liu.seSearch for publications in DiVA
Change search
Refine search result
3456789 251 - 300 of 3893
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • oxford
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 251. Order onlineBuy this publication >>
    Bergman, Kristoffer
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, Faculty of Science & Engineering.
    On Motion Planning Using Numerical Optimal Control2019Licentiate thesis, monograph (Other academic)
    Abstract [en]

    During the last decades, motion planning for autonomous systems has become an important area of research. The high interest is not the least due to the development of systems such as self-driving cars, unmanned aerial vehicles and robotic manipulators. In this thesis, the objective is not only to find feasible solutions to a motion planning problem, but solutions that also optimize some kind of performance measure. From a control perspective, the resulting problem is an instance of an optimal control problem. In this thesis, the focus is to further develop optimal control algorithms such that they be can used to obtain improved solutions to motion planning problems. This is achieved by combining ideas from automatic control, numerical optimization and robotics.

    First, a systematic approach for computing local solutions to motion planning problems in challenging environments is presented. The solutions are computed by combining homotopy methods and numerical optimal control techniques. The general principle is to define a homotopy that transforms, or preferably relaxes, the original problem to an easily solved problem. The approach is demonstrated in motion planning problems in 2D and 3D environments, where the presented method outperforms both a state-of-the-art numerical optimal control method based on standard initialization strategies and a state-of-the-art optimizing sampling-based planner based on random sampling.

    Second, a framework for automatically generating motion primitives for lattice-based motion planners is proposed. Given a family of systems, the user only needs to specify which principle types of motions that are relevant for the considered system family. Based on the selected principle motions and a selected system instance, the algorithm not only automatically optimizes the motions connecting pre-defined boundary conditions, but also simultaneously optimizes the terminal state constraints as well. In addition to handling static a priori known system parameters such as platform dimensions, the framework also allows for fast automatic re-optimization of motion primitives if the system parameters change while the system is in use. Furthermore, the proposed framework is extended to also allow for an optimization of discretization parameters, that are are used by the lattice-based motion planner to define a state-space discretization. This enables an optimized selection of these parameters for a specific system instance.

    Finally, a unified optimization-based path planning approach to efficiently compute locally optimal solutions to advanced path planning problems is presented. The main idea is to combine the strengths of sampling-based path planners and numerical optimal control. The lattice-based path planner is applied to the problem in a first step using a discretized search space, where system dynamics and objective function are chosen to coincide with those used in a second numerical optimal control step. This novel tight combination of a sampling-based path planner and numerical optimal control makes, in a structured way, benefit of the former method’s ability to solve combinatorial parts of the problem and the latter method’s ability to obtain locally optimal solutions not constrained to a discretized search space. The proposed approach is shown in several practically relevant path planning problems to provide improvements in terms of computation time, numerical reliability, and objective function value.

    Download full text (pdf)
    fulltext
    Download (png)
    presentationsbild
  • 252.
    Bergman, Kristoffer
    et al.
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, Faculty of Science & Engineering.
    Axehill, Daniel
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, Faculty of Science & Engineering.
    Combining Homotopy Methods and Numerical Optimal Control to Solve Motion Planning Problems2018In: Proceedings of the 29th IEEE Intelligent Vehicles Symposium, 2018, p. 347-354Conference paper (Refereed)
    Abstract [en]

    This paper presents a systematic approach for computing local solutions to motion planning problems in non-convex environments using numerical optimal control techniques. It extends the range of use of state-of-the-art numerical optimal control tools to problem classes where these tools have previously not been applicable. Today these problems are typically solved using motion planners based on randomized or graph search. The general principle is to define a homotopy that transforms, or preferably relaxes, the original problem to an easily solved problem. In this work, it is shown that by combining a Sequential Quadratic Programming (SQP) method with a homotopy approach that gradually transforms the problem from a relaxed one to the original one, practically relevant locally optimal solutions to the motion planning problem can be computed. The approach is demonstrated in motion planning problems in challenging 2D and 3D environments, where the presented method significantly outperforms both a state-of-the-art numerical optimal control method and a state-of-the-art open-source optimizing sampling-based planner commonly used as benchmark. 

  • 253.
    Bergman, Kristoffer
    et al.
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Ekström, Jonatan
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Modeling, Estimation and Attitude Control of an Octorotor Using PID and L1 Adaptive Control Techniques2014Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    A multirotor is a type of aerial vehicle that has attracted a lot of attention in recent years. Multirotors have found applications in a variety of different fields and they are used by scientists and researchers, commercial UAV companies and radio control enthusiasts alike. In this thesis a multirotor with eight rotors, also called an octorotor, is used.

    A physical model of the octorotor has been developed using theory from rigid body mechanics and aerodynamics. The unknown parameters in this model have been found using several identification experiments. The model has been used for controller design and comparison in a simulation environment.

    An attitude estimation algorithm has been designed and implemented on the target hardware. The algorithm is referred to as a nonlinear complementary filter and it uses a quaternion rotation representation and onboard measurements to compute an estimate of the current aircraft attitude.

    Two different attitude controllers have been designed and evaluated. The first controller is based on PID techniques which are commonly used in multirotor flight stabilization systems. The second controller uses a novel control structure based on L1 adaptive control techniques. A baseline attitude PD controller is augmented with an L1 adaptive controller in the rate feedback loop. The two controller structures are compared using a simulation environment based on the developed model of the octorotor.

    The results show that the proposed structure gives a notable performance increase with respect to robustness against modeling errors and input disturbance rejection compared to the PID controller. However, the L1 adaptive controller is more complex to implement and gives less noise attenuation. The PID controller has been implemented on the platform's hardware and initial flight tests have been performed with promising results.

    Download full text (pdf)
    fulltext
  • 254.
    Bergman, Kristoffer
    et al.
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, Faculty of Science & Engineering.
    Ljungqvist, Oskar
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, Faculty of Science & Engineering.
    Axehill, Daniel
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, Faculty of Science & Engineering.
    Improved Optimization of Motion Primitives for Motion Planning in State Lattices2019In: 2019 30TH IEEE INTELLIGENT VEHICLES SYMPOSIUM (IV19), 2019, p. 2307-2314Conference paper (Refereed)
    Abstract [en]

    In this paper, we propose a framework for generating motion primitives for lattice-based motion planners automatically. Given a family of systems, the user only needs to specify which principle types of motions, which are here denoted maneuvers, that are relevant for the considered system family. Based on the selected maneuver types and a selected system instance, the algorithm not only automatically optimizes the motions connecting pre-defined boundary conditions, but also simultaneously optimizes the end-point boundary conditions as well. This significantly reduces the time consuming part of manually specifying all boundary value problems that should be solved, and no exhaustive search to generate feasible motions is required. In addition to handling static a priori known system parameters, the framework also allows for fast automatic re-optimization of motion primitives if the system parameters change while the system is in use, e.g, if the load significantly changes or a trailer with a new geometry is picked up by an autonomous truck. We also show in several numerical examples that the framework can enhance the performance of the motion planner in terms of total cost for the produced solution.

  • 255.
    Bergman, Nicklas
    et al.
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Larsson, Magnus
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Fault Detection and Isolation in the Water Tank World1998Report (Other academic)
    Abstract [en]

    A flexible, model based fault detection and isolation (FDI) system for an arbitrary configuration of a water tank world has been designed and implemented in MATLAB, SIMULINK and dSPACE. The fault detection is performed with local change detection algorithms, and the fault isolation is performed with residual patterns automatically generated from the total configuration.

