (Refereegranskat)
    Abstract [en]

    Resource allocation in clouds is mostly done assuming hard requirements, time-sensitive applications either receive the requested resources or fail. Given the dynamic nature of workloads, guaranteeing on-demand allocations requires large spare capacity. Hence, one cannot have a system that is both reliable and efficient.

    To mitigate this issue, we introduce service-level awareness in clouds, assuming applications contain some optional code that can be dynamically deactivated as needed. We propose a resource manager that allocates resources to multiple service-level-aware applications in a fair manner. To show the practical applicability, we implemented service-level-aware versions of RUBiS and RUBBoS, two popular cloud benchmarks, together with our resource manager. Experiments show that service-level awareness helps in withstanding flash-crowds or failures, opening up more flexibility in cloud resource management.

  • 42.
    Klein, Cristian
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för datavetenskap.
    Papadopoulos, Alessandro Vittorio
    Lund University, Sweden.
    Dellkrantz, Manfred
    Lund University, Sweden.
    Dürango, Jonas
    Lund University, Sweden.
    Maggio, Martina
    Lund University.
    Årzén, Karl-Erik
    Lund University.
    Hernández-Rodriguez, Francisco
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för datavetenskap.
    Elmroth, Erik
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för datavetenskap.
    Improving Cloud Service Resilience using Brownout-Aware Load-Balancing2014Ingår i: 2014 IEEE 33RD INTERNATIONAL SYMPOSIUM ON RELIABLE DISTRIBUTED SYSTEMS (SRDS), IEEE Computer Society, 2014, s. 31-40Konferensbidrag (Refereegranskat)
    Abstract [en]

    We focus on improving resilience of cloud services (e.g., e-commerce website), when correlated or cascading failures lead to computing capacity shortage. We study how to extend the classical cloud service architecture composed of a load-balancer and replicas with a recently proposed self-adaptive paradigm called brownout. Such services are able to reduce their capacity requirements by degrading user experience (e.g., disabling recommendations).

    Combining resilience with the brownout paradigm is to date an open practical problem. The issue is to ensure that replica self-adaptivity would not confuse the load-balancing algorithm, overloading replicas that are already struggling with capacity shortage. For example, load-balancing strategies based on response times are not able to decide which replicas should be selected, since the response times are already controlled by the brownout paradigm.

    In this paper we propose two novel brownout-aware load-balancing algorithms. To test their practical applicability, we extended the popular lighttpd web server and load-balancer, thus obtaining a production-ready implementation. Experimental evaluation shows that the approach enables cloud services to remain responsive despite cascading failures. Moreover, when compared to Shortest Queue First (SQF), believed to be near-optimal in the non-adaptive case, our algorithms improve user experience by 5%, with high statistical significance, while preserving response time predictability.

  • 43.
    La Hera, Pedro
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Underactuated mechanical systems: Contributions to trajectory planning, analysis, and control2011Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Nature and its variety of motion forms have inspired new robot designs with inherentunderactuated dynamics. The fundamental characteristic of these controlled mechanicalsystems, called underactuated, is to have the number of actuators less than the number ofdegrees of freedom. The absence of full actuation brings challenges to planning feasibletrajectories and designing controllers. This is in contrast to classical fully-actuated robots.A particular problem that arises upon study of such systems is that of generating periodicmotions, which can be seen in various natural actions such as walking, running,hopping, dribbling a ball, etc. It is assumed that dynamics can be modeled by a classicalset of second-order nonlinear differential equations with impulse effects describing possibleinstantaneous impacts, such as the collision of the foot with the ground at heel strikein a walking gait. Hence, we arrive at creating periodic solutions in underactuated Euler-Lagrange systems with or without impulse effects. However, in the qualitative theory ofnonlinear dynamical systems, the problem of verifying existence of periodic trajectoriesis a rather nontrivial subject.The aim of this work is to propose systematic procedures to plan such motions and ananalytical technique to design orbitally stabilizing feedback controllers. We analyze andexemplify both cases, when the robotmodel is described just by continuous dynamics, andwhen continuous dynamics is interrupted from time to time by state-dependent updates.For trajectory planning, systems with one or two passive links are considered, forwhich conditions are derived to achieve periodicmotions by encoding synchronizedmovementsof all the degrees of freedom. For controller design we use an explicit form tolinearize dynamics transverse to the motion. This computation is valid for an arbitrarydegree of under-actuation. The linear system obtained, called transverse linearization, isused to analyze local properties in a vicinity of the motion, and also to design feedbackcontrollers. The theoretical background of these methods is presented, and developedin detail for some particular examples. They include the generation of oscillations forinverted pendulums, the analysis of human movements by captured motion data, and asystematic gait synthesis approach for a three-link biped walker with one actuator.

