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• 201.
Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology. Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
Tool Position Estimation of a Flexible Industrial Robot using Recursive Bayesian Methods2011Report (Other academic)

A sensor fusion method for state estimation of a flexible industrial robot is presented. By measuring the acceleration at the end-effector, the accuracy of the arm angular position is improved significantly when these measurements are fused with motor angle observation. The problem is formulated in a Bayesian estimation framework and two solutions are proposed; one using the extended Kalman filter (EKF) and one using the particle filter (PF). The technique is verified on experiments on the ABB IRB4600 robot, where the accelerometer method is showing a significant better dynamic performance, even when model errors are present.

Tool Position Estimation of a Flexible Industrial Robot using Recursive Bayesian Methods
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• 202.
Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
Estimation of Orientation and Position of an Accelerometer Mounted to an Industrial Manipulator2011Report (Other academic)

A method to find the orientation and position of a three degree-of-freedom (DOF) accelerometer mounted on a six DOF industrial robot is proposed and evaluated on experimental data. The method consists of two consecutive steps, where the first is to estimate the orientation of the sensor using data from static experiments. In the second step the sensor position relative to the robot base is identified using sensor readings when the sensor moves in a circular path and where the sensor orientation is kept constant in a path fixed coordinate system.  Once the accelerometer position and orientation are identified it is possible to use the sensor in robot model parameter identification and in advanced control solutions.

Estimation of Orientation and Position of an Accelerometer Mounted to an Industrial Manipulator
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• 203.
Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
Method to Estimate the Position and Orientation of a Triaxial Accelerometer Mounted to an Industrial Manipulator2012In: Proceedings of the 10th IFAC Symposium on Robot Control, 2012, p. 283-288Conference paper (Refereed)

A novel method to find the orientation and position of a triaxial accelerometer mounted on a six degrees-of-freedom industrial robot is proposed and evaluated on experimental data. The method consists of two consecutive steps, where the first is to estimate the orientation of the accelerometer from static experiments. In the second step the accelerometer position relative to the robot base is identified using accelerometer readings when the accelerometer moves in a circular path and where the accelerometer orientation is kept constant in a path fixed coordinate system. Once the accelerometer position and orientation are identified it is possible to use the accelerometer in robot model parameter identification and in advanced control solutions. Compared to previous methods, the accelerometer position estimation is completely new, whereas the orientation is found using an analytical solution to the optimisation problem. Previous methods use a parameterisation where the optimisation uses an iterative solver.

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• 204.
Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
Method to Estimate the Position and Orientation of a Triaxial Accelerometer Mounted to an Industrial Manipulator2011Report (Other academic)

A novel method to find the orientation and position of a triaxial accelerometer mounted on a six degrees-of-freedom industrial robot is proposed and evaluated on experimental data. The method consists of two consecutive steps, where the first is to estimate the orientation of the accelerometer from static experiments. In the second step the accelerometer position relative to the robot base is identified using accelerometer readings when the accelerometer moves in a circular path and where the accelerometer orientation is kept constant in a path fixed coordinate system. Once the accelerometer position and orientation are identified it is possible to use the accelerometer in robot model parameter identification and in advanced control solutions. Compared to previous methods, the accelerometer position estimation is completely new, whereas the orientation is found using an analytical solution to the optimisation problem. Previous methods use a parameterisation where the optimisation uses an iterative solver.

Method to Estimate the Position and Orientation of a Triaxial Accelerometer Mounted to an Industrial Manipulator
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• 205.
Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology. Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology. Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
Extended Kalman Filter Applied to Industrial Manipulators2010In: Proceedings of Reglermöte 2010, 2010Conference paper (Other academic)

This paper summarizes previous work on tool position estimation on industrial manipulators, and emphasize the problems that must be taken care of in order to get a satisfied result. The acceleration of the robot tool, measured by an accelerometer, together with measurements of motor angles are used. The states are estimated with an extended Kalman filter. A method for tuning the covariance matrices for the noise, used in the observer, is suggested. The work has been focused on a robot with two degrees of freedom.

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• 206.
Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology. Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology. Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
ML Estimation of Process Noise Variance in Dynamic Systems2010Report (Other academic)

The performance of a non-linear filter hinges in the end on the accuracy of the assumed non-linear model of the process. In particular, the process noise covariance $Q$ is hard to get by physical modeling and dedicated system identification experiments. We propose a variant of the expectation maximization (EM) algorithm which iteratively estimates the unobserved state sequence and $Q$ based on the observations of the process. The extended Kalman smoother (EKS) is the instrument to find the unobserved state sequence. Our contribution fills a gap in literature, where previously only the linear Kalman smoother and particle smoother have been applied. The algorithm will be important for future industrial robots with more flexible structures, where the particle smoother cannot be applied due to the high state dimension. The proposed method is compared to two alternative methods on a simulated robot.