    Download full text (pdf)
    fulltext
    Download full text (ps)
    FULLTEXT01
  • 256.
    Bergman, Niclas
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    A Bayesian Approach to Terrain-Aided Navigation1997In: Proceedings of the 11th IFAC Symposium on System Identification, 1997, p. 1531-1536Conference paper (Refereed)
    Abstract [en]

    The terrain-aided navigation problem is a highly nonlinear estimation problem with application to aircraft navigation and missile guidance. In this work the Bayesian approach is used to estimate the aircraft position. With a quantization of the state space an implementable algorithm is found. Problems with low excitation, rough terrain and parallel position hypothesis are handled in a reliable way. The algorithm is evaluated using simulations on real terrain databases.

  • 257.
    Bergman, Niclas
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    A Bayesian Approach to Terrain-Aided Navigation1996Report (Other academic)
    Abstract [en]

    The terrain-aided navigation problem is a highly nonlinear estimation problem with application to aircraft navigation and missile guidance. In this work the Bayesian approach is used to estimate the aircraft position. With a quantization of the state space an implementable algorithm is found. Problems with low excitation, rough terrain and parallel position hypothesis are handled in a reliable way. The algorithm is evaluated using simulations on real terrain databases.

    Download full text (pdf)
    fulltext
    Download full text (ps)
    FULLTEXT01
  • 258.
    Bergman, Niclas
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    A Bayesian Approach to Terrain-Aided Navigation II1997Report (Other academic)
    Abstract [en]

    The terrain-aided navigation problem is a highly nonlinear estimation problem with application to aircraft navigation and missile guidance. In this work the Bayesian approach is used to estimate the aircraft position. With a quantization of the state space an implementable algorithm is found. Problems with low excitation, rough terrain and parallel position hypothesis are handled in a reliable way. The algorithm is evaluated using simulations on real terrain databases.

    Download full text (pdf)
    A Bayesian Approach to Terrain-Aided Navigation II
    Download full text (ps)
    FULLTEXT01
  • 259.
    Bergman, Niclas
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    An Interpolating Wavelet Filter for Terrain Navigation1998In: Proceedings of the First International Conference on Multisource-Multisensor Information Fusion, 1998, p. 251--258Conference paper (Refereed)
    Abstract [en]

    In terrain navigation, traditional aircraft navigation sensors are integrated with a digital terrain map. A promising point-mass algorithm has been applied to the problem in previous work. The algorithm recursively updates the probability of the aircraft position in a finite set of positions in a mesh placed over the map area. It has proven efficient in extensive simulations when the grid mesh is chosen sufficiently dense.

    In order to improve the computational efficiency of the algorithm a novel approach to adaptively choose the grid point positions is presented in this work. Results from wavelet theory and numerical solution of partial differential equations are utilized to adapt the grid mesh on several dyadic scales. Initial tests indicate that the new wavelet filter achieves significant computational performance gains compared to the uniform point-mass version. This fact also makes it applicable to estimation in higer dimension.

  • 260.
    Bergman, Niclas
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Bayesian Inference in Terrain Navigation1997Licentiate thesis, monograph (Other academic)
    Abstract [en]

    Terrain navigation is a concept for autonomous aircraft navigation. If measurements of the terrain height over mean sea-level are collected along the aircraft flight path, an estimate of the aircraft position can be formed by matching these measurements with a digital reference terrain map. This matching is a recursive nonlinear estimation problem. Due to the unstructured nonlinear reference map, local approximation schemes, like the extended Kalman Filter, fail in this application.

    In this work, the optimal Bayesian approach to the recursive inference of the measurement sources is taken. In the Bayesian approach the uncertainty about the aircraft position is condensed in the conditional probability density function. The analytical expression for the recursive propagation of this function is derived.

    Due to the unstructured nonlinear terrain reference map, the propagation of the conditional density is impossible to perform in practice. To circumvent this problem, an approximation of the conditional density is introduced. The recursionis expressed as an update of a set of point-mass weights distributed over an adaptive grid. An efficient implementation of this update is developed.

    In realistic simulations, using a commercial map, the proposed point-mass implementation gives reliable estimates with small estimation errors. The most important feature of the algorithm is the ability to track several position hypotheses in the terrain. A Monte Carlo analysis shows that the filter meets the Cramér-Rao lower bound as the grid resolution increases.

    The Cramér-Rao bound is also utilized to derive an information counterpart of the reference map. This information map reveals the areas where high accuracy navigation can be performed.

    Furthermore, extensions of the point-mass implementation that account for bias errors in the geographic altitude are proposed.

  • 261.
    Bergman, Niclas
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Deterministic and Stochastic Bayesian Methods in Terrain Navigation1998In: Proceedings of the 37th IEEE Conference on Decision and Control, 1998, p. 227-232 vol.1Conference paper (Refereed)
    Abstract [en]

    Terrain navigation is an application where inference between conceptually different sensors is performed recursively online. In this work the Bayesian framework of statistical inference is applied to this recursive estimation problem. Three algorithms for approximative Bayesian estimation are evaluated in simulations, one deterministic algorithm and two stochastic. The deterministic method solve the Bayesian inference problem by numerical integration while the stochastic methods simulate several candidate solutions and evaluates the integral by averaging between these candidates. Simulations show that all three algorithms are efficient and approximately reach the Cramer-Rao bound. However, the stochastic methods are sensitive to outliers and the deterministic method has the limitation of being hard to implement in higher dimensions.

  • 262.
    Bergman, Niclas
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Deterministic and Stochastic Bayesian Methods in Terrain Navigation1998Report (Other academic)
    Abstract [en]

    Terrain navigation is an application where inference between conceptually different sensors is performed recursively online. In this work the Bayesian framework of statistical inference is applied to this recursive estimation problem. Three algorithms for approximative Bayesian estimation are evaluated in simulations, one deterministic algorithm and two stochastic. The deterministic method solve the Bayesian inference problem by numerical integration while the stochastic methods simulate several candidate solutions and evaluates the integral by averaging between these candidates. Simulations show that all three algorithms are efficient and approximately reach the Cramer-Rao bound. However, the stochastic methods are sensitive to outliers and the deterministic method has the limitation of being hard to implement in higher dimensions.

    Download full text (pdf)
    Deterministic and Stochastic Bayesian Methods in Terrain Navigation
    Download full text (ps)
    FULLTEXT01
  • 263.
    Bergman, Niclas
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Expectation Maximization Segmentation1998Report (Other academic)
    Abstract [en]

    This report reviews the Expectation Maximization EM algorithm and applies it to the data segmentation problem yielding the Expectation Maximization Segmentation EMS algorithm The EMS algorithm requires batch processing of the data and can be applied to mode switching or jumping linear dynamical state space models The EMS algorithm consists of an optimal fusion of fixed interval Kalman smoothing and discrete optimization.

    The next section gives a short introduction to the EM algorithm with some background and convergence results In Section the data segmentation problem is dened and in Section the EM algorithm is applied to this problem Section contains simulation results and Section some conclusive remarks.

    Download full text (pdf)
    Expectation Maximization Segmentation
    Download full text (ps)
    FULLTEXT01
  • 264.
    Bergman, Niclas
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    On the Cramer-Rao bound for Terrain-Aided Navigation1997Report (Other academic)
    Download full text (pdf)
    fulltext
    Download full text (ps)
    FULLTEXT01
  • 265.
    Bergman, Niclas
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Recursive Bayesian Estimation: Navigation and Tracking Applications1999Doctoral thesis, monograph (Other academic)
    Abstract [en]

    Recursive estimation deals with the problem of extracting information about parameters, or states, of a dynamical system in real time, given noisy measurements of the system output. Recursive estimation plays a central role in many applications of signal processing, system identification and automatic control. In this thesis we study nonlinear and non-Gaussian recursive estimation problems in discrete time. Our interest in these problems stems from the airborne applications of target tracking, and autonomous aircraft navigation using terrain information.

    In the Bayesian framework of recursive estimation, both the sought parameters and the observations are considered as stochastic processes. The conceptual solution to the estimation problem is found as a recursive expression for the posterior probability density function of the parameters conditioned on the observed measurements. This optimal solution to nonlinear recursive estimation is usually impossible to compute in practice, since it involves several integrals that lack analytical solutions.

