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  • 201.
    Axehill, Daniel
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Sjöberg, Johan
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Lindqvist, Kristian
    Scania.
    Adaptive Cruise Control for Heavy Vehicles2004Inngår i: Proceedings of Reglermöte 2004, 2004Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    An Adaptive Cruise Controller (ACC) is an extension of an ordinary cruise controller. In addition to maintaining a desired set speed, an ACC can also maintain a desired time gap to the vehicle ahead. For this end, both the engine and the brakes are controlled. The interest in the MPC-controller as a solution to the problem was to achieve automatic actuator switching, thus with no explicitly defined switch points. The MPC-controller is based on a model of the system including bounds on the control signals and on linear combinations of the states. Using this knowledge, the MPC-controller will choose the correct actuator for the current driving situation. Among the drawbacks, it can be mentioned that the variant of MPC, used in this paper, is too complex to implement in the control system currently used in trucks.

  • 202.
    Axehill, Daniel
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Vandenberghe, Lieven
    University of California Los Angeles, USA.
    Hansson, Anders
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Convex Relaxations for Mixed Integer Predictive Control2010Inngår i: Automatica, ISSN 0005-1098, E-ISSN 1873-2836, Vol. 46, nr 9, s. 1540-1545Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The main objective in this work is to compare different convex relaxations for Model Predictive Control (MPC) problems with mixed real valued and binary valued control signals. In the problem description considered, the objective function is quadratic, the dynamics are linear, and the inequality constraints on states and control signals are all linear. The relaxations are related theoretically and the quality of the bounds and the computational complexities are compared in numerical experiments. The investigated relaxations include the Quadratic Programming (QP) relaxation, the standard Semidefinite Programming (SDP) relaxation, and an equality constrained SDP relaxation. The equality constrained SDP relaxation appears to be new in the context of hybrid MPC and the result presented in this work indicates that it can be useful as an alternative relaxation, which is less computationally demanding than the ordinary SDP relaxation and which often gives a better bound than the bound from the QP relaxation. Furthermore, it is discussed how the result from the SDP relaxations can be used to generate suboptimal solutions to the control problem. Moreover, it is also shown that the equality constrained SDP relaxation is equivalent to a QP in an important special case.

    Fulltekst (pdf)
    FULLTEXT01
  • 203.
    Axehill, Daniel
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Vandenberghe, Lieven
    Hansson, Anders
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    On Relaxations Applicable to Model Predictive Control for Systems with Binary Control Signals2007Rapport (Annet vitenskapelig)
    Abstract [en]

    In this work, different relaxations applicable to an MPC problem with binary control signals are compared. The relaxations considered are the QP relaxation, the standard SDP relaxation and an equality constrained SDP relaxation. The relaxations are related theoretically and both the tightness of the bounds and the computational complexities are compared in numerical experiments.The result is that the standard SDP relaxation is the one that usually gives the best bound and is most computationally demanding, while the QP relaxation is the one that gives the worst bound and is least computationally demanding. The equality constrained relaxation presented in this paper often gives a better bound than the QP relaxation and is much less computationally demanding compared to the standard SDP relaxation. Furthermore, for a special case, it is shown that the equality constrained SDP relaxation can be cast in the form of a QP. This makes it possible to replace the ordinary QP relaxation usually used in branch and bound for these problems witha tighter SDP relaxation. Numerical experiments indicate that this relaxation can decrease the overall computational time spent in branch and bound.

    Fulltekst (pdf)
    FULLTEXT01
  • 204.
    Axehill, Daniel
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Vandenberghe, Lieven
    University of California, USA.
    Hansson, Anders
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    On Relaxations Applicable to Model Predictive Control for Systems with Binary Control Signals2007Inngår i: Proceedings of the 7th IFAC Symposium on Nonlinear Control Systems, Curran Associates, Inc., 2007, s. 585-590Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this work, different relaxations applicable to an MPC problem with binary control signals are compared. The relaxations considered are the QP relaxation, the standard SDP relaxation and an alternative equality constrained SDP relaxation. The relaxations are related theoretically, and both the tightness of the bounds and the computational complexities are compared in numerical experiments. The result is that for long prediction horizons, the equality constrained SDP relaxation proposed in this paper provides a good trade-off between the quality of the relaxation and the computational time.