ML Estimation of Process Noise Variance in Dynamic Systems
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• 207.
Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology. Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology. Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
ML Estimation of Process Noise Variance in Dynamic Systems2011In: Proceedings of the 18th IFAC World Congress, 2011, p. 5609-5614Conference paper (Refereed)

The performance of a non-linear filter hinges in the end on the accuracy of the assumed non-linear model of the process. In particular, the process noise covariance Q is hard to get by physical modeling and dedicated system identification experiments. We propose a variant of the expectation maximization (EM) algorithm which iteratively estimates the unobserved state sequence and Q based on the observations of the process. The extended Kalman smoother (EKS) is the instrument to find the unobserved state sequence. Our contribution fills a gap in literature, where previously only the linear Kalman smoother and particle smoother have been applied. The algorithm will be important for future industrial robots with more flexible structures, where the particle smoother cannot be applied due to the high state dimension. The proposed method is compared to two alternative methods on a simulated robot.

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• 208.
Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
Katholieke Universiteit, Leuven, Belgium. Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology. Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
H Synthesis Method for Control of Non-linear Flexible Joint Models2013Report (Other academic)

An H synthesis method for control of a flexible joint, with non-linear spring characteristic, is proposed. The first step of the synthesis method is to extend the joint model with an uncertainty description of the stiffness parameter. In the second step, a non-linear optimisation problem, based on nominal performance and robust stability requirements, has to be solved. Using the Lyapunov shaping paradigm and a change of variables, the non-linear optimisation problem can be rewritten as a convex, yet conservative, LMI problem. The method is motivated by the assumption that the joint operates in a specific stiffness region of the non-linear spring most of the time, hence the performance requirements are only valid in that region. However, the controller must stabilise the system in all stiffness regions. The method is validated in simulations on a non-linear flexible joint model originating from an industrial robot.

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• 209.
Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
Katholieke Universiteit, Leuven, Belgium. Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology. Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
H Synthesis Method for Control of Non-linear Flexible Joint Models2014In: Proceedings of the 19th IFAC World Congress, 2014 / [ed] Boje, Edward and Xia, Xiaohua, International Federation of Automatic Control , 2014, p. 8372-8377Conference paper (Refereed)

An H synthesis method for control of a flexible joint, with non-linear spring characteristic, is proposed. The first step of the synthesis method is to extend the joint model with an uncertainty description of the stiffness parameter. In the second step, a non-linear optimisation problem, based on nominal performance and robust stability requirements, has to be solved. Using the Lyapunov shaping paradigm and a change of variables, the non-linear optimisation problem can be rewritten as a convex, yet conservative, LMI problem. The method is motivated by the assumption that the joint operates in a specific stiffness region of the non-linear spring most of the time, hence the performance requirements are only valid in that region. However, the controller must stabilise the system in all stiffness regions. The method is validated in simulations on a non-linear flexible joint model originating from an industrial robot.

H∞ Synthesis Method for Control of Non-linear Flexible Joint Models
• 210.
Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, The Institute of Technology.
Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology. Swedish Air Force Combat Simulation Center at the Swedish Defence Research Agency. Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, The Institute of Technology. Human Systems Integration Division at NASA Ames Research Center. Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, The Institute of Technology.
Accuracy of Eyepoint Estimation in Optical See-Through Head-Mounted Displays Using the Single Point Active Alignment Method2011Conference paper (Other academic)

This paper studies the accuracy of the estimated eyepoint of an Optical See-Through Head-Mounted Display (OST HMD) calibrated using the Single Point Active Alignment Method (SPAAM). Quantitative evaluation of calibration procedures for OST HMDs is complicated as it is currently not possible to share the subject’s view. Temporarily replacing the subject’s eye with a camera during the calibration or evaluation stage has been proposed, but the uncertainty of a correct eyepoint estimation remains. In the experiment reported in this paper, subjects were used for all stages of calibration and the results were verified with a 3D measurement device. The nine participants constructed 25 visual alignments per calibration after which the estimated pinhole camera model was decomposed into its intrinsic and extrinsic parameters using two common methods. Unique to this experiment, compared to previous evaluations, is the measurement device used to cup the subject’s eyeball. It measures the eyepoint location relative to the head tracker, thereby establishing the calibration accuracy of the estimated eyepoint location. As the results on accuracy are expressed as individual pinhole camera parameters, rather than a compounded registration error, this paper complements  previously published work on parameter variance as the former denotes bias and the latter represents noise. Results indicate that the calibrated eyepoint is on average 5 cm away from its measured location and exhibits a vertical bias which potentially causes dipvergence for stereoscopic vision for objects located further away than 5.6 m. Lastly, this paper closes with a discussion on the suitability of the traditional pinhole camera model for OST HMD calibration.

• 211.
Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, The Institute of Technology.
Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology. Swedish Defence Research Agency. Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, The Institute of Technology. NASA Ames Research Center. Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, The Institute of Technology.
Parameter Estimation Variance of the Single Point Active Alignment Method in Optical See-Through Head Mounted Display Calibration2011In: Proceedings of the IEEE Virtual Reality Conference / [ed] Michitaka Hirose, Benjamin Lok, Aditi Majumder and Dieter Schmalstieg, Piscataway, NJ, USA: IEEE , 2011, p. 27-24Conference paper (Refereed)

The parameter estimation variance of the Single Point Active Alignment Method (SPAAM) is studied through an experiment where 11 subjects are instructed to create alignments using an Optical See-Through Head Mounted Display (OSTHMD) such that three separate correspondence point distributions are acquired. Modeling the OSTHMD and the subject's dominant eye as a pinhole camera, findings show that a correspondence point distribution well distributed along the user's line of sight yields less variant parameter estimates. The estimated eye point location is studied in particular detail. Thefindings of the experiment are complemented with simulated datawhich show that image plane orientation is sensitive to the numberof correspondence points. The simulated data also illustrates someinteresting properties on the numerical stability of the calibrationproblem as a function of alignment noise, number of correspondencepoints, and correspondence point distribution.