    We phrase the application of terrain navigation in the Bayesian framework, and develop a numerical approximation to the optimal but intractable recursive solution. The designed point-mass filter computes a discretized version of the posterior filter density in a uniform mesh over the interesting region of the parameter space. Both the uniform mesh resolution and the grid point locations are automatically adjusted at each iteration of the algorithm. This Bayesian point-mass solution is shown to yield high navigation performance in a simulated realistic environment.

    Even though the optimal Bayesian solution is intractable to implement, the performance of the optimal solution is assessable and can be used for comparative evaluation of suboptimal implementations. We derive explicit expressions for the Cramér-Rao bound of general nonlinear filtering, smoothing and prediction problems. We consider both the cases of random and nonrandom modeling of the parameters. The bounds are recursively expressed and are connected to linear recursive estimation. The newly developed Cramér-Rao bounds are applied to the terrain navigation problem, and the point-mass filter is verified to reach the bound in exhaustive simulations.

    The uniform mesh of the point-mass filter limits it to estimation problems of low dimension. Monte Carlo methods offer an alternative approach to recursive estimation and promise tractable solutions to general high dimensional estimation problems. We provide a review over the active field of statistical Monte Carlo methods. In particular, we study the particle filters for recursive estimation. Three different particle filters are applied to terrain navigation, and evaluated against the Cramér-Rao bound and the point-mass filter. The particle filters utilize an adaptive grid representation of the filter density and are shown to yield a performance equal to the point-mass method.

    A Markov Chain Monte Carlo (MCMC) method is developed for a highly complex data association problem in target tracking. This algorithm is compared to previously proposed methods and is shown to yield competitive results in a simulation study.

  • 266.
    Bergman, Niclas
    et al.
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Gustafsson, Fredrik
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Three Statistical Batch Algorithms for Tracking Manoeuvring Targets1999Report (Other academic)
    Abstract [en]

    The EM algorithm and two MCMC algorithms are applied to manoeuvre detection in target tracking. These statistical methods are off-line and the intended use is to compute upper performance limits of on-line algorithms as well as for off-line analysis. A consequence of the MCMC theory is that an approximation of the a posteriori distribution for the manoeuvre times is obtained.

    Download full text (pdf)
    fulltext
    Download full text (ps)
    FULLTEXT01
  • 267.
    Bergman, Niclas
    et al.
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Ljung, Lennart
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Gustafsson, Fredrik
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Point-Mass Filter and Cramer-Rao Bound for Terrain-Aided Navigation1997Report (Other academic)
    Abstract [en]

    The nonlinear estimation problem in navigation using terrain height variations is studied. The optimal Bayesian solution to the problem is derived. The implementation is grid based, calculating the probability of a set of points on an adaptively dense mesh. The Cramer-Rao bound is derived. Monte Carlo simulations over a commercial map shows that the algorithm, after convergence, reaches the Cramer-Rao lower bound.

    Download full text (pdf)
    fulltext
    Download full text (ps)
    FULLTEXT01
  • 268.
    Bergman, Niclas
    et al.
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Ljung, Lennart
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Gustafsson, Fredrik
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Terrain Navigation using Bayesian Statistics1999In: IEEE Control Systems, ISSN 1066-033X, Vol. 19, no 3, p. 33-40Article in journal (Refereed)
    Abstract [en]

    The performance of terrain-aided navigation of aircraft depends on the size of the terrain gradient in the area. The point-mass filter (PMF) described in this work yields an approximate Bayesian solution that is well suited for the unstructured nonlinear estimation problem in terrain navigation. It recursively propagates a density function of the aircraft position. The shape of the point-mass density reflects the estimate quality; this information is crucial in navigation applications, where estimates from different sources often are fused in a central filter. Monte Carlo simulations show that the approximation can reach the optimal performance, and realistic simulations show that the navigation performance is very high compared with other algorithms and that the point-mass filter solves the recursive estimation problem for all the types of terrain covered in the test. The main advantages of the PMF is that it works for many kinds of nonlinearities and many kinds of noise and prior distributions. The mesh support and resolution are automatically adjusted and controlled using a few intuitive design parameters. The main disadvantage is that it cannot solve estimation problems of very high dimension since the computational complexity of the algorithm increases drastically with the dimension of the state space. The implementation used in this work shows real-time performance for 2D and in some cases 3D models, but higher state dimensions are usually intractable.

  • 269.
    Bergman, Niclas
    et al.
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Ljung, Lennart
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Gustafsson, Fredrik
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Terrain Navigation using Bayesian Statistics1999Report (Other academic)
    Abstract [en]

    In aircraft navigation the demands on reliability and safety are very high. The importance of accurate position and velocity information becomes crucial when flying an aircraft at low altitudes, and especially during the landing phase. Not only should the navigation system have a consistent description of the position of the aircraft, but also a description of the surrounding terrain, buildings and other objects that are close to the aircraft. Terrain navigation is a navigation scheme that utilizes variations in the terrain height along the aircraft flight path. Integrated with an Inertial Navigation System (INS), it yields high performance position estimates in an autonomous manner, ie without any support information sent to the aircraft. In order to obtain these position estimates, a nonlinear recursive estimation problem must be solved on-line. Traditionally, this filtering problem has been solved by local linearization of the terrain at one or several assumed aircraft positions. Due to changing terrain characteristics, these linearizations will in some cases result in diverging position estimates. In this work, we show how the Bayesian approach gives a comprehensive framework for solving the recursive estimation problem in terrain navigation. Instead of approximating the model of the estimation problem, the analytical solution is approximately implemented. The proposed navigation filter computes a probability mass distribution of the aircraft position and updates this description recursively with each new measurement. The navigation filter is evaluated over a commercial terrain database, yielding accurate position estimates over several types of terrain characteristics. Moreover, in a Monte Carlo analysis, it shows optimal performance as it reaches the Cramér-Rao lower bound.

    Download full text (pdf)
    FULLTEXT01
  • 270.
    Bergmark, Anders
    Linköping University, Department of Electrical Engineering.
    Reglering av klinkerugn för framställning av zinkklinker2005Independent thesis Basic level (professional degree), 20 points / 30 hpStudent thesis
    Abstract [en]

    In the fuming plant at Rönnskärsverken smelter, zinc clinker is xtracted from slags and steel mill dust. In the fuming furnace, zinc and lead are vapourised by coal injection. The reoxidised metal dust is further refined at the clinker plant to obtain a product that is low in halogenes. Zinc clinker, which contains approximately 70 - 75 % zinc, is exported to the Norzink zinc smelter in Norway. The refinement takes place in an industrial kiln. The kiln is a very slow system and therefore difficult to control which results in disturbances and dead time. This causes low production rate and poor quality in the clinker. In order to cope with this, automatic control is tested in this thesis. Two process models have been built for simulation and control design and three controllers have been evaluated in simulation. Two of the developed controllers are tested on the actual process. A framework for fast controller prototyping has also been developed. A C++-class för communication using the DDE interface between controller and the operator user interface has also been implemented.

    Download full text (pdf)
    FULLTEXT01
  • 271.
    Bergström, Andreas
    et al.
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, Faculty of Science & Engineering. Ericsson Research.
    Hendeby, Gustaf
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, Faculty of Science & Engineering.
    Gunnarsson, Fredrik
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, Faculty of Science & Engineering. Ericsson Research.
    Gustafsson, Fredrik
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, Faculty of Science & Engineering.
    TOA Estimation Improvements in Multipath Environments by Measurement Error Models2017In: Proceedings of the 2017 IEEE 28th Annual International Symposium on Personal, Indoor, and Mobile Radio Communications (PIMRC), Institute of Electrical and Electronics Engineers (IEEE), 2017, p. 1-8Conference paper (Refereed)
    Abstract [en]

    Many positioning systems rely on accuratetime of arrival measurements. In this paper, we addressnot only the accuracy but also the relevance of Time ofArrival (TOA) measurement error modeling. We discusshow better knowledge of these errors can improve relativedistance estimation, and compare the impact of differentlydetailed measurement error information. These models arecompared in simulations based on models derived froman Ultra Wideband (UWB) measurement campaign. Theconclusion is that significant improvements can be madewithout providing detailed received signal information butwith a generic and relevant measurement error model.