  • 44. La Hera, Pedro
    et al.
    Morales, Daniel Ortiz
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Model-Based Development of Control Systems for Forestry Cranes2015Ingår i: Journal of Control Science and Engineering, ISSN 1687-5249, E-ISSN 1687-5257, Vol. 2015, artikel-id 256951Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Model-based methods are used in industry for prototyping concepts based on mathematical models. With our forest industry partners, we have established a model-based workflow for rapid development of motion control systems for forestry cranes. Applying this working method, we can verify control algorithms, both theoretically and practically. This paper is an example of this workflow and presents four topics related to the application of nonlinear control theory. The first topic presents the system of differential equations describing the motion dynamics. The second topic presents nonlinear control laws formulated according to sliding mode control theory. The third topic presents a procedure for model calibration and control tuning that are a prerequisite to realize experimental tests. The fourth topic presents the results of tests performed on an experimental crane specifically equipped for these tasks. Results of these studies show the advantages and disadvantages of these control algorithms, and they highlight their performance in terms of robustness and smoothness.

  • 45.
    La Hera, Pedro
    et al.
    Sveriges lantbruksuniversitet .
    Ortiz Morales, Daniel
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Designing and testing control systems for forestry cranesManuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    Motivated by the interest, and in collaboration of forestry machine manufacturers, a number of motion control algorithms have been designed, implemented, and tested in a forwarder crane. The aim has been to achieve the robust tracking of reference link motion trajectories based on sensory feedback coming from pressure and angular displacement sensors mounted in the manipulator. To this end, a procedure employing computer aided model-based methods and simulation technology have been suggested, in order to produce systematical tools for model analysis, tuning of controllers, and rapid prototyping for hardware-in-the-loop testing. The controllers derived have the objective to form the background of a new generation of crane control modes, which will be subsequently designed by the use of different motion planning techniques. We present results of experimental studies carried out on a medium-size crane, which has been properly equipped for the task of rapid-prototyping.

  • 46.
    La Hera, Pedro
    et al.
    Sveriges lantbruksuniversitet .
    Ortiz Morales, Daniel
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Non-linear dynamics modelling description for simulating the behavior of forestry cranes2014Ingår i: International journal of Modeling, identification and control, ISSN 1746-6172, E-ISSN 1746-6180, Vol. 21, nr 2, s. 125-138Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Model-based design is a standard framework widely adopted in modern industry. It is used for designing multi-domain engineering solutions based on computer-aided simulation technology. Currently, this approach is also being viewed as a tentative method for designing modern heavy-duty machine technology. Under this motivation, our aim is to present how modeling techniques can be used for simulating dynamics of forestry machines. To this end, we consider a forestry crane, and propose mathematical models and calibration techniques, such that model-based methods can subsequently be applied. The complexity of the machine is represented by first principle laws, in which the mechanical system is modeled by Euler-Lagrange formulations, and the hydraulic system is modeled by principles of fluid dynamics. The calibration algorithms are performed by statistical algorithms based on linear and nonlinear least-squares methods. The results of simulation show a significant correspondence between the simulated and observed variables, validating our procedures.