• 212.
Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology, Visual Information Technology and Applications (VITA).
Optical See-Through Head Mounted Display: Direct Linear Transformation Calibration Robustness in the Presence of User Alignment Noise2010Report (Other academic)

The correct spatial registration between virtual and real objects in optical see-through augmented reality implies accurate estimates of the user’s eyepoint relative to the location and orientation of the display surface. A common approach is to estimate the display parameters through a calibration procedure involving a subjective alignment exercise. Human postural sway and targeting precision contribute to imprecise alignments, which in turn adversely affect the display parameter estimation resulting in registration errors between virtual and real objects. The technique commonly used has its origin incomputer vision, and calibrates stationary cameras using hundreds of correspondence points collected instantaneously in one video frame where precision is limited only by pixel quantization and image blur. Subsequently the input noise level is several order of magnitudes greater when a human operator manually collects correspondence points one by one. This paper investigates the effect of human alignment noise on view parameter estimation in an optical see-through head mounted display to determine how well astandard camera calibration method performs at greater noise levels than documented in computer vision literature. Through Monte-Carlo simulations we show that it is particularly difficult to estimate the user’s eyepoint in depth, but that a greater distribution of correspondence points in depth help mitigate the effects of human alignment noise.

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• 213.
Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, The Institute of Technology.
Optical See-Through Head Mounted Display: Direct Linear Transformation Calibration Robustness in the Presence of User Alignment Noise2010In: Proceedings of the 54th Annual Meeting of the Human Factors and Ergonomics Society, 2010Conference paper (Refereed)

The correct spatial registration between virtual and real objects in optical see-through augmented reality implies accurate estimates of the user’s eyepoint relative to the location and orientation of the display surface. A common approach is to estimate the display parameters through a calibration procedure involving a subjective alignment exercise. Human postural sway and targeting precision contribute to imprecise alignments, which in turn adversely affect the display parameter estimation resulting in registration errors between virtual and real objects. The technique commonly used has its origin incomputer vision, and calibrates stationary cameras using hundreds of correspondence points collected instantaneously in one video frame where precision is limited only by pixel quantization and image blur. Subsequently the input noise level is several order of magnitudes greater when a human operator manually collects correspondence points one by one. This paper investigates the effect of human alignment noise on view parameter estimation in an optical see-through head mounted display to determine how well astandard camera calibration method performs at greater noise levels than documented in computer vision literature. Through Monte-Carlo simulations we show that it is particularly difficult to estimate the user’s eyepoint in depth, but that a greater distribution of correspondence points in depth help mitigate the effects of human alignment noise.

• 214.
Universidade Federal de Minas Gerais, Brazil.
Robotics and Motion Division, ABB AB. Robotics and Motion Division, ABB AB. Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, Faculty of Science & Engineering.
Failure detection in robotic arms using  statistical modeling, machine learning and hybrid gradient boosting2018Report (Other academic)

Modeling and failure prediction is an important task in manyengineering systems. For this task, the machine learning literaturepresents a large variety of models such as classification trees,random forest, artificial neural networks, fuzzy systems, amongothers. In addition, standard statistical models can be applied suchas the logistic regression, linear discriminant analysis, $k$-nearestneighbors, among others. This work evaluates advantages andlimitations of statistical and machine learning methods to predictfailures in industrial robots. The work is based on data from morethan five thousand robots in industrial use. Furthermore, a newapproach combining standard statistical and machine learning models,named \emph{hybrid gradient boosting}, is proposed. Results show thatthe a priori treatment of the database, i.e., outlier analysis,consistent database analysis and anomaly analysis have shown to becrucial to improve classification performance for statistical, machinelearning and hybrid models. Furthermore, local joint information hasbeen identified as the main driver for failure detection whereasfailure classification can be improved using additional informationfrom different joints and hybrid models.

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• 215.
Univ Toulouse Isae Supaero, France.
Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, Faculty of Science & Engineering. Middle East Tech Univ, Turkey. Univ Toulouse Isae Supaero, France.
A TIGHTER BAYESIAN CRAMER-RAO BOUND2019In: 2019 IEEE INTERNATIONAL CONFERENCE ON ACOUSTICS, SPEECH AND SIGNAL PROCESSING (ICASSP), IEEE , 2019, p. 5277-5281Conference paper (Refereed)

It has been shown lately that any "standard" Bayesian lower bound (BLB) on the mean squared error (MSE) of the Weiss-Weinstein family (WWF) admits a "tighter" form which upper bounds the "standard" form. Applied to the Bayesian Cramer-Rao bound (BCRB), this result suggests to redefine the concept of efficient estimator relatively to the tighter form of the BCRB, an update supported by a noteworthy example. This paper lays the foundation to revisit some Bayesian estimation problems where the BCRB is not tight in the asymptotic region.