    Download full text (pdf)
    TOA Estimation Improvements in Multipath Environments by Measurement Error Models
  • 272.
    Bernhard, Jacob
    et al.
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Johansson, Patrik
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Advanced control of a remotely operated underwater vehicle2012Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Remotely Operated underwater Vehicles (ROVs) are getting more and more advanced withevery new model. As new functionality is added, the price increases. This thesis is one partof a larger project, where the goal is to develop a low-budget ROV. The ROV should later bemade autonomous and entered into a competition.This thesis have focused on the modeling and stabilizing control of an ROV that was designedby mechanical engineering students at Linköping University. The only sensor used was anInertial Measurement Unit (IMU) and the ROV has a torpedo-like design. The modeling wasdone using identification in Matlab with the grey box and black box methods. Water trialsand simulations show that the model is estimated sufficiently good to be used as the basis ofdifferent model based controllers.Two different control strategies were implemented; a linear quadratic controller (LQ) and amodel predictive controller (MPC). Both controllers worked desirably in simulations. Onlythe LQ controller was evaluated in real world tests. Due to problems with the implementationenvironment chosen for the MPC, the MPC could not be tested.The thesis also uses decision matrices as a mean to motivate the important decisions thathave been made.

    Download full text (pdf)
    Advanced control of a remotely operated underwater vehicle (2012)
  • 273.
    Besselmann, Thomas
    et al.
    ABB, Switzerland .
    Löfberg, Johan
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Morari, Manfred
    ETH Zürich, Switzerland .
    Explicit MPC for LPV Systems: Stability and Optimality2012In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 57, no 9, p. 2322-2332Article in journal (Refereed)
    Abstract [en]

    This paper considers high-speed control of constrained linear parameter-varying systems using model predictive control. Existing model predictive control schemes for control of constrained linear parameter-varying systems typically require the solution of a semi-definite program at each sampling instance. Recently, variants of explicit model predictive control were proposed for linear parameter-varying systems with polytopic representation, decreasing the online computational effort by orders of magnitude. Depending on the mathematical structure of the underlying system, the constrained finite-time optimal control problem can be solved optimally, or close-to-optimal solutions can be computed. Constraint satisfaction, recursive feasibility and asymptotic stability can be guaranteed a priori by an appropriate selection of the terminal state constraints and terminal cost. The paper at hand gathers previous developments and provides new material such as a proof for the optimality of the solution, or, in the case of close-to-optimal solutions, a procedure to determine a bound on the suboptimality of the solution.

    Download full text (pdf)
    fulltext
  • 274.
    Betshammar, Jan
    Linköping University, Department of Electrical Engineering.
    Improved Billet Shape Modeling in Optimization of the Hot Rod and Wire Rolling Process2006Independent thesis Basic level (professional degree), 20 points / 30 hpStudent thesis
    Abstract [en]

    The hot rod and wire rolling process is widely used to produce rolled iron alloys in different shapes and dimensions. This industry has been under a constant development during the last decades. Today, complex geometries are produced at a high speed since it is possible to use several stands in each mill at the same time. A reason for the development is rising demands from customers. The most important demands are to save energy, to get better material properties and higher dimension accuracy. To meet these demands on speed and accuracy, a better control of how the material behaves in the process is needed. There is also a need to be able to quickly find a new setup of the mill in order to be able to produce other geometries.

    The purpose with this Master Thesis is to model and simulate the hot rod and wire rolling process with the modeling language Modelica. The model is given the known inputs and the desired final result in order to compute the unknown inputs to the mill. To meet these goals, a model that depends on for example the gap between the rolls, the roll speeds and the tensions between different stands is needed. It should be possible to make simulations to find roll speeds or to calculate the tensions caused by known roll speeds.

    With the help of models of the steps in the process, a model has been developed in Modelica. The model can be expanded to a mill with an arbitrary number of stands. In the search for the best way of modeling a hot rod and wire rolling mill, several algorithms have been simulated and analyzed in Modelica. The results from all simulations show that the billet and the groove should be described by different functions for the upper and the lower half. Furthermore, it is not a good solution to use only polynomials to describe the shapes in the process. A function with infinite derivative in the endpoints is needed to describe the billet in an acceptable way. The problem has also been solved using Matlab. In this work it is shown that the Modelica solution is preferred, compared to solving the optimization problems in Matlab. An advantage with the Modelica solution is that the model can be split into several easily connected sub models. Unfortunately it was even hard for Modelica to solve general problems. The describing functions made it hard to find the intersections and to keep the area constant during the rotation. The least square method could lead to bad approximations of the shapes.

    Download full text (pdf)
    FULLTEXT01
  • 275.
    Birgestam, Magnus
    Linköping University, Department of Management and Engineering.
    Controlling a Robot Hand in Simulation and Reality2008Independent thesis Advanced level (degree of Magister), 20 points / 30 hpStudent thesis
    Abstract [en]

    This master thesis was made at the Institute of Technology Stockholm and is a part of a robot hand project called 10-X with the aim to develop a low-cost robot hand that is light and strong.

    The project specification is to further improve the ability to control the robot hand in a user friendly way. This has been done by implementing a controller, earlier used and developed at KTH, which is intuitive and easy to customize after the needs in different kinds of grasps. To make the controller easy to use an user interface has been made.

    Before the implementation of the controller was made on the real hand it was tested and development on a simulation created in MATLAB/simulink with help from a graphic physics engine called GraspIt! The movement of the robot finger is effected of the force from a leaf spring and a tendon that bends the finger. Also the finger is exposed of contact forces and all these components had to be modeled in the simulation to make the finger act properly.

    Download full text (pdf)
    FULLTEXT01
  • 276.
    Björk, Ylva
    et al.
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Wilhelmsson, Ebba
    Linköping University, Department of Electrical Engineering. Linköping University, The Institute of Technology.
    Linearisation of micro loudspeakers using adaptive control2014Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Loudspeakers were invented over 150 years ago, but the loudspeakers used todayare still based on the same ideas. Traditionally, good sound quality has been obtainedby using expensive materials in the loudspeakers and by allowing themto be big. However, nowadays loudspeakers are wanted in applications such asmobile phones and tablets where size and weight are very limited and there is aconstant desire to decrease production costs. Special small loudspeakers, knownas micro loudspeakers, have been developed for this purpose but due to the severerestrictions in size and manufacturing costs, the sound quality in the microloudspeakers is relatively poor. One problem is that the nonlinearities of thesystem, present in any loudspeaker, become more evident in the case of microloudspeakers and cause noticeable distortion of the sound.This master’s thesis has been performed in cooperation with Opalum (formerlyActiwave), a company specializing in using digital signal processing to improvethe sound in loudspeakers with poor acoustic properties. The objective of thethesis is to investigate ways to increase the sound quality in micro loudspeakersby using nonlinear control. Focus has been on frequencies below the resonancefrequency since the distortion is more noticeable at low frequencies. First, a nonlinearmodel of the micro loudspeaker has been obtained using system identificationstrategies. The model describes the relationship between the voltage overthe voice-coil and the diaphragm displacement. Subsequently, input-output linearisationhas been used to design a controller for the system and the effect onthe distortion has been investigated through experiments. Two different modelstructures have been tested, a physical model based on the Thiele-Small modeland a black-box model with a Hammerstein-Wiener structure. In both cases, thenonlinearities were modelled as polynomials. The controller was then extendedwith an updating algorithm, making it adaptive.The efficiency of the controllers has been proved by experiments, where distortionwas decreased by up to 60 % compared to the case without control. The effectwas largest for low frequencies, around one third of the resonance frequency,but improvements were noted up to about two thirds of the resonance frequency,depending on the loudspeaker unit. The approach using a physical model andthat using a black-box model have shown similar results.