  • 47.
    Larsson, Per-Anton
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Funktionsbeskrivning konvertergassystem2014Självständigt arbete på grundnivå (högskoleexamen), 5 poäng / 7,5 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Arbetet som presenteras i denna rapport har utförts på R1K, vilket är en avdelning på Rönnskärsverken, som är en del av New Bolidens koncern. 2007 byggdes ett nytt gassystem med ett flertal nya komponenter. Till detta gassystem fanns bristande information om hur dessa komponenter fungerar och hänger ihop. Detta examensjobb har till syfte att skapa en funktionsbeskrivning i form av en lättläst operatörsmanual, för nya och erfarna operatörer. Informationen till funktionsbeskrivningen har kompilerats från tillverkarmanualer, konstruktionsritningar, informationspärmar, intervjuer samt ABB styrsystem. Bilder har tagits och redigerats, för att ge en illustrativ överblick av fluider och gasers väg genom gassystemet och dess kringutrustning. Information och bilder har sedan sammanställts i en funktionsbeskrivning (Se bilaga 1).

  • 48.
    Lind, Emelie
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Modeling and Measurement of Gas Flow for Engines with EGR2013Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
  • 49. Low, Emily MP
    et al.
    Manchester, Ian R
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Savkin, Andrey V
    A biologically inspired method for vision-based docking of wheeled mobile robots2007Ingår i: Robotics and Autonomous Systems, ISSN 0921-8890, E-ISSN 1872-793X, Vol. 55, nr 10, s. 769-784Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present a new control law for the problem of docking a wheeled robot to a target at a certain location with a desired heading. Recent research into insect navigation has inspired a solution which uses only one video camera. The control law is of the "behavioral" type in that all control actions are based on immediate visual information. Docking success under certain conditions is proved mathematically and simulation studies show the control law to be robust to camera intrinsic parameter errors. Experiments were performed for verification of the control law.

  • 50. Lu, Ying
    et al.
    Williams, Jedediyah
    Trinkle, Jeff
    Lacoursiere, Claude
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Högpresterande beräkningscentrum norr (HPC2N).
    A FRAMEWORK FOR PROBLEM STANDARDIZATION AND ALGORITHM COMPARISON IN MULTIBODY SYSTEM2014Ingår i: PROCEEDINGS OF THE ASME INTERNATIONAL DESIGN ENGINEERING TECHNICAL CONFERENCES AND COMPUTERS AND INFORMATION IN ENGINEERING CONFERENCE, 2014, VOL 6, 2014, Vol. 6, artikel-id V006T10A016Konferensbidrag (Refereegranskat)
    Abstract [en]

    The underlying dynamic model of multibody systems takes the form. of a differential Complementarity Problem (dCP), which is nonsmooth and thus challenging to integrate. The dCP is typically solved by discretizing it in time, thus converting the simulation problem into the problem of solving a sequence of complementarity problems (CPs). Because the CPs are difficult to solve, many modelling options that affect the dCPs and CPs have been tested, and some reformulation and relaxation options affecting the properties of the CPs and solvers have been studied in the hopes to find the "best" simulation method. One challenge within the existing literature is that there is no standard set of benchmark simulations. In this paper, we propose a framework of Benchmark Problems for Multibody Dynamics (BPMD) to support the fair testing of various simulation algorithms. We designed and constructed a BPMD database and collected an initial set of solution algorithms for testing. The data stored for each simulation problem is sufficient to construct the CPs corresponding to several different simulation design decisions. Once the CPs are constructed from the data, there are several solver options including the PATH solver, nonsmooth Newton methods, fixed-point iteration methods for nonlinear problems, and Lemke's algorithm for linear problems. Additionally, a user-friendly interface is provided to add customized models and solvers. As an example benchmark comparison, we use data from physical planar grasping experiments. Using the input from a physical experiment to drive the simulation, uncertain model parameters such as friction coefficients are determined. This is repeated for different simulation methods and the parameter estimation error serves as a measure of the suitability of each method to predict the observed physical behavior.

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