• 216.
University of Toulouse - ISAE-Supaero.
Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, Faculty of Science & Engineering. Middle East Technical University, Turkey. University of Toulouse - ISAE-Supaero.
Some Inequalities Between Pairs of Marginal and Joint Bayesian Lower Bounds2019In: Proc. of 22nd International Conference on Information Fusion (FUSION), 2019, p. 1-8Conference paper (Refereed)

In this paper, tightness relations (or inequalities) between Bayesian lower bounds (BLBs) on the mean-squared-error are derived which result from the marginalization of a joint probability density function (pdf) depending on both parameters of interest and extraneous or nuisance parameters. In particular,it is shown that for a large class of BLBs, the BLB derived from the marginal pdf is at least as tight as the corresponding BLB derived from the joint pdf. A Bayesian linear regression example is used to illustrate the tightness relations

• 217.
Slovak Univ. of Tech. in Bratislava, Slovakia.
Slovak Univ. of Tech. in Bratislava, Slovakia. Slovak Univ. of Tech. in Bratislava, Slovakia. Slovak Univ. of Tech. in Bratislava, Slovakia. Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, Faculty of Science & Engineering. Slovak Univ. of Tech. in Bratislava, Slovakia.
Explicit MPC Based on Approximate Dynamic Programming2018In: 2018 EUROPEAN CONTROL CONFERENCE (ECC), 2018Conference paper (Refereed)

In this paper we show how to synthesize simple explicit MPC controllers based on approximate dynamic programming. Here, a given MPC optimization problem over a finite horizon is solved iteratively as a series of problems of size one. The optimal cost function of each subproblem is approximated by a quadratic function that serves as a cost-to-go function for the subsequent iteration. The approximation is designed in such a way that closed-loop stability and recursive feasibility is maintained. Specifically, we show how to employ sum-of-squares relaxations to enforce that the approximate cost-to-go function is bounded from below and from above for all points of its domain. By resorting to quadratic approximations, the complexity of the resulting explicit MPC controller is considerably reduced both in terms of memory as well as the on-line computations. The procedure is applied to control an inverted pendulum and experimental data are presented to demonstrate viability of such an approach.

• 218.
University of Politecn Cataluna, Spain.
Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, Faculty of Science & Engineering.
Drug combinatorics and side effect estimation on the signed human drug-target network2016In: BMC Systems Biology, ISSN 1752-0509, E-ISSN 1752-0509, Vol. 10, no 74Article in journal (Refereed)

Background: The mode of action of a drug on its targets can often be classified as being positive (activator, potentiator, agonist, etc.) or negative (inhibitor, blocker, antagonist, etc.). The signed edges of a drug-target network can be used to investigate the combined mechanisms of action of multiple drugs on the ensemble of common targets. Results: In this paper it is shown that for the signed human drug-target network the majority of drug pairs tend to have synergistic effects on the common targets, i.e., drug pairs tend to have modes of action with the same sign on most of the shared targets, especially for the principal pharmacological targets of a drug. Methods are proposed to compute this synergism, as well as to estimate the influence of the drugs on the side effect of another drug. Conclusions: Enriching a drug-target network with information of functional nature like the sign of the interactions allows to explore in a systematic way a series of network properties of key importance in the context of computational drug combinatorics.

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• 219.
Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, Department of Computer and Information Science, UASTECH - Autonomous Unmanned Aircraft Systems Technologies.
Localization algorithms for indoor UAVs2011Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis

The increased market for navigation, localization and mapping system has encouraged the research to dig deeper into these new and challenging areas. The remarkable development of computer soft- and hardware have also opened up many new doors. Things which more or less where impossible ten years ago are now reality.

The possibilities of using a mathematical approach to compensate for the need of expensive sensors has been one of the main objectives in this thesis. Here you will find the basic principles of localization of indoor UAVs using particle filter (PF) and Octomaps, but also the procedures of implementing 2D scanmatching algorithms and quaternions. The performance of the algorithms is evaluated using a high precision motion capture system. The UAV which forms the basis for this thesis is equipped with a 2D laser and an inertial measurement unit (IMU). The results show that it is possible to perform localization in 2D with centimetre precision only by using information from a laser and a predefined Octomap.

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• 220.
Royal Institute of Technology, Sweden.
Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology. Royal Institute of Technology, Sweden. Royal Institute of Technology, Sweden.
Gain Estimation for Hammerstein Systems2006In: Proceedings of the 14th IFAC Symposium on System Identification, 2006, p. 784-789Conference paper (Refereed)

In this paper, we discuss and compare three different approaches for L2-gain estimation of Hammerstein systems. The objective is to find the input signal that maximizes the gain. A fundamental difference between two of the approaches is the class, or structure, of the input signals. The first approach involves describing functions and therefore the class of input signals is sinusoids. In this case we assume that we have a model of the system and we search for the amplitude and frequency that give the largest gain. In the second approach, no structure on the input signal is assumed in advance and the system does not have to be modelled first. The maximizing input is found using an iterative procedure called power iterations. In the last approach, a new iterative procedure tailored for memoryless nonlinearities is used to find the maximizing input forthe unmodelled nonlinear part of the Hammerstein system. The approaches are illustrated by numerical examples.

• 221.
Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
Model Predictive Control of a Tricopter2012Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis

In this master thesis, a real-time control system that stabilizes the rotational rates of a tri-copter, has been studied. The tricopter is a rotorcraft with three rotors.

The tricopter has been modelled and identified, using system identification algorithms. The model has been used in a Kalman filter to estimate the state of the system and for design ofa model based controller.

The control approach used in this thesis is a model predictive controller, which is a multi-variable controller that uses a quadratic optimization problem to compute the optimal con-trol signal. The problem is solved subject to a linear model of the system and the physicallimitations of the system.

Two different types of algorithms that solves the MPC problem have been studied. These are explicit MPC and the fast gradient method. Explicit MPC is a pre-computed solution to the problem, while the fast gradient method is an online solution.

The algorithms have been simulated with the Kalman filter and were implemented on themicrocontroller of the tricopter.

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• 222.
Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
Asymptotic Efficiency of CCA Subspace Methods in the Case of no Exogenous Inputs2000Report (Other academic)

In this paper one of the main open questions in the area of subspace methods is answered partly. One particular algorithm, sometimes termed CCA, is shown to be asymptotically equivalent to estimates obtained by minimizing the pseudo maximum likelihood. Here asymptotically equivalent means, that the difference of the two estimators times the square root of the sample size tends to zero.

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• 223.
Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
On Data Preprocessing for Subspace Methods2000In: Proceedings of the 39th IEEE Conference on Decision and Control, IEEE , 2000, Vol. 3, p. 2403-2408Conference paper (Refereed)

In modern data analysis often the first step is to perform some data preprocessing, e.g. detrending or elimination of periodic components of known period length. This is normally done using least squares regression. Only afterwards black box models are estimated using either pseudo-maximum-likelihood methods, prediction error methods or subspace algorithms. In this paper it is shown, that for subspace methods this is essentially the same as including the corresponding input variables, e.g. a constant or a trend or a periodic component, as additional input variables. Here essentially means, that the estimates only dier through the choice of initial values.

• 224.
Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
On Data Preprocessing for Subspace Methods2000Report (Other academic)

In modern data analysis often the first step is to perform some data preprocessing, e.g. detrending or elimination of periodic components of known period length. This is normally done using least squares regression. Only afterwards black box models are estimated using either pseudo-maximum-likelihood methods, prediction error methods or subspace algorithms. In this paper it is shown, that for subspace methods this is essentially the same as including the corresponding input variables, e.g. a constant or a trend or a periodic component, as additional input variables. Here essentially means, that the estimates only dier through the choice of initial values.

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• 225.
Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
Order Estimation for Subspace Methods2000Report (Other academic)

In this paper the question of estimating the order in the context of subspace methods is addressed. Three different approaches are presented and the asymptotic properties there of derived. Two of these methods are based on the information contained in the estimated singular values, while the third method is based on the estimated innovation variance. The case with observed inputs is treated as well as the case without exogenous inputs. The two methods based on the singular values are shown to be consistent under fairly mild assumptions, while the same result for the thirf approach is only obtained on a subset. The former can be applied to Larimore type of procedures as well as to MOESP type of procedures, where as the latter is only applied to Larimore type of algorithms. This has implications for the estimation of the order of systems, which are close to the exceptional set, as is shown in a numerical example. All the estimation methods involve the choice of a penalty term. Sufficient copnditions on the penalty term to guarantee consistency are derived. The effects of different choices of the penalty term are investigated in a simulation study.

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• 226.
Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology. Vienna University of Technology, Austria.
Order Estimation for Subspace Methods2001In: Automatica, ISSN 0005-1098, E-ISSN 1873-2836, Vol. 37, no 10, p. 1561-1573Article in journal (Refereed)

Three different order estimation criteria in the context of subspace algorithms are introduced and sufficient conditions for strong consistency are derived. A simulation study points to open questions.

• 227.
Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
Some facts about the Choice of the Weighting Matrices in Larimore Type of Subspace Algorithms2000Report (Other academic)

In this paper the effect of some weighting matrices on the asymptotic variance of the estimates of linear discrete time state space systems estimated using subspace methods is investigated. The analysis deals with systems with white or without observed inputs and refers to the Larimore type of subspace procedures. The main result expresses the asymptotic variance of the system matrix estimates in canonical form as a function of some of the user choices, clarifying the question on how to choose them optimally. It is shown, that the CCA weighting scheme leads to optimal accuracy. The expressions for the asymptotic variance can be implemented more efficiently as compared to the ones previously published.

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• 228.
Institute F. Econometrics, Austria.
Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
Some Facts about the Choice of the Weighting Matrices in Larimore Type of Subspace Algorithms2002In: Automatica, ISSN 0005-1098, E-ISSN 1873-2836, Vol. 38, no 5, p. 763-773Article in journal (Refereed)

In this paper the effect of some weighting matrices on the asymptotic variance of the estimates of linear discrete time state space systems estimated using subspace methods is investigated. The analysis deals with systems with white or without observed inputs and refers to the Larimore type of subspace procedures. The main result expresses the asymptotic variance of the system matrix estimates in canonical form as a function of some of the user choices, clarifying the question on how to choose them optimally. It is shown, that the CCA weighting scheme leads to optimal accuracy. The expressions for the asymptotic variance can be implemented more efficiently as compared to the ones previously published.

• 229.
Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
University of Newcastle, Australia.
Asymptotic properties of Hammerstein model estimates2000In: Proceedings of the 39th IEEE Conference on Decision and Control, 2000Conference paper (Refereed)

This paper considers the estimation of Hammerstein models with input saturation. These models are characterised by a linear dynamical model acting on an input sequence which is affected by a hard saturation of unknown level. The main result of the paper lies in a specication of a set of sufficient conditions on the input sequence in order to ensure that a non-linear least-squares approach enjoys properties of consistency and asymptotic normality and furthermore, that an estimate of the parameter covariance matrix is also consistent. The set of assumptions is specied using the concept of near epoch dependence, which has been developed in the econometrics literature. Indeed, one purpose of this paper is to highlight the usefulness of this concept in the context of analysing estimation procedures for nonlinear dynamical systems.

• 230.
Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
Department of Electrical and Computer Engineering University of Newcastle, Australia.
Asymptotic Properties of Identification of Hammerstein Models with Input Saturation2000Report (Other academic)

This paper considers the estimation of Hammerstein models with input saturation. These models are characterised by a linear dynamical model acting on an input sequence which is affected by a hard saturation of unknown level. The main result of the paper lies in a specication of a set of sufficient conditions on the input sequence in order to ensure that a non-linear least-squares approach enjoys properties of consistency and asymptotic normality and furthermore, that an estimate of the parameter covariance matrix is also consistent. The set of assumptions is specied using the concept of near epoch dependence, which has been developed in the econometrics literature. Indeed, one purpose of this paper is to highlight the usefulness of this concept in the context of analysing estimation procedures for nonlinear dynamical systems.

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• 231.
Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
University of Berne, Switzerland.
Subspace Algorithm Cointegration Analysis - an Application to Interest Rate Data2000In: Proceedings of the 39th IEEE Conference on Decision and Control, 2000, p. 146-151Conference paper (Refereed)

In this paper the application of so called subspace methods for the specication and estimation of cointegrated systems is examined. This method, which is based on the state space representation, is suited for the analysis of general cointegrated systems of order one, i.e. is not limited to autoregressive models, as is e.g. Johansen's method. To assess the empirical usefulness of the method we apply it to perform a cointegration analysis of the US term structure of interest rates.

• 232.
Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
University of Berne, Switzerland.
Subspace Algorithm Cointegration Analysis - an Application to Interest Rate Data2000Report (Other academic)

In this paper the application of so called subspace methods for the specication and estimation of cointegrated systems is examined. This method, which is based on the state space representation, is suited for the analysis of general cointegrated systems of order one, i.e. is not limited to autoregressive models, as is e.g. Johansen's method. To assess the empirical usefulness of the method we apply it to perform a cointegration analysis of the US term structure of interest rates.

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• 233.
Vrije Universiteit Brussel, Belgium.
Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology. Vrije Universiteit Brussel, Belgium. Vrije Universiteit Brussel, Belgium. Vrije Universiteit Brussel, Belgium. Vrije Universiteit Brussel, Belgium.
A Nonlinear Multi-Proxy Model Based on Manifold Learning to Reconstruct Water Temperature from High Resolution Trace Element Profiles in Biogenic Carbonates2010In: Geoscientific Model Development, ISSN 1991-959X, E-ISSN 1991-9603, Vol. 3, no 3, p. 653-667Article in journal (Refereed)

A long standing problem in paleoceanography concerns the reconstruction of water temperature from δ18O carbonate, which for freshwater influenced environments is hindered because the isotopic composition of the ambient water (related to salinity) affects the reconstructed temperature. In this paper we argue for the use of a nonlinear multi-proxy method called Weight Determination by Manifold Regularization to develop a temperature reconstruction model that is less sensitive to salinity variations. The motivation for using this type of model is twofold: Firstly, observed nonlinear relations between specific proxies and water temperature motivate the use of nonlinear models. Secondly, the use of multi-proxy models enables salinity related variations of a given temperature proxy to be explained by salinity-related information carried by a separate proxy. Our findings confirm that Mg/Ca is a powerful paleothermometer and highlight that reconstruction performance based on this proxy is improved significantly by combining its information with the information of other trace elements in multi-proxy models. Using Mg/Ca, Sr/Ca, Ba/Ca and Pb/Ca the WDMR model enabled a temperature reconstruction with a root mean squared error of ±2.19 °C for a salinity range between 15 and 32.

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• 234.
Vrije Universiteit Brussel, Belgium.
Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology. Vrije Universiteit Brussel, Belgium. Vrije Universiteit Brussel, Belgium. Vrije Universiteit Brussel, Belgium. Vrije Universiteit Brussel, Belgium.
On Climate Reconstruction using Bivalve Shells: Three Methods to interpret the Chemical Signature of a Shell2010Report (Other academic)

The chemical composition of a bivalve shell is strongly coupled to the seasonal variations in the environment. The nonlinear nature of this relation however makes it hard to predict, e.g. the temperature, from the chemical composition of a shell. In this paper we compare the ability of three nonlinear system identification methods to reconstruct the temperature from the chemical composition of a shell. The comparison shows that nonlinear multi-proxy approaches are potential tools for climate reconstructions with a preference for manifold based methods that results in smoother and a more precise temperature reconstruction.

• 235.
Vrije Universiteit Brussel, Belgium.
Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology. Vrije Universiteit Brussel, Belgium. Vrije Universiteit Brussel, Belgium. Vrije Universiteit Brussel, Belgium. Vrije Universiteit Brussel, Belgium.
On Climate Reconstruction using Bivalve Shells: Three Methods to interpret the Chemical Signature of a Shell2009In: Proceedings of the 7th IFAC Symposium on Modelling and Control in Biomedical Systems (including Biological Systems), 2009, p. 407-412Conference paper (Refereed)

The chemical composition of a bivalve shell is strongly coupled to the seasonal variations in the environment. The nonlinear nature of this relation however makes it hard to predict, e.g. the temperature, from the chemical composition of a shell. In this paper we compare the ability of three nonlinear system identification methods to reconstruct the temperature from the chemical composition of a shell. The comparison shows that nonlinear multi-proxy approaches are potential tools for climate reconstructions with a preference for manifold based methods that results in smoother and a more precise temperature reconstruction.

• 236.
Vrije Universiteit Brussel, Belgium.
Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology. Vrije Universiteit Brussel, Belgium. Vrije Universiteit Brussel, Belgium. Vrije Universiteit Brussel, Belgium. Vrije Universiteit Brussel, Belgium.
On Climate Reconstruction Using Bivalve Shells: Three Methods To Interpret the Chemical Signature of a Shell2011In: Computer Methods and Programs in Biomedicine, ISSN 0169-2607, E-ISSN 1872-7565, Vol. 104, no 2, p. 104-111Article in journal (Refereed)

To improve our understanding of the climate process and to assess the human impact on current global warming, past climate reconstruction is essential. The chemical composition of a bivalve shell is strongly coupled to environmental variations and therefore ancient shells are potential climate archives. The nonlinear nature of the relation between environmental condition (e.g. the seawater temperature) and proxy composition makes it hard to predict the former from the latter, however. In this paper we compare the ability of three nonlinear system identification methods to reconstruct the ambient temperature from the chemical composition of a shell. The comparison shows that nonlinear multi-proxy approaches are potentially useful tools for climate reconstructions and that manifold based methods result in smoother and more precise temperature reconstruction.

• 237.
Aarhus Univ, Denmark.
Eriksholm Res Ctr, Denmark. DGS Diagnost AS, Denmark. Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, Faculty of Science & Engineering. Linköping University, The Swedish Institute for Disability Research. Eriksholm Res Ctr, Denmark. Aarhus Univ, Denmark.
Toward EEG-Assisted Hearing Aids: Objective Threshold Estimation Based on Ear-EEG in Subjects With Sensorineural Hearing Loss2018In: TRENDS IN HEARING, ISSN 2331-2165, Vol. 22, article id 2331216518816203Article in journal (Refereed)

Electrophysiological feedback on activity in the auditory pathway may potentially advance the next generation of hearing aids. Conventional electroencephalographic (EEG) systems are, however, impractical during daily life and incompatible with hearing aids. Ear-EEG is a method in which the EEG is recorded from electrodes embedded in a hearing aid like earpiece. The method therefore provides an unobtrusive way of measuring neural activity suitable for use in everyday life. This study aimed to determine whether ear-EEG could be used to estimate hearing thresholds in subjects with sensorineural hearing loss. Specifically, ear-EEG was used to determine physiological thresholds at 0.5, 1, 2, and 4 kHz using auditory steady-state response measurements. To evaluate ear-EEG in relation to current methods, thresholds were estimated from a concurrently recorded conventional scalp EEG. The threshold detection rate for ear-EEG was 20% lower than the detection rate for scalp EEG. Thresholds estimated using in-ear referenced ear-EEG were found to be elevated at an average of 5.9, 2.3, 5.6, and 1.5 dB relative to scalp thresholds at 0.5, 1, 2, and 4 kHz, respectively. No differences were found in the variance of means between in-ear ear-EEG and scalp EEG. In-ear ear-EEG, auditory steady-state response thresholds were found at 12.1 to 14.4 dB sensation level with an intersubject variation comparable to that of behavioral thresholds. Collectively, it is concluded that although further refinement of the method is needed to optimize the threshold detection rate, ear-EEG is a feasible method for hearing threshold level estimation in subjects with sensorineural hearing impairment.

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• 238.
University of Siena, Italy.
Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology. Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
Identification of Hybrid Systems via Mixed-Integer Programming2001Report (Other academic)

This paper addresses the problem of identification of hybrid dynamical systems, by focusing the attention on hinging hyperplanes (HHARX) and wiener piecewise affine (W-PWARX) autoregressive exogenous models. In particular, we provide algorithms based on mixed-integer linear or quadratic programming which are guaranteed to converge to a global optimum. We also discuss issues of state-space realization of HHARX and W-PWARX models into several existing discrete-time hybrid state-space forms.

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• 239.
Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
A Numerical Procedure for the Optimization of a Controlled Queue1980Report (Other academic)
• 240.
Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
An Approach to the Modelling and Control of Feedback Queueing Systems1984In: Proceedings of the 9th IFAC World Congress, Pergamon , 1984, p. 267-272Conference paper (Refereed)
• 241.
Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
An Approach to the Modelling and Control of Feedback Queueing Systems1983Report (Other academic)
• 242.
Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
On some Control Problems for Queues1982Doctoral thesis, monograph (Other academic)

This thesis consists of three parts. In the first one, optimal policies are constructed for some singe-line queueing situations. The second part deals with finite-state Markovian decision processes, and in the third part the practical modelling of a more complex problem is discussed and exemplified.

The central control object of part I is an M!M/1 queue with fixed arrival rate and controllable service rate. The objective is to minimize the expected long-run average of a cost rate, which isa sum of two functions, associated with the queue length (the holding cost) and the service rate (the service cost), respectively. For the case of a fin ite waiting-room, terminal costs are constructed, such that a solution to the associated dynamic programming (Bellman) equation exists, which is affine in the time parameter. The corresponding optimal control is independent of both time and the length of the control interval. It hasa form which is subsequently used in generali zing into the case of an infinite waiting room. For this case, the analysis res ults in an efficient algorithm, and in several structural results. Assuming essentially only that the holding cost is increasing, it is proved that a monotone optimal policy exists, i.e. that the optimal choice of service rate is an in creasing function of the present queue length. Three variations of the ce ntral problem are also treated in part I. These are the M/M/c problem (for which the above monotonicity result holds only under a stronger condition), the problem of a controllable ar rival rate (with fixed service rate), and the discounted cost problem.

In part II, finite-state Markovian decision processes are discussed. A brief and heuristic introduction is given, regarding continuous-time Markov chains, cost structures on these, and the problem of constructing an optimal poli cy. The purpose is to point out the relations to the queueing control problem with finite waiting-room. Counterexamples demonstrate that the approach of part I is not universally applicable.

In part 111, a simplified mode! is discussed for a situation where th e customers may reenter the queue after a stochastic delay. It is argued that under heavy-traffic conditions, the influx of reentering customers can be approximated with the output of a linear stochastic system with state-dependent Gaussian noise, whose dynamics depend on the delay distribution. This idea is exemplified with the res ults from a simulated experiment on a telephone station.

• 243.
Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
Optimal Control of Queues. Part II: The Infinite-Capacity Case1980Report (Other academic)
• 244.
Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
Optimal Control of Queues. Part I: The Finite-Capacity Case1980Report (Other academic)
• 245.
Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
Styrda köer1984Report (Other academic)
• 246.
Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
Styrda köer: En översikt över den operationsanalytiska litteraturen1980Report (Other academic)
• 247.
Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology. Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
Reglerproblem för Händelsestörda och Händelsestyrda System1982Report (Other academic)
• 248.
Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
Autonomous bucket emptying on hauler2011Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis

This thesis proposes a method of loading a hauler with an autonomous wheelloader efficiently and with high productivity in the short loading cycle. The mainidea behind the method is to raise the bucket with only the lift until the centerof gravity has reached the height that it will have just as the material will startto fall out of the bucket and on to the hauler. When the center of gravity hasreached that height both lift and tilt will be used simultaneously to keep thecenter of gravity at a constant height. This method is both faster and moreenergy efficient than loading a hauler using only one function at a time.

The method has been successfully implemented and validated by loading ahauler with three buckets with the autonomous wheel loader that is developed byVolvo CE in Eskilstuna.

Autonomous bucket emptying on hauler
• 249.
Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology. Linköping University, Department of Electrical Engineering. Linköping University, The Institute of Technology. Linköping University, The Institute of Technology.
The Development of the Applied Physics and Electrical Engineering (Y) Programme at Linköping University through Participation in the CDIO Initiative2005In: Proceedings of the 8th UICEE Annual Conference on Engineering Education, 2005, p. 321-324Conference paper (Refereed)
• 250.
Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
Pressure Control using Sensorless Voice Coil2013Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis

In this master thesis, a new method for estimating the position of the moving parts of avoice coil is presented. Instead of using a position sensor the method exploits the connectionbetween the position and the inductance of the voice coil. This is done by superpositioning a small sine voltage signal and the voice coil voltage control signal. By measuring thevoltage and current and using the fourier transform, the impedance and phase difference iscalculated which are used to compute the inductance. A medical ventilator (also known as a respirator) concept is developed with a control systemwhich takes the expiratory pressure from a higher to a lower level. The position estimationalgorithm is then used in an attempt to improve the pressure control. The result is a slightlymore stable control system. The master thesis is conducted at Maquet Critical Care (MCC) in Solna, Sweden. MCC is amedical technology company working with high performance medical ventilators. The longterm goal of this work is to develop a ventilator which is more comfortable for the patient.

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