    Download full text (pdf)
    fulltext
  • 277.
    Björklund, Fredrik
    et al.
    Linköping University, Department of Electrical Engineering, Vehicular Systems.
    Karlström, Elin
    Linköping University, Department of Electrical Engineering, Vehicular Systems.
    Enabling Testing of Lateral Active Safety Functions in a Multi-rate Hardware in the Loop Environment2017Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    As the development of vehicles moves towards shorter development time, new ways of verifying the vehicle performance is needed in order to begin the verification process at an earlier stage. A great extent of this development regards active safety, which is a collection name for systems that help both avoid accidents and minimize the effects of a collision, e.g brake assist and steering control systems. Development of these active safety functions requires extensive testing and verification in order to guarantee the performance of the functions in different situations. One way of testing these functions is to include them in a Hardware in the Loop simulation, where the involved hardware from the real vehicle are included in the simulation loop.

    This master thesis investigates the possibility to test lateral active safety functions in a hardware in the loop simulation environment consisting of multiple subsystems working on different frequencies. The subsystems are all dependent of the output from other subsystems, forming an algebraic loop between them. Simulation using multiple hardware and subsystems working on different frequencies introduces latency in the simulation. The effect of the latency is investigated and proposed solutions are presented. In order to enable testing of lateral active safety functions, a steering model which enables the servo motor to steer the vehicle is integrated in the simulation environment and validated.

    Download full text (pdf)
    fulltext
  • 278.
    Björklund, Svante
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    A Study of the Choice of Model Orders in Arxstruc-Type Methods for Open-Loop Time-Delay Estimation in Linear Systems2003Report (Other academic)
    Abstract [en]

    In this report we study estimation of time-delays in linear dynamical systems with additive noise. Estimating time-delays is a common engineering problem, e.g. in automatic control, system identification and signal processing. The purpose with this work is to test and evaluate a certain class of methods for time-delay estimation, especially with automatic control applications in mind. The principle of the methods in the class is to estimate several discrete-time models of a certain model structure with different explicit time-delays. The estimated time-delay is the time-delay whose model has the lowest mean square difference between the true and estimated output signal. The methods are evaluated experimentally with the aid of simulations and plots of RMS error and confidence intervals for different cases.The results are: The output error (OE) model structure has the lowest RMS error but is very slow. Low model orders give the best result. The ARX model structure has a higher RMS error but is very fast. High model orders give the best result. An ARX model structure with prefiltered input and output signals was also tested. It has an RMS error that is nearly as good as for the OE model structure and is fast but not as fast as the unfiltered ARX. The best model orders are high for the denominator polynomial and low for the numerator polynomial.

    Download full text (pdf)
    FULLTEXT01
  • 279.
    Björklund, Svante
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    A Survey and Comparison of Time-Delay Estimation Methods in Linear Systems2003Licentiate thesis, monograph (Other academic)
    Abstract [en]

    In this thesis the problem of time-delay estimation (TDE) in linear dynamic systems is treated. The TDE is studied for signal-to-noise ratios, input signals, and systems that are common in process industry. This also implies that both open-loop and closed-loop cases are of interest. The true time-delay is estimated, which may be different from the time-delay giving the best model approximation of the true system. Time-delays which are not a multiple of the sampling interval are also of interest to estimate.

    In this thesis, a review and a classification according to underlying principles of TDE methods in the literature are made. The main classes are: 1) Time-Delay Approximation Methods: The time-delay is estimated from a relation (a model) between the input and output signals expressed in a certain basis. The time-delay is not an explicit parameter in the model. 2) Explicit Time-Delay Parameter Methods: The time-delay is an explicit parameter in the model. 3) Area and Moment Methods: The time-delay is estimated from certain integrals of the impulse and step responses. 4) Higher Order Statistics Methods.

    Some new methods and variants of old ones are suggested and evaluated, some of which have good estimation performance and some poor performance. Properties of TDE methods are analyzed, both theoretically and experimentally. Recommendations are given on how to choose estimation method and input signal. Generally, prediction error methods where the time-delay parameter is explicit and is optimized simultaneously with the other model parameters give good estimation quality.

    Most evaluations have been conducted with factorial experiments using Monte Carlo simulations in open and closed loop. Some statistical analysis methods have been utilized: The RMS error of the time-delay estimates gives an absolute measure of the performance. ANOVA (ANalysis Of VAriance) and confidence intervals give conclusions with a certain level of confidence.

  • 280.
    Björklund, Svante
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Analysis of a Phase Method for Time-Delay Estimation2002Report (Other academic)
    Abstract [en]

    In this report we study estimation of time delays in linear dynamical systems with additive noise. Estimating the time delay is a common engineering problem, e.g. in automatic control, system identification and signal processing.This report reviews and analyzes a certain time-delay estimation method: A discrete-time model of a continuous-time system is identified. The non-minimum phase zeros form the allpass part of the model. The dead-time is estimated by looking at the slope at low frequencies of the phase of the allpass part. We have experimentally studied the estimation method with the help of simulations in open loop and closed loop. We have looked at the estimates, poles, zeros and the phase. We have also performed statistical analyses with RMS (root mean square) error plots and with confidence interval calculations. Our results show that the estimation method can be used with several different model structures of the discrete-time model. The estimation method is, however, non-robust and can totally fail in some cases. The probability of failure depends on the used model structure, the input signal type and the signal-to-noise ratio. The estimation method can be made more robust by removing false non-minimum phase zeros, caused by the noise, in a certain way. It is usually better not to prewhite the data applied to the estimation method. For input (reference) signals of the form of steps, the Laguerre model structure seems to be an appropriate choice in open (closed) loop.

    Download full text (pdf)
    FULLTEXT01
  • 281.
    Björklund, Svante
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Analysis of a Phase Method for Time-Delay Estimation. Short Version.2003Report (Other academic)
    Abstract [en]

    In this report, estimation of time delays in linear dynamical systems with additive noise is studied. The report reviews and analyses a certain estimation method: A discrete-time model of a continuous-time system is identified. The non-minimum phase zeros form the allpass part of the model. The dead-time is estimated by the slope at low frequencies of the phase of the allpass part. The method has been experimentally studied with the aid of simulations in open and closed loop. The results show that the estimation method can be used with several different model structures. The method is, however, non-robust and can totally fail in some cases. The probability of failure depends on the model structure, the input signal type and the signal-to-noise ratio. The estimation method can be made more robust by removing false non-minimum phase zeros, caused by the noise, in a certain way. It is usually better not to prewhite the data applied to the method.

    Download full text (pdf)
    FULLTEXT01
  • 282.
    Björklund, Svante
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Experimental Evaluation of some Cross Correlation Methods for Time-Delay Estimation in Linear Systems2003Report (Other academic)
    Abstract [en]

    In this report we study estimation of time-delays in linear dynamical systems with additive noise. Estimating time-delays is a common engineering problem, e.g. in automatic control, system identification and signal processing.We have experimentally studied cross correlation methods for time-delay estimation in order to find the "best" method or if none is best which method to use in different situations. We have simulated systems with time-delay and studied internal quantities of the methods, the time-delay estimates, RMS-errors of estimates, percentage of failed estimates, Analysis of Variance (ANOVA) and confidence intervals for different cases. Our result is that no method is always best but one method is clearly inferior to the other. The methods can be divided in two groups with similar properties: thresholding methods and area and moment methods. The thresholding methods work better for fast systems than slow systems whereas the area and moment methods works better for slow systems than fast. The thresholding methods work better with random binary input signals than steps as input whereas the area and moment methods works better with steps as input than random binary input.