  • 205.
    Axell, Erik
    Linköpings universitet, Institutionen för systemteknik. Linköpings universitet, Tekniska högskolan.
    Coexistence of Real Time and Best Effort Services in Enhanced Uplink WCDMA2005Independent thesis Basic level (professional degree), 20 poäng / 30 hpOppgave
    Abstract [en]

    The increasing use of data services and the importance of IP basedservices in third generation mobile communication system (3G), requires the transmission from the cell phone to the base station, i.e. uplink, to manage high speed data rates. In the air interface for 3G in Europe, WCDMA, a concept for enhancing the transmission from the cell phone to the base station, called Enhanced Uplink, is being standardized. The overall goal is to provide high speed data access for the uplink. One of the requirements is that the enhanced uplink channels must be able to coexist with already existing WCDMA releases. For example, the enhanced uplink must not impact seriously on real time services, such as speech, carried on current WCDMA channels.

    The purpose of this work is to study how the quality, coverage and capacity of real time services carried on previous WCDMA releases is affected when introducing the Enhanced Uplink in a WCDMA network. The main focus of the study is thus to demonstrate the trade-off between voice and best effort performances.

    Theoretical assessments and simulations show that the Enhanced Uplink has many advantages over previous WCDMA releases. For example the Enhanced Uplink yields a larger system throughput for all voice loads. The noise rise, i.e. the ratio of total received power to the background noise power is being considered as the resource. It is shown that user traffic carried on the Enhanced Uplink is able to operate under a higher noise rise level as well as to get a higher throughput per noise rise. The resource is hence more efficiently utilized.

    Fulltekst (pdf)
    FULLTEXT01
  • 206.
    Axelsson, Daniel
    Linköpings universitet, Institutionen för systemteknik, Fordonssystem.
    Hastighetsstyrsystem för Förarrobot: Konstruktion, Modell, Test och Utvärdering2007Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [sv]

    De krocktester som utförs idag är låsta till det system av styr och draganordningar som byggs upp. Att göra en krocktest därbilarna kan styras individuellt med hjälp av en förarrobot ökar friheten att designa tester. Att krocka två bilar som på bilden på framsidan, med 90 graders vinkel mellan bilarnas färdriktning ställer det mest tidskritiska kravet när de ska träffa varandra. Detta kräver en bra hastighetsreglering vilket är huvuddelen i examensarbetet.

    I denna rapport redovisas hur ett sådant styrsystem skulle kunna byggas samt tester i en simuleringsmodell för denna typ av krocktest.

    Simuleringsmodellen är uppbyggd i Matlab/Simulink och eftersträvar att efterlikna ett verkligt sidokollisionstest tillräckligt mycket för att kunna testa styrsystemet.

    Efter de tester som gjorts kan man konstatera att det är möjligt att konstruera ett sådant styrsystem som kan få två bilar att träffa varandra i en sådan sidokollision som är beskriven ovan.

    Fulltekst (pdf)
    LITH-ISY-EX-4090-SE
  • 207.
    Axelsson, Erik
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik.
    Fagerstedt, Sebastian
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik.
    Robust Aircraft Positioning using Signals of Opportunity with Direction of Arrival2023Independent thesis Advanced level (degree of Master (Two Years)), 28 hpOppgave
    Abstract [en]

    This thesis considers the problem of using signals of opportunity (SOO) with known direction of arrival (DOA) for aircraft positioning. SOO is a collective name for a wide range of signals not intended for navigation but which can be intercepted by the radar warning system on an aircraft. These signals can for example aid an unassisted inertial navigation system (INS) in areas where the global navigation satellite system (GNSS) is inaccessible. Challenges arise as the signals are transmitted from non-controllable sources without any guarantee of quality and availability. Hence, it is important that any estimation method utilising SOO is robust and statistically consistent in case of time-varying signals of different quality, missed detections and unreliable signals such as outliers.

    The problem is studied using SOO sources with either known or unknown locations. An extended Kalman filter (EKF) based solution is proposed for the first case which is shown to significantly improve the localisation performance compared to an unassisted INS in common scenarios. Yet, a number of factors affect this performance, including the measurement noise variance, the signal rate and the availability of known source locations. An outlier rejection mechanism is developed which is shown to increase the robustness of the suggested method. A numerical evaluation indicates that statistical consistency can be maintained in many situations even with the above-mentioned challenges.

    An EKF based simultaneous localisation and mapping (SLAM) solution is proposed for the case with unknown SOO source locations. The flight trajectory and initialisation process of new SOO sources are critical in this case. A method based on nonlinear least squares is proposed for the initialisation process, where new SOO sources are only allowed to be initialised in the filter once a set of requirements are fulfilled. This method has shown to increase the robustness during initialisation, when the outlier rejection is not applicable. When combining known and unknown SOO source locations, a more stable localisation solution is obtained compared to when all locations are unknown. Applicability of the proposed solution is verified by a numerical evaluation.

    The computational time increases cubically with the number of sources in the state and quadratically with the number of measurements. The time is substantially increased during landmark initialisation.

    Fulltekst (pdf)
    fulltext
  • 208.
    Axelsson, Mikael
    Linköpings universitet, Institutionen för systemteknik.
    Modellbygge av mekaniksystem och riktmotorer i stridsvagn 1222002Independent thesis Basic level (professional degree)Oppgave
    Abstract [en]

    This master thesis is one part of a project, called “StabSim”, with the purpose to develop a simulation model for the align and stabilisation system in main battle tank 122. The origin of this project is that it should be possible to make control analysis without risking any hardware. Besides that it will be easy to change components in order to investigate the behaviour of the system.

    The report includes modelling of tower and weapon mechanics and also the modelling of the synchronous motors, which control these. There is also a discussion whether the model can be reduced in order to receive a less stiff system.

    To get a proper system the models needs many parameters. Some of them are unknown and that’s why this report includes methods to estimate them. Measurements have then been done on a main battle tank, and requisite parameters have been estimated.

    Fulltekst (pdf)
    FULLTEXT01
  • 209.
    Axelsson, Olle
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik.
    Controlling an autonomous underwater vehicle through tunnels with a behavior-based control strategy2011Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    The objective of the master’s thesis work is to investigate how an autonomous underwater vehicle (AUV) should act in an underwater tunnel environment. The thesis proposes sensors, control strategies, mission statement, among others, required for tunnel assignments.

    A behavior-based control (BBC) strategy has been developed to control the AUV. The BBC is used in the middle level of the vehicle control, i.e. the reactive control system which describes how the AUV navigates through a tunnel, while other events are considered. The control strategy has also been separated into two parts, and these are: controlling the AUV’s heading and controlling the AUV to a desired distance from the tunnel wall.

    To be able to evaluate the performance of the system, a graphical user interface (GUI) has been developed. The GUI enables the operator to change control settings during simulations. Two proposed control strategies are presented with simulated results.

    Fulltekst (pdf)
    Controlling an AUV through tunnels with a behavior-based control strategy
  • 210.
    Axelsson, Patrik
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    A Simulation Study on the Arm Estimation of a Joint Flexible 2 DOF Robot Arm2009Rapport (Annet vitenskapelig)
    Abstract [en]

    The main task for an industrial robot is to move the tool into specific positions. It is therefore necessary to have an accurate knowledge about the tool position. This report desrcibes a simulation study where an accelerometer attached to the robot tool is used. The acceleration and measured motor angles are used with an Extended Kalman Filter (EKF) to estimate the tool position. The work has been focused on a robot with two degrees of freedom. Simulations have been performed with different kind of errors and on different paths. The EKF uses covariance matrices of the process noise and measurement noise which are unknown. An optimization problem has therefore been proposed and solved to get covariance matrices that give good estimations.

    Fulltekst (pdf)
    A Simulation Study on the Arm Estimation of a Joint Flexible 2 DOF Robot Arm
    Fulltekst (pdf)
    FULLTEXT03
  • 211.
    Axelsson, Patrik
    Linköpings universitet, Institutionen för systemteknik.
    Automatisk trimning av en flexibel manipulator2009Independent thesis Advanced level (professional degree), 20 poäng / 30 hpOppgave
    Abstract [sv]

    Dagens industrirobotar är mycket mer komplexa än vad de var för några år sedan. Regleringen baseras på matematiska modeller och för att prestandan ska var lika bra eller bättre än förr krävs det att modellerna är anpassade till individen. Det krävs därför att modellparametrarna justeras för att stämma överens med den aktuella roboten.

    Rapporten handlar om hur de flexibla modellparametrarna ska trimmas för robotens leder så att verktygets svängningar minskar. På grund av att en rörelse på en axel påverkar de övriga axlarna, blir detta ett sexdimensionellt minimeringsproblem. Detta kan dock lösas genom att låsa vissa leder i olika positioner och på så sätt delas minimeringen upp i flera steg med som mest tre variabler att minimera över. Målfunktionen beräknas som L2-normen över den del av momentsignalen som, enligt momentframkopplingen, ska var konstant. En dåligt trimmad robot svänger mycket vilket ger ett högt målfunktionsvärde. Genom att justera de flexibla modellparametrarna kan svängningen minimeras.

    Fulltekst (pdf)
    FULLTEXT01
  • 212.
    Axelsson, Patrik
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Evaluation of Six Different Sensor Fusion Methods for an Industrial Robot using Experimental Data2012Inngår i: Proceedings of the 10th IFAC Symposium on Robot Control, 2012, s. 126-132Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Experimental evaluations for path estimation are performed on an ABB IRB4600 robot. Different observers using Bayesian techniques with different estimation models are proposed. The estimated paths are compared to the true path measured by a laser tracking system. There is no significant difference in performance between the six observers. Instead, execution time, model complexities and implementation issues have to be considered when choosing the method.

    Fulltekst (pdf)
    fulltext
  • 213.
    Axelsson, Patrik
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Evaluation of Six Different Sensor Fusion Methods for an Industrial Robot using Experimental Data2011Rapport (Annet vitenskapelig)
    Abstract [en]

    Experimental evaluations for path estimation are performed on an ABB IRB4600 robot. Different observers using Bayesian techniques with different estimation models are proposed. The estimated paths are compared to the true path measured by a laser tracking system. There is no significant difference in performance between the six observers. Instead, execution time, model complexities and implementation issues have to be considered when choosing the method.

    Fulltekst (pdf)
    fulltext
    Fulltekst (pdf)
    FULLTEXT03
  • 214.
    Axelsson, Patrik
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Grupprocessens roll i CDIO-projekten2011Rapport (Annet vitenskapelig)
    Abstract [sv]

    Den här rapporten undersöker om grupprocessen behöver behandlas mer i CDIO-projekten, än vad som är fallet idag. Rapporten undersöker också hur det ska gå till väga praktiskt. Många av de behandlade idéerna kommer från utbildningsformen problembaserat lärnade (PBL). Det visar sig att grupprocessen fungera bra trots att inte mycket tid läggs ner på att få en bra gruppdynamik, men att det naturligtvis kan bli bättre. De metoderna som finns inom PBL kan mycket väl tillämpas inom CDIO-projekten, om än något modifierade.

    Fulltekst (pdf)
    Grupprocessens roll i CDIO-projekten
    Fulltekst (pdf)
    FULLTEXT03
  • 215. Bestill onlineKjøp publikasjonen >>
    Axelsson, Patrik
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    On Sensor Fusion Applied to Industrial Manipulators2011Licentiatavhandling, monografi (Annet vitenskapelig)
    Abstract [en]

    One of the main tasks for an industrial robot is to move the end-effector in a predefined path with a specified velocity and acceleration. Different applications have different requirements of the performance. For some applications it is essential that the tracking error is extremely low, whereas other applications require a time optimal tracking. Independent of the application, the controller is a crucial part of the robot system. The most common controller configuration uses only measurements of the motor angular positions and velocities, instead of the position and velocity of the end-effector.

    The development of new cost optimised robots have introduced unwanted flexibilities in the joints and the links. It is no longer possible to get the desired performance and robustness by only measuring the motor angular positions. This thesis investigates if it is possible to estimate the end-effector position when an accelerometer is mounted at the end-effector. The main focus is to investigate Bayesian estimation methods for state estimation, here represented by the extended Kalman filter (EKF) and the particle filter (PF).

    A simulation study is performed on a two degrees of freedom industrial robot model using an EKF. The study emphasises three important problems to take care of in order to get a good performance. The first one is related to model errors which in general requires better identification methods. The second problem is about tuning of the EKF, i.e., the choice of covariance matrices for the measurement and process noise. It is desirable to have an automatic tuning procedure which minimises the estimation error and is robust to initial conditions of the tuned parameters. A variant of the expectation maximisation (EM) algorithm is proposed for estimation of the process noise covariance matrix Q. The EM algorithm iteratively estimates the unobserved state sequence and the matrix Q based on the observations of the process, where the extended Kalman smoother (EKS) is the instrument to find the unobserved state sequence.

    The third problem considers the orientation and position of the accelerometer mounted to the end-effector. A novel method to find the orientation and position of the triaxial accelerometer 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 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.

    Finally, experimental evaluations are performed on an ABB IRB4600 robot. Different observers using the EKF, EKS and PF with different estimation models are proposed. The estimated paths are compared to the true path measured by a laser tracking system. There is no significant difference in performance between the six observers. Instead, execution time, model complexities and implementation issues have to be considered when choosing the method. 

    Fulltekst (pdf)
    On Sensor Fusion Applied to Industrial Manipulators
    Download (pdf)
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  • 216. Bestill onlineKjøp publikasjonen >>
    Axelsson, Patrik
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Sensor Fusion and Control Applied to Industrial Manipulators2014Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    One of the main tasks for an industrial robot is to move the end-effector in a predefined path with a specified velocity and acceleration. Different applications have different requirements of the performance. For some applications it is essential that the tracking error is extremely small, whereas other applications require a time optimal tracking. Independent of the application, the controller is a crucial part of the robot system. The most common controller configuration uses only measurements of the motor angular positions and velocities, instead of the position and velocity of the end-effector. The development of new cost optimised robots has introduced unwanted flexