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  • 1.
    Abbasi, Jasim Aftab
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Test of Rapid Control System Development using TargetLink2012Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    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 University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Generating oscillations in inertia wheel pendulum via two-relay controller2012In: International Journal of Robust and Nonlinear Control, ISSN 1049-8923, E-ISSN 1099-1239, Vol. 22, no 3, p. 318-330Article in journal (Refereed)
    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 University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    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 Friction2013In: Proc. 12th European Control Conference, NEW YORK, NY 10017 USA: IEEE , 2013, p. 3754-3759Conference paper (Refereed)
    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 University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Loredo-Villalobos, Carlos-Arturo
    Open Challenges on the Stability of Complex Systems: Insights of Nonlinear Phenomena with or without Delay2019In: Complexity, ISSN 1076-2787, E-ISSN 1099-0526, article id 5209636Article in journal (Other academic)
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  • 5.
    Amkoff, Leon
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Trailer Simulation Model for an Indirect Tire Pressure Monitoring System2021Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    A car with underinflated tires can lead to both safety and environmental issues. To combat this, markets have begun requiring new cars to feature a Tire Pressure Monitoring System. Systems without pressure sensors are referred to as indirect Tire Pressure Monitoring Systems, often utilizing wheel speed sensors in combination with other available sensor information to detect tire pressure losses. 

    NIRA Dynamics is a company founded in Linköping, Sweden, most known for its indirect Tire Pressure Monitoring System called TPI. TPI needs to be verified in a large number of scenarios, which may be both difficult and expensive to realize in real vehicle tests. The purpose of this master thesis was to investigate and model what physical phenomena are associated with having a trailer connected to a car, relevant for TPI. The goal was to construct a hybrid simulation framework, making it possible to modify car-only data to reflect the effects of having a trailer connected. 

    A car-trailer model was developed, showing close resemblance in simulations to real collected car-trailer sensor data. The model was then used to design a hybrid simulation framework, where car-only sensor signals were modified to mimic having different types of trailers attached. The hybrid simulation results show close resemblance to real collected trailer sensor data. By not requiring real trailer data for every scenario to evaluate software performance on, the proposed framework opens up the possibility to simulate data from a much larger number of trailer combinations than would otherwise have been feasible to test in real vehicle tests. 

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  • 6. Andersson, Alina
    et al.
    Robertsson, Anders
    Shiriaev, Anton S.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics. Norwegian Univ Sci & Technol, Dept Engn Cybernet, Trondheim, Norway.
    Freidovich, Leonid B.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Johansson, Rolf
    Robustness of the Moore-Greitzer Compressor Model's Surge Subsystem with New Dynamic Output Feedback Controllers2014In: Proceedings of the 19th World Congress, The International Federation of Automatic Control / [ed] Xia X.,Boje E., Elsevier, 2014, Vol. 47, no 3, p. 3690-3695Conference paper (Refereed)
    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.

  • 7.
    Andersson, Jennifer
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics. Umeå universitet.
    Bodin, Kenneth
    Algoryx Simulation AB, Umeå, Sweden.
    Lindmark, Daniel
    Algoryx Simulation AB, Umeå, Sweden.
    Servin, Martin
    Umeå University, Faculty of Science and Technology, Department of Physics. Algoryx Simulation AB, Umeå, Sweden.
    Wallin, Erik
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Reinforcement Learning Control of a Forestry Crane Manipulator2021In: 2021 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS 2021): Proceedings, Prague: IEEE Robotics and Automation Society, 2021, p. 2121-2126Conference paper (Refereed)
    Abstract [en]

    Forestry machines are heavy vehicles performing complex manipulation tasks in unstructured production forest environments. Together with the complex dynamics of the on-board hydraulically actuated cranes, the rough forest terrains have posed a particular challenge in forestry automation. In this study, the feasibility of applying reinforcement learning control to forestry crane manipulators is investigated in a simulated environment. Our results show that it is possible to learn successful actuator-space control policies for energy efficient log grasping by invoking a simple curriculum in a deep reinforcement learning setup. Given the pose of the selected logs, our best control policy reaches a grasping success rate of 97%. Including an energy-optimization goal in the reward function, the energy consumption is significantly reduced compared to control policies learned without incentive for energy optimization, while the increase in cycle time is marginal. The energy-optimization effects can be observed in the overall smoother motion and acceleration profiles during crane manipulation. 

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  • 8.
    Appelblad, André
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Development of a Temperature Controlled Cell for Surface Enhanced Raman Spectroscopy for in situ Detection of Gases2014Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This work describes a master’s thesis in engineering physics at Umeå University carried out during the spring semester of 2014. In the thesis the student has constructed and tested a temperature controlled cell for cooling/heating of surface-enhanced-Raman-spectroscopy (SERS) substrates for rapid detection of volatile substances. The thesis was carried out at the Swedish Defence Research Agency (FOI) in Umeå, Sweden. A Linkam Scientific Instruments TS1500 cell was equipped with a Peltier element for cooling/heating and a thermistor temperature sensor. A control system was constructed, based on an Arduino Uno microcontroller board and a pulse-width-modulated (PWM) H-bridge motor driver to control the Peltier element using a proportional-integral (PI) control algorithm. The temperature controlled cell was able to regulate the temperature of a SERS substrate within -15 to +110 °C and maintain the temperature over prolonged periods at ±0.22 °C of the set point temperature. Gas phase of 2-chloro-2-(difluoromethoxy)-1,1,1-trifluoro-ethane (isoflurane) was flowed through the cell and SERS spectra were collected at different temperatures and concentrations. This test showed that the signal is increased when the substrate is cooled and reversibly decreased when the substrate was heated.

    Keywords: temperature control, Raman scattering, surface enhanced Raman spectroscopy SERS, SERS substrate, volatile substances, Peltier module, thermistor, PWM, H-bridge, PI(D) control.

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  • 9.
    Aranovskiy, Stanislav
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics. The Department of Control Systems and Informatics, National Research University of Information Technologies, Mechanics and Optics, Saint-Petersburg, Russia.
    Freidovich, Leonid
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Adaptive compensation of disturbances formed as sums of sinusoidal signals with application to an active vibration control benchmark2013In: European Journal of Control, ISSN 0947-3580, E-ISSN 1435-5671, Vol. 19, no 4, p. 253-265Article in journal (Refereed)
    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.

  • 10.
    Aranovskiy, Stanislav
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics. Department of Control Systems and Informatics, ITMO University.
    Freidovich, Leonid
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    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. ИДЕНТИФИКАЦИЯ2013In: Scientific and Technical Journal «Priborostroenie», ISSN 0021-3454, Vol. 56, no 4, p. 253-265Article in journal (Refereed)
    Abstract [en]

    MODELING AND IDENTIFICATION OF DYNAMICS OF A HYDRAULIC ACTUATOR WITH A SPOOL VALVE. PART I. MODELING

    Approaches to the problem of modeling of hydraulic actuator are considered. A model for the spool dynamics consisting of a linear block and two static nonlinear subsystems is presented.

    MODELING AND IDENTIFICATION OF DYNAMICS OF A HYDRAULIC ACTUATOR WITH A SPOOL VALVE. PART II: IDENTIFICATION

    A method for identification of dynamic model parameters is suggested for the case when only pressures in the hydraulic cylinders but not the valve displacements are measured. The approach is verified by presented results of experiments.

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  • 11.
    Aranovskiy, Stanislav
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics. 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 University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Position control of an industrial hydraulic system with a pressure compensator2014In: Proceedings of the 2014 22nd Mediterranean Conference of Control and Automation (MED 2014), Institute of Electrical and Electronics Engineers (IEEE), 2014, p. 1329-1334Conference paper (Refereed)
    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.

  • 12. Aranovskiy, Stanislav
    et al.
    Vazquez, Carlos
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Control of a single-link mobile hydraulic actuator with a pressure compensator2014In: 2014 IEEE Conference on Control Applications (CCA), 2014, p. 216-221Conference paper (Refereed)
    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.

  • 13. Bosner, Nela
    et al.
    Karlsson, Lars
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Parallel and Heterogeneous $m$-Hessenberg-Triangular-Triangular Reduction2017In: SIAM Journal on Scientific Computing, ISSN 1064-8275, E-ISSN 1095-7197, Vol. 39, no 1, p. C29-C47Article in journal (Refereed)
    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.

  • 14.
    Båmstedt, Ulf
    et al.
    Umeå University, Faculty of Science and Technology, Umeå Marine Sciences Centre (UMF).
    Brugel, Sonia
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    A cost-precision model for marine environmental monitoring, based on time-integrated averages2017In: Environmental Monitoring & Assessment, ISSN 0167-6369, E-ISSN 1573-2959, Vol. 189, no 7, article id 354Article in journal (Refereed)
    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.

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  • 15.
    Castillo, Ismael
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Freidovich, Leonid B.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Describing-function-based analysis to tune parameters of chattering reducing approximations of Sliding Mode controllers2020In: Control Engineering Practice, ISSN 0967-0661, E-ISSN 1873-6939, Vol. 95, article id 104230Article in journal (Refereed)
    Abstract [en]

    Sliding Mode Control (SMC) is a powerful feedback control design technique leading to insensitivity to certain types of disturbances under ideal conditions. Among these conditions, there are discontinuity in the generated control signal and absence of unmodeled dynamics. In many cases, the former maybe not implementable while the latter is often not holdable. Such non-ideal conditions typically excite high-frequency oscillations, known as chattering, not only in the input to the plant but also in the output, leading to a degradation of performance and losing the attractive insensitivity property. One of well-known and widely used approaches to achieve chattering reduction, caused by delays, parasitic dynamics, unmatched perturbations, etc., is implicitly or explicitly approximating the discontinuity. Theoretically, removing the discontinuities in the input to the plant, as well as in the internal controller dynamics, leads to loosing the insensitivity property under ideal conditions, but may insure better performance under more realistic conditions. This paper presents a Describing Function analysis in frequency domain of some SMC algorithms under presence of unmodeled (parasitic) dynamics, in the case when the discontinuous sign function is replaced or approximated by a saturation function. We are to concentrate here on a systematic procedure to tune parameters of the approximation.

  • 16. Castillo, Ismael
    et al.
    Vazquez, Carlos
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Fridman, Leonid
    Overhead Crane control through LQ Singular Surface Design MATLAB Toolbox2015In: 2015 AMERICAN CONTROL CONFERENCE (ACC), 2015, p. 5847-5852Conference paper (Refereed)
    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.

  • 17.
    Dalberg, Niklas
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    EFFEKTIVISERING AV ENERGIANVÄNDNING FÖR MARKVÄRME MED HJÄLP AV VÄDERPROGNOSER2023Independent thesis Basic level (professional degree), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Ground heating is used to keep walkways and parking lots free from snow and ice. These systems are usually controlled based on real-time data obtained directly from the facility. These ground heating systems consume large amounts of energy, and the purpose of this project was to optimally and individually control the operation based on future weather forecasts in order to minimize energy consumption.

     

    Based on the current ground temperature and future weather forecasts, it is possible to create a model of the future temperature of the ground. Using the future ground temperature, as well as past and future precipitation intensity, it is possible to identify potentially hazardous conditions that will require ground heating. Once this need is identified, the time it will take to heat the ground to a specific temperature and melt all the precipitation on the ground is calculated.

     

    After all the precipitation has melted, the process of drying the ground begins. With a surface runoff factor of 0.9, it is assumed that 90% of all precipitation will run off from the road. Based on the ground temperature and various weather parameters, the evaporation time for the remaining 10% of precipitation still on the ground is calculated. When all the precipitation has evaporated and no new precipitation is expected within three hours, the ground is considered dry, and the system stops operating.

     

    The system was tested using data from February 2023 and compared with the operation of the ground heating system at one of GateIBS facilities. The logic for starting the operation was tested separately from the logic for stopping the operation. The new system would initiate the operation twice in February with a precipitation threshold set at 3mm and 5mm, and three times with the threshold set at 1mm. This is a drastic reduction compared to the actual ground heating system, which started a total of ten times during the same month. The logic for stopping the operation was tested only when the actual ground heating system was in operation, and throughout the month, the new system would have stopped the operation 50 hours earlier, resulting in a total reduction in operating time of 29.2% and a reduction in energy use by 28.5%.

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  • 18. Elias Ortega Paredes, Abraham
    et al.
    Nunes, Lauro Roberto
    Dias Santos, Max Mauro
    de Menezes, Leonardo Rodrigues Araujo Xavier
    Silvia Collazos Linares, Kathya
    Francisco Justo, Joao
    Gu, Zonghua
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Simulation Performance Enhancement in Automotive Embedded Control Using the Unscented Transform2020In: IEEE Access, E-ISSN 2169-3536, Vol. 8, p. 222041-222049Article in journal (Refereed)
    Abstract [en]

    Automotive embedded systems comprise several domains, such as in software, electrical, electronics, and control. When designing and testing functions at the top level, one generally ignores the uncertainties arising from the electrical and electronic effects, which could lead to an irregular behavior and deteriorate their performance even using the appropriate methodology for designing the embedded control systems. Then, the studies and comparison on the effect of uncertainty in the automotive domain are important to improve the overall performance of those control systems. Here, we explored the uncertainty in control systems using the Monte Carlo (MC) and unscented transform (UT) methods. These methods have been applied to a mobile seat platform (MSP) and a light emitting diode (LED) used for lighting of heavy-duty vehicles. The UT for embedded control systems has shown better performance when compared to the Monte Carlo method, in order to reduce the number of required variables and computational resources in the simulation of failures and test-case generation. Finally, this investigation brings another application for the UT, in order to exemplify its applicability and advantages when compared with the other methods.

  • 19.
    Eriksson, Philip
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Sandberg, Erik
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Val och implementering av en varvtalssensor i växellådan på ett elektrifierat bandvagn2021Independent thesis Basic level (professional degree), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    This project was carried out in cooperation with the company BAE Systems Hägglunds AB in Örnsköldsvik, which produces vehicles for military as well as civil use. There is an ongoing project at BAE researching bandwagons using electricity as their source of energy, codename SIRIUS, and this investigation is part of it. The purpose of this thesis is to investigate how to efficiently measure differences in rotational speed of affected gears inside of the gearbox in the vehicle. This is to enable efficient gearshift while the vehicle is in motion.

    Initially, different types of sensors are presented along with how they are used in diverse applications. The most relevant type of sensors is using technology based on electromagnetism. Calculations are then performed to control the accuracy of the sensor along with the ideal number of magnetic nodes based on the data sheet provided by the manufacturer. These parameters are then used to create the optimal amount of measuring nodes on the constructed disc that will beimplemented. Beyond that the difference in rotational speed between the main axis and the shifted gear were calculated to see how large difference in rotational speed the gears can handle during gearshift. The chosen sensor is based on the Hall effect and is called mini-HA-P Sealed made by BOSCH. The demands to be able to measure accurate data within the harsh environment of a gearbox are fulfilled by the sensor.

    A concept for mounting the sensor on the gearbox was developed using CAD focusing on ease of maintenance and other outside factors affecting correct measurement data such as stray magnetic fields, vibrations, and large temperature changes. Drawings of two different components were created to aid in this measuring and minor changes to the gearbox were carried out. The project also creates new aspects of research that require further investigation, for example flow analysis, material analysis and a way to convert the excess energy from retardation when the rotational speed is decreased. 

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  • 20. 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 Systems2017In: ACM Transactions on Autonomous and Adaptive Systems, ISSN 1556-4665, E-ISSN 1556-4703, Vol. 11, no 4, article id 24Article in journal (Refereed)
    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.

  • 21.
    Fodor, Szabolcs
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Towards semi-automation of forestry cranes: automated trajectory planning and active vibration damping2017Doctoral thesis, comprehensive summary (Other academic)
    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.

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  • 22.
    Fodor, Szabolcs
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Freidovich, Leonid
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Active vibration damping using H2-optimal feedback control design for forestry cranesManuscript (preprint) (Other academic)
    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. 

  • 23.
    Fodor, Szabolcs
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Freidovich, Leonid
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Vázquez, Carlos
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Practical trajectory designs for semi-automation of forestry cranes2016In: Proceedings of  ISR 2016: 47th International Symposium on Robotics, VDE Verlag GmbH, 2016, p. 1-8Conference paper (Refereed)
    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.

  • 24.
    Fodor, Szabolcs
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Vázquez, Carlos
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Freidovich, Leonid
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Interactive on-line trajectories for semi-automation: case study of a forwarder crane2016In: Proceedings of 2016 IEEE International Conference on Automation Science and Engineering (CASE), IEEE, 2016, p. 928-933Conference paper (Refereed)
    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.

  • 25.
    Fodor, Szabolcs
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Vázquez, Carlos
    Ålö AB, Umeå, Sweden.
    Freidovich, Leonid
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Sepehri, Nariman
    Towards oscillation reduction in forestry cranes2016In: Proceedings of the Bath/ASME 2016 Symposium on Fluid Power and Motion Control, ASME Press, 2016, article id V001T01A049Conference paper (Refereed)
    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.

  • 26.
    Freidovich, Leonid
    Michigan State University.
    Constrained joint PD plus controller for flexible link robots2000Conference paper (Refereed)
    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.

  • 27.
    Freidovich, Leonid
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Control methods for robotic applications: lecture notes2013Book (Other academic)
  • 28.
    Freidovich, Leonid B.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Optimal control for linear systems: lecture notes2013Book (Other academic)
  • 29.
    Freidovich, Leonid B.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Gordillo, Francisco
    Departamento de Ingeniería de Sistemas y Automática, Universidad de Sevilla, Sevilla, Spain.
    Shiriaev, Anton
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics. Department of Engineering Cybernetics, Norwegian University of Science and Technology, Trondheim, Norway.
    Gómez-Estern, Fabio
    Departamento de Ingeniería de Sistemas y Automática, Universidad de Sevilla, Spain.
    On generating pre-defined periodic motions in underactuated mechanical systems: The cart-pendulum example2011In: 18th IFAC World Congress, Elsevier, 2011, p. 4588-4593Conference paper (Refereed)
    Abstract [en]

    We study the problem of generating oscillations in underactuated mechanical systems with a chosen time-evolution of some of the generalized coordinates. We consider a classical planar pendulum on a cart example and find conditions of existence of a solution. These conditions are expressed in terms of functions defining synchronization between the actuated and underactuated variables known as virtual holonomic constraints. Explicit expressions for these functions are computed for the cart-pendulum system where the pendulum angle is set to follow a trajectory like a pure sinusoidal waveform around the upright equilibrium. Once the valid virtual constraint has been found with the proposed method, the earlier developed techniques can be applied in order to design an orbitally stabilizing feedback control law. © 2011 IFAC.

  • 30.
    Freidovich, Leonid B.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Shiriaev, Anton
    Department of Engineering Cybernetics, Norwegian University of Science and Technology, Trondheim, Norway.
    Analysis of limit-cycle walking for a compass-like biped robot2010In: 8th IFAC Symposium on Nonlinear Control Systems, Elsevier, 2010, p. 1181-1186Conference paper (Refereed)
    Abstract [en]

    We consider an impulsive mechanical system modeling dynamics of a planar two-link walker commonly known as a compass-gait biped. It is assumed that there is actuation in the hip but that the desired periodic trajectory describes an unstable passive walking gait. We recall and apply a recently developed technique for design of orbitally stabilizing feedback controllers. After that, we illustrate how to assess various properties of the closed-loop system. In particular, sensitivity to perturbations of the slope of the walking surface is analyzed and an estimate for possible deviations from the nominal trajectory is computed analytically. 

  • 31.
    Freidovich, Leonid B.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Shiriaev, Anton S.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics. Department of Engineering Cybernetics, Norwegian University of Science and Technology (NTNU), Trondheim, Norway.
    Transverse linearization for underactuated nonholonomic mechanical systems with application to orbital stabilization2012In: Distributed decision making and control / [ed] Rolf Johansson; Anders Rantzer, London: Springer, 2012, 1, , p. 14p. 245-258Chapter in book (Refereed)
    Abstract [en]

    We consider a class of mechanical systems with an arbitrary number of passive (nonactuated) degrees of freedom, which are subject to a set of nonholonomic constraints. We assume that the challenging problem of motion planning is solved giving rise to a feasible desired periodic trajectory. Our goal is either to analyze orbital stability of this trajectory with a given time-independent feedback control law or to design a stabilizing controller. We extend our previous work done for mechanical systems without nonholonomic constraints. The main contribution is an analytical method for computing coefficients of a linear reduced-order control system, solutions of which approximate dynamics that is transversal to the preplanned trajectory. This linear system is shown to be useful for stability analysis and for design of feedback controllers orbitally, exponentially stabilizing forced periodic motions in nonholonomic mechanical systems.We illustrate our approach on a standard benchmark example.

  • 32.
    Freidovich, Leonid
    et al.
    Michigan State University.
    Khalil, Hassan
    Michigan State University.
    Logic-based switching for robust control of minimum-phase nonlinear systems2005In: Systems & control letters (Print), ISSN 0167-6911, E-ISSN 1872-7956, Vol. 54, no 8, p. 713-727Article in journal (Refereed)
    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.

  • 33.
    Freidovich, Leonid
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Khalil, Hassan
    Michigan State University.
    Logic-based switching for the control of a class of nonlinear systems2003Conference paper (Refereed)
    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.

  • 34.
    Freidovich, Leonid
    et al.
    Michigan State University.
    Khalil, Hassan K.
    Michigan State University.
    Comparison of logic-based switching control designs for a nonlinear system2004In: PROCEEDINGS OF THE 2004 AMERICAN CONTROL CONFERENCE, VOLS 1-6, 2004, p. 1221-1222Conference paper (Refereed)
    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.

  • 35.
    Freidovich, Leonid
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Khalil, Hassan K.
    Michigan State University.
    Lyapunov-based switching control of nonlinear systems using high-gain observers2005In: ACC: Proceedings of the 2005 American Control Conference, Vols 1-7, 2005, p. 5103-5108Conference paper (Refereed)
    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.

  • 36.
    Freidovich, Leonid
    et al.
    Michigan State University.
    Khalil, Hassan K.
    Michigan State University.
    Universal integral controllers for robotic manipulators2002In: Nonlinear control systems 2001: (NOLCOS2001) : a proceeding volume from the 5th IFAC Symposium, St. Petersburg, Russia, 4-6 July 2001, Oxford: Pergamon Press, 2002, p. 351-356Conference paper (Refereed)
    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.

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  • 37.
    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 manipulators1998In: ROBOT CONTROL 1997, VOLS 1 AND 2, 1998, p. 85-90Conference paper (Refereed)
    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.

  • 38.
    Freidovich, Leonid
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Shiriaev, Anton
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Gomez-Estern, Fabio
    Gordillo, Francisco
    Aracil, Javier
    Modification via averaging of partial-energy-shaping control for orbital stabilization: cart-pendulum example2006In: Proceedings of the 45th IEEE conference on decision and control, vols 1-14, New York: IEEE Press, 2006, p. 6150-6155Conference paper (Refereed)
    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.

  • 39.
    Freidovich, Leonid
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    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 pendulum2007In: PROCEEDINGS OF THE 46TH IEEE CONFERENCE ON DECISION AND CONTROL, VOLS 1-14, 2007, p. 1432-1437Conference paper (Refereed)
    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.

  • 40. Guerra, Matteo
    et al.
    Vazquez, Carlos
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Efimov, Denis
    Zheng, Gang
    Freidovich, Leonid
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Perruquetti, Wilfrid
    epsilon-Invariant Output Stabilization: Homogeneous Approach and Dead Zone Compensation2015In: 2015 IEEE 54th Annual Conference on Decision and Control (CDC), 2015, p. 6874-6879Conference paper (Refereed)
    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.

  • 41. Guerra, Matteo
    et al.
    Vazquez, Carlos
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Efimov, Denis
    Zheng, Gang
    Freidovich, Leonid
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Perruquetti, Wilfrid
    Interval Differentiators: on-line estimation of differentiation accuracy2016In: 2016 EUROPEAN CONTROL CONFERENCE (ECC), IEEE, 2016, p. 1347-1352Conference paper (Refereed)
    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.

  • 42.
    Hallén, Mattias
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Comminution control using reinforcement learning: Comparing control strategies for size reduction in mineral processing2018Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    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.

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  • 43.
    Hallén, Mattias
    et al.
    ABB Corporate Research.
    Åstrand, Max
    ABB Corporate Research.
    Sikström, Johannes
    Boliden.
    Servin, Martin
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Reinforcement Learning for Grinding Circuit Control in Mineral Processing2019In: 2019 24th IEEE International Conference on Emerging Technologies and Factory Automation (ETFA), IEEE, 2019, p. 488-495Conference paper (Refereed)
    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.

  • 44.
    Hansson, Anders
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Servin, Martin
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Semi-autonomous shared control of large-scale manipulator arms2010In: Control Engineering Practice, ISSN 0967-0661, E-ISSN 1873-6939, Vol. 18, no 9, p. 1069-1076Article in journal (Refereed)
    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.

  • 45. Ibarra, Luis
    et al.
    Rosales, Antonio
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Ponce, Pedro
    Molina, Arturo
    Adaptive SMC based on the dynamic containment of the sliding variable2021In: Journal of the Franklin Institute, ISSN 0016-0032, E-ISSN 1879-2693, Vol. 358, no 2, p. 1422-1447Article in journal (Refereed)
    Abstract [en]

    Conventional Sliding Mode Controllers (SMCs) exhibit a robust performance against matched bounded uncertainties and disturbances by containing them under a fixed controller's effort. Consequently, the controller is commonly found excessive, leading to chattering and straining the actuator. As a solution, the variable-gain SMCs adapt to the instantaneous system requirements, thus attenuating the aforesaid effects and keeping the SMC's benefits. However, the reported adaptive laws underlying such behavior commonly require arbitrary design considerations and do not consider practical implementation. Unlikely, in this work, a hysteresis-based adaptability law to drive the sliding variable to a boundary layer around zero is proposed. The sliding boundary-hysteresis' width-will consistently "bounce" over the sliding variable, trying to shrink against it while preserving the sliding mode. This behavior finds its steady-state once the sliding variable and the sliding boundary's dynamics are synchronized, with no need of subjective or arbitrary adjustments. The close-loop tuning can be derived from the system's parameters alone, and its steady-state performance can be quantitatively predicted. Furthermore, a method to adjust the sliding surface parameters according to the system's desired behavior is provided, all in a closed, analytical way. Finally, the physical actuator limits are taken into account and never exceeded, and the discrete nature of the devices normally used for SMC implementation is incorporated throughout. Two examples are studied to portray the proposal's advantages.

  • 46. Jonathan Muñoz-Vázquez, Aldo
    et al.
    Vázquez-Aguilera, Carlos
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Parra-Vega, Vicente
    Sánchez-Orta, Anand
    An Exact Robust Differentiator Based on Continuous Fractional Sliding Modes2018In: Journal of Dynamic Systems Measurement, and Control, ISSN 0022-0434, E-ISSN 1528-9028, Vol. 140, no 9, article id 091018Article in journal (Refereed)
    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.

  • 47.
    Keramati, Ehsan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Teimoortashloo, Mazdak
    Department of Electrical Engineering, Azad University of Bojnord, Bojnord, Iran.
    Mohd. Noor, Samsul B.
    Department of Electrical Engineering, University Putra Malaysia, 43400, Malaysia.
    Application of optimized higher order sliding mode control on MEMS optical switch2012In: 12th international workshop on variable structure systems, IEEE, 2012, p. 268-272Conference paper (Refereed)
    Abstract [en]

    MEMS optical switches are used in optical networks in order to provide the desired bandwidth. This paper presents the results of an optimised Higher Order Sliding Mode (HOSM) position controller design. The algorithm requires time derivatives of the sliding variable. A Robust Exact Differentiator is used to estimate time derivatives of the sliding variable. A novel application of Particle Swarm Optimization (PSO) is introduced for optimal tuning of the HOSM controller. Robustness of the controller is investigated and the performance is compared with that obtained by a First Order Sliding Mode (FOSM) controller. 

  • 48.
    Khan, Muhammad Adeel
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Production Code Generation for Rapid Prototyping of Control System using TargetLink2012Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    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.

  • 49.
    Klein, Cristian
    et al.
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Maggio, Martina
    Lund University.
    Årzén, Karl-Erik
    Lund University.
    Hernández-Rodriguez, Francisco
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Brownout: Building More Robust Cloud Applications2014In: 36th International Conference on Software Engineering (ICSE 2014), ACM Digital Library, 2014, p. 700-711Conference paper (Refereed)
    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.

  • 50.
    Klein, Cristian
    et al.
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Maggio, Martina
    Lund University.
    Årzén, Karl-Erik
    Lund University.
    Hernández-Rodriguez, Francisco
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Introducing Service-level Awareness in the Cloud2013Report (Other academic)
    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.

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