    Download full text (pdf)
    FULLTEXT01
  • 283.
    Björklund, Svante
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Experimental Evaluation of some Methods using Simple Process Models for Estimating Continuous Time-Delays in Open-Loop2003Report (Other academic)
    Abstract [en]

    In this report we study estimation of time-delays in linear dynamical systems with additive noise. Estimating time-delays is a common engineering problem, e.g. in automatic control, system identification and signal processing. The purpose with this work is to test and evaluate a certain class of methods for time-delay estimation, especially with automatic control applications in mind. The class of methods consists of estimating the time-delay as a continuous parameter with a prediction error method in some simple model structures which are often used in process industry. The methods are evaluated experimentally with the aid of simulations and plots of RMS error, bias, standard deviation and confidence intervals for different cases.The results are: It is best not to prewhite the input signal. There should be at the most one real pole in the model structure. In some cases the simplest model structure, a first order system with time-delay "idproc6", is clearly the best. It is not clearly worse than the best in any case. The RMS error varies much with the system, the input signal type and the SNR. For idproc6 it varies between 0.3 and 12.1 sampling intervals in the performed simulations with a mean of 4.7.

    Download full text (pdf)
    FULLTEXT01
  • 284.
    Björklund, Svante
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Experimental Evaluation of some Thresholding Methods for Estimating Time-Delays in Open-Loop2003Report (Other academic)
    Abstract [en]

    In this report we study estimation of time-delays in linear dynamical systems with additive noise. Estimating time-delays is a common engineering problem, e.g. in automatic control, system identification and signal processing. The purpose with this work is to test and evaluate a certain class of methods for time-delay estimation, especially with automatic control applications in mind. Particularly interesting it is to determine the best method. Is one method best in all situations or should different methods be used for different situations? The tested class of methods consists essentially of thresholding the cross correlation between the output and input signals. This is a very common method for time-delay estimation. The methods are tested and evaluated experimentally with the aid of simulations and plots of RMS error, bias and confidence intervals. The results are: The methods often miss to detect because the threshold is too high. The threshold has nevertheless been selected to give the best result. All methods over-estimate the time-delay. Nearly the whole RMS error is due to the bias. None of the tested methods is always best. Which method is best depends on the system and what is done when missing detections. Some form of averaging of the cross correlation, e.g. integration to step response or CUSUM, is advantageous. Fast systems are easiest. White noise input signal is easiest and steps is hardest. The RMS-errors are high in average (approximately greater than 6 sampling intervals). The error is lower for fast system or for high SNR.

    Download full text (pdf)
    FULLTEXT01
  • 285.
    Björklund, Svante
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Experimental Open-Loop Evaluation of some Time-Delay Estimation Methods in the Laguerre Domain2003Report (Other academic)
    Abstract [en]

    In this report we study estimation of time-delays in linear dynamical systems with additive noise. Estimating time-delays is a common engineering problem, e.g. in automatic control, system identification and signal processing. The purpose with this work is to test and evaluate a certain class of methods for time-delay estimation, especially with automatic control applications in mind. The class of methods consists of estimating the time-delay from the Laguerre transform of the input and output signals. The methods are evaluated experimentally with the aid of simulations and plots of approximation error, plots of original and Laguerre approximated input and output signals, plots of estimates, plots of RMS error, tables of ANOVA and plots of confidence intervals for different cases. The results are: Only certain input signals, e.g. steps, are useful. Systems with a not too fast dynamics give better estimation quality than pure time-delay systems despite the fact that the estimation methods were derived for pure time-delay systems. The Laguerre pole should be chosen in a certain way. The number of Laguerre functions should be as a high as possible.

    Download full text (pdf)
    FULLTEXT01
  • 286.
    Björklund, Svante
    et al.
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Ljung, Lennart
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    A Review of Time-Delay Estimation Techniques2003In: Proceedings of the 42nd IEEE Conference on Decision and Control, 2003, p. 2502-2507 vol.3Conference paper (Refereed)
    Abstract [en]

    This paper reviews and evaluates suggested methods for estimating the time-delay of linear systems in automatic control applications. A classification of the methods according to the underlying principles is suggested. The evaluation, done by analyzing the estimates of the methods from extensive simulated data in open loop, shows that different classes of methods have different properties and are suitable in different cases. Some method are clearly inferior to others. Recommendations are given on how to choose estimation method and input signal.

  • 287.
    Björklund, Svante
    et al.
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Ljung, Lennart
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    A Review of Time-Delay Estimation Techniques2003Report (Other academic)
    Abstract [en]

    This paper reviews and evaluates suggested methods for estimating the time-delay of linear systems in automatic control applications. A classification of the methods according to the underlying principles is suggested. The evaluation, done by analyzing the estimates of the methods from extensive simulated data in open loop, shows that different classes of methods have different properties and are suitable in different cases. Some method are clearly inferior to others. Recommendations are given on how to choose estimation method and input signal.

    Download full text (pdf)
    FULLTEXT01
  • 288.
    Björklund, Svante
    et al.
    Linköping University, Department of Electrical Engineering. Linköping University, The Institute of Technology. Swedish Defence Research Agency, Sweden.
    Ljung, Lennart
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    An Improved Phase Method for Time-Delay Estimation2010Report (Other academic)
    Abstract [en]

    A promising method for estimation of the time-delay in continuous-time linear dynamical systems uses the phase of the all-pass part of a discrete-time model of the system. We have discovered that this method can sometimes fail totally and we suggest a method for avoiding such failures.

    Download full text (pdf)
    FULLTEXT01
  • 289.
    Björklund, Svante
    et al.
    Swedish Defence Research Agency, Sweden.
    Ljung, Lennart
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    An Improved Phase Method for Time-Delay Estimation2009In: Automatica, ISSN 0005-1098, E-ISSN 1873-2836, Vol. 45, no 10, p. 2467-2470Article in journal (Refereed)
    Abstract [en]

    A promising method for estimation of the time-delay in continuous-time linear dynamical systems uses the phase of the all-pass part of a discrete-time model of the system. We have discovered that this method can sometimes fail totally and we suggest a method for avoiding such failures.

  • 290.
    Björklund, Svante
    et al.
    Swedish Defence Research Agency (FOI).
    Petersson, Henrik
    Swedish Defence Reserearch Agency (FOI).
    Hendeby, Gustaf
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology. Linköping University, Faculty of Science & Engineering.
    Features for micro-Doppler based activity classification2015In: IET radar, sonar & navigation, ISSN 1751-8784, E-ISSN 1751-8792, Vol. 9, no 9, p. 1181-1187Article in journal (Refereed)
    Abstract [en]

    Safety and security applications benefit from better situational awareness. Radar micro-Doppler signatures from an observed target carry information about the target's activity, and have potential to improve situational awareness. This article describes, compares, and discusses two methods to classify human activity based on radar micro-Doppler data. The first method extracts physically interpretable features from the time-velocity domain such as the main cycle time and properties of the envelope of the micro-Doppler spectra and use these in the classification. The second method derives its features based on the components with the most energy in the cadence-velocity domain (obtained as the Fourier transform of the time-velocity domain). Measurements from a field trial show that the two methods have similar activity classification performance. It is suggested that target base velocity and main limb cadence frequency are indirect features of both methods, and that they do often alone suffice to discriminate between the studied activities. This is corroborated by experiments with a reduced feature set. This opens up for designing new more compact feature sets. Moreover, weaknesses of the methods and the impact of non-radial motion are discussed.

    Download full text (pdf)
    fulltext
  • 291.
    Björklund, Svante
    et al.
    Swedish Defence Research Agency (FOI), Linköping, Sweden.
    Petersson, Henrik
    Swedish Defence Research Agency (FOI), Linköping, Sweden.
    Hendeby, Gustaf
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology. Swedish Defence Research Agency (FOI), Linköping, Sweden.
    On distinguishing between human individuals in micro-Doppler signatures2013In: 14th International Radar Symposium (IRS), 2013, p. 865-870Conference paper (Refereed)
    Abstract [en]

    Radar micro-Doppler signatures (MDS) of humans are created by movements of body parts, such as legs and arms. MDSs can be used in security applications to detect humans and classify their type and activity. Target association and tracking, which can facilitate the classification, become easier if it is possible to distinguish between human individuals by their MDSs. By this we mean to recognize the same individual in a short time frame but not to establish the identity of the individual. In this paper we perform a statistical experiment in which six test persons are able to distinguish between walking human individuals from their MDSs. From this we conclude that there is information in the MDSs of the humans to distinguish between different individuals, which also can be used by a machine. Based on the results of the best test persons we also discuss features in the MDSs that could be utilized to make this processing possible.

  • 292.
    Björkman, Mattias
    et al.
    ABB, Sweden.
    Brogårdh, Torgny
    ABB, Sweden.
    Hanssen, Sven
    ABB, Sweden.
    Lindström, Sven-Erik
    ABB, Sweden.
    Moberg, Stig
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Norrlöf, Mikael
    Linköping University, The Institute of Technology. Linköping University, Department of Electrical Engineering, Automatic Control.
    A New Concept for Motion Control of Industrial Robots2008In: Proceedings of the 17th IFAC World Congress, 2008Conference paper (Refereed)
    Abstract [en]

    This paper gives a short summary of an industrial development work on model-based motion control. This development has resultet in high robot motion performance simultaneously with an efficient use of the installed drive system of the robot.

  • 293.
    Björkman, Mattias
    et al.
    ABB, Sweden.
    Brogårdh, Torgny
    ABB, Sweden.
    Hanssen, Sven
    ABB, Sweden.
    Lindström, Sven-Erik
    ABB, Sweden.
    Moberg, Stig
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Norrlöf, Mikael
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    A New Concept for Motion Control of Industrial Robots2008Report (Other academic)
    Abstract [en]

    This paper gives a short summary of an industrial development work on model-based motion control. This development has resultet in high robot motion performance simultaneously with an efficient use of the installed drive system of the robot.

    Download full text (pdf)
    FULLTEXT01
  • 294.
    Björsson, Anders
    Linköping University, Department of Electrical Engineering.
    Simulation analysis of RLC/MAC for UMTS in Network Simulator version 22004Independent thesis Basic level (professional degree)Student thesis
    Abstract [en]

    The Internet has mainly been interconnecting stationary computers by wired links, but an increasing number of mobile clients require wireless communication. One way to connect these clients is to use the Universal Mobile Telecommunication System, UMTS. UMTS is a third generation mobile system.

    A network can be seen as nodes interconnected by links. The functionality of the nodes can be described as a layered hierarchy. A reference model for this hierarchy was developed by OSI. In this model the second lowest layer is called data link layer. The data link layer is responsible for making the raw transmission appear error free to upper layers.

    The focus for this thesis is the data link layer in the UMTS. Compared to the data link layer in a wired scenario it contains more control and error correction mechanisms. These mechanisms use a lot of timers and triggers, which makes it very difficult to analyze them mathematically. Therefore simulation is the preferred method.

    For the simulations the network simulator version 2 was used. This is an open source discrete event simulator. It has a modularized wireless stack already implemented. This can not be used to simulate UMTS though. Some modules in this stack were replaced by a new implementation to make simulations on UMTS possible.

    Tests were performed on the new implementation and the results were what could be expected. The results were also consistent with previous research in the area.

    Download full text (pdf)
    FULLTEXT01
  • 295.
    Blaszak, Maciej
    et al.
    Adam Mickiewicz University, Poland.
    Marciniak, Krzysztof
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Classical and Quantum Superintegrability of Stackel Systems2017In: SIGMA. Symmetry, Integrability and Geometry, ISSN 1815-0659, E-ISSN 1815-0659, Vol. 13, article id 008Article in journal (Refereed)
    Abstract [en]

    In this paper we discuss maximal superintegrability of both classical and quantum Stackel systems. We prove a sufficient condition for a flat or constant curvature Stackel system to be maximally superintegrable. Further, we prove a sufficient condition for a Stackel transform to preserve maximal superintegrability and we apply this condition to our class of Stackel systems, which yields new maximally superintegrable systems as conformal deformations of the original systems. Further, we demonstrate how to perform the procedure of minimal quantization to considered systems in order to produce quantum superintegrable and quantum separable systems.

    Download full text (pdf)
    fulltext
  • 296.
    Bleser, Gabriele
    et al.
    Department Augmented Vision, German Research Center for Artificial Intelligence, Kaiserslautern, Germany; Department of Computer Science, Technical University of Kaiserslautern, Kaiserslautern, Germany.
    Damen, Dima
    Department of Computer Science, University of Bristol, Bristol, UK.
    Behera, Ardhendu
    School of Computing, University of Leeds, Leeds, UK; Department of Computing, Edge Hill University, Ormskirk, UK.
    Hendeby, Gustaf
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Mura, Katharina
    SmartFactory KL e.V., Kaiserslautern, Germany.
    Miezal, Markus
    Department of Computer Science, Technical University of Kaiserslautern, Kaiserslautern, Germany.
    Gee, Andrew
    Department of Computer Science, University of Bristol, Bristol, UK.
    Petersen, Nils
    Department Augmented Vision, German Research Center for Artificial Intelligence, Kaiserslautern, Germany.
    Maçães, Gustavo
    Department Computer Vision, Interaction and Graphics, Center for Computer Graphics, Guimarães, Portugal.
    Domingues, Hugo
    Department Computer Vision, Interaction and Graphics, Center for Computer Graphics, Guimarães, Portugal.
    Gorecky, Dominic
    SmartFactory KL e.V., Kaiserslautern, Germany.
    Almeida, Luis
    Department Computer Vision, Interaction and Graphics, Center for Computer Graphics, Guimarães, Portugal.
    Mayol-Cuevas, Walterio
    Department of Computer Science, University of Bristol, Bristol, UK.
    Calway, Andrew
    Department of Computer Science, University of Bristol, Bristol, UK.
    Cohn, Anthony G.
    School of Computing, University of Leeds, Leeds, UK.
    Hogg, David C.
    School of Computing, University of Leeds, Leeds, UK.
    Stricker, Didier
    Department Augmented Vision, German Research Center for Artificial Intelligence, Kaiserslautern, Germany.
    Cognitive Learning, Monitoring and Assistance of Industrial Workflows Using Egocentric Sensor Networks2015In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 10, no 6, article id e0127769Article in journal (Refereed)
    Abstract [en]

    Today, the workflows that are involved in industrial assembly and production activities are becoming increasingly complex. To efficiently and safely perform these workflows is demanding on the workers, in particular when it comes to infrequent or repetitive tasks. This burden on the workers can be eased by introducing smart assistance systems. This article presents a scalable concept and an integrated system demonstrator designed for this purpose. The basic idea is to learn workflows from observing multiple expert operators and then transfer the learnt workflow models to novice users. Being entirely learning-based, the proposed system can be applied to various tasks and domains. The above idea has been realized in a prototype, which combines components pushing the state of the art of hardware and software designed with interoperability in mind. The emphasis of this article is on the algorithms developed for the prototype: 1) fusion of inertial and visual sensor information from an on-body sensor network (BSN) to robustly track the user’s pose in magnetically polluted environments; 2) learning-based computer vision algorithms to map the workspace, localize the sensor with respect to the workspace and capture objects, even as they are carried; 3) domain-independent and robust workflow recovery and monitoring algorithms based on spatiotemporal pairwise relations deduced from object and user movement with respect to the scene; and 4) context-sensitive augmented reality (AR) user feedback using a head-mounted display (HMD). A distinguishing key feature of the developed algorithms is that they all operate solely on data from the on-body sensor network and that no external instrumentation is needed. The feasibility of the chosen approach for the complete action-perception-feedback loop is demonstrated on three increasingly complex datasets representing manual industrial tasks. These limited size datasets indicate and highlight the potential of the chosen technology as a combined entity as well as point out limitations of the system.

    Download full text (pdf)
    fulltext
  • 297.
    Bleser, Gabriele
    et al.
    German Research Center for Artificial Intelligence, Kaiserslautern, Germany.
    Hendeby, Gustaf
    German Research Center for Artificial Intelligence, Kaiserslautern, Germany.
    Using optical flow for filling the gaps in visual-inertial tracking2010Conference paper (Refereed)
    Abstract [en]

    Egomotion tracking is since the last decades an often addressed problem and hybrid approaches evidentially have potential to provide accurate, efficient and robust results. Simultaneous localisation and mapping (SLAM) - in contrast to a model-based approach - is used to enable tracking in unknown environments. However, it also suffers from high computational complexity. Moreover, in many applications, the map itself is not needed and the target environment is partiall known, e.g. in a few 3D anchor points. In this paper, rather than using SLAM, optical flow measurements are introduced into a model-based system. With these measurements, a modified visual-inertial tracking method is derived, which in Monte Carlo simulations reduces the need for 3D points and thus allows tracking during extended gaps of 3D point registrations.

  • 298.
    Bleser, Gabriele
    et al.
    German Research Center for Artificial Intelligence (DFKI), Kaiserslautern, Germany.
    Steffen, Daniel
    German Research Center for Artificial Intelligence (DFKI), Kaiserslautern, Germany.
    Reiss, Attila
    ACTLab, University of Passau, 94032, Passau, Germany.
    Weber, Markus
    German Research Center for Artificial Intelligence (DFKI), Kaiserslautern, Germany.
    Hendeby, Gustaf
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Fradet, Laetitia
    Université de Poitiers, 86000, Poitiers, France.
    Personalized Physical Activity Monitoring Using Wearable Sensors2015In: Smart Health: Open Problems and Future Challenges / [ed] Andreas Holzinger, Carsten Röcker, Martina Ziefle, Springer International Publishing , 2015, p. 99-124Chapter in book (Refereed)
    Abstract [en]

    It is a well-known fact that exercising helps people improve their overall well-being; both physiological and psychological health. Regular moderate physical activity improves the risk of disease progression, improves the chances for successful rehabilitation, and lowers the levels of stress hormones. Physical fitness can be categorized in cardiovascular fitness, and muscular strength and endurance. A proper balance between aerobic activities and strength exercises are important to maximize the positive effects. This balance is not always easily obtained, so assistance tools are important. Hence, ambient assisted living (AAL) systems that support and motivate balanced training are desirable. This chapter presents methods to provide this, focusing on the methodologies and concepts implemented by the authors in the physical activity monitoring for aging people (PAMAP) platform. The chapter sets the stage for an architecture to provide personalized activity monitoring using a network of wearable sensors, mainly inertial measurement units (IMU). The main focus is then to describe how to do this in a personalizable way: (1) monitoring to provide an estimate of aerobic activities performed, for which a boosting based method to determine activity type, intensity, frequency, and duration is given; (2) supervise and coach strength activities. Here, methodologies are described for obtaining the parameters needed to provide real-time useful feedback to the user about how to exercise safely using the right technique.

  • 299.
    Bleser, Gabriele
    et al.
    German Research Center for Artificial Intelligence (DFKI), Kaiserslautern, Germany.
    Steffen, Daniel
    German Research Center for Artificial Intelligence (DFKI), Kaiserslautern, Germany.
    Weber, Markus
    German Research Center for Artificial Intelligence (DFKI), Kaiserslautern, Germany.
    Hendeby, Gustaf
    Linköping University, The Institute of Technology. Linköping University, Department of Electrical Engineering, Automatic Control.
    Stricker, Didier
    German Research Center for Artificial Intelligence (DFKI), Kaiserslautern, Germany.
    Fradet, Laetitia
    Université de Technologie de Compiègne, France.
    Marin, Frédéric
    Université de Technologie de Compiègne, France.
    Ville, Nathalie
    CIC-IT Inserm 804, Rennes, France.
    Carré, Francois
    CIC-IT Inserm 804, Rennes, France.
    A personalized exercise trainer for the elderly2013In: Journal of Ambient Intelligence and Smart Environments, ISSN 1876-1364, E-ISSN 1876-1372, Vol. 5, no 6, p. 547-562Article in journal (Refereed)
    Abstract [en]

    Regular and moderate physical activity practice provides many physiological benefits. It reduces the risk of disease outcomes and is the basis for proper rehabilitation after a severe disease. Aerobic activity and strength exercises are strongly recommended in order to maintain autonomy with ageing. Balanced activity of both types is important, especially to the elderly population. Several methods have been proposed to monitor aerobic activities. However, no appropriate method is available for controlling more complex parameters of strength exercises. Within this context, the present article introduces a personalized, home-based strength exercise trainer designed for the elderly. The system guides a user at home through a personalized exercise program. Using a network of wearable sensors the user's motions are captured. These are evaluated by comparing them to prescribed exercises, taking both exercise load and technique into account. Moreover, the evaluation results are immediately translated into appropriate feedback to the user in order to assist the correct exercise execution. Besides the direct feedback, a major novelty of the system is its generic personalization by means of a supervised teach-in phase, where the program is performed once under supervision of a physical activity specialist. This teach-in phase allows the system to record and learn the correct execution of exercises for the individual user and to provide personalized monitoring. The user-driven design process, the system development and its underlying activity monitoring methodology are described. Moreover, technical evaluation results as well as results concerning the usability of the system for ageing people are presented. The latter has been assessed in a clinical study with thirty participants of 60 years or older, some of them showing usual diseases or functional limitations observed in elderly population.

    Download full text (pdf)
    fulltext
  • 300.
    Blom, Jonas
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Power Control in Cellular Radio Systems1998Licentiate thesis, monograph (Other academic)
    Abstract [en]

    The primary goal of cellular radio systems, is to provide communication services to a large number of mobile users. Due to the rapid expansion of the market in this area, the available resources have to be used efficiently. The main issue in this thesis is methods to assign appropriate transmission powers, given coarsely quantized measurements, in order to meet the quality requirements from the users despite various disturbances.

    We propose a concept of a power regulator comprising the steps of estimating relevant quantities, handling quality specications, and controlling the powers. With this setting, the power controlling component relates directly to the mainstream of the algorithms proposed to date.

    For practical reasons, it is necessary to control the powers in a distributed fashion, and these distributed algorithms can be seen as local control loops. The effects of time delays and power output constraints in these loops are analyzed with respect to stability, using root locus techniques and describing functions. We emphasize the importance of identifying these time delays and constraints in order to choose the appropriate controller parameters for stable operation. The relevance of the local stability results on the overall system level is discussed, and further analyzed in a simulation environment, which has been developed.

    The literature is surveyed, and the contributions are classified with respect to a common framework in order to stress their similarities and differences. We show that an integrating controller forms the basis for the most popular algorithms. Methods for convergence analysis are investigated and related to the theory of linear systems. These methods are applied when proving global convergence of the integrating controller.

    The power control strategies are evaluated under more realistic circumstances in an environment simulating the operation of a GSM system. Comparing the results when using different power control algorithms we note that the proposed concept performs better than the algorithms proposed to date, both in terms of transmission quality of service and capacity.

3456789 251 - 300 of 3893
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • oxford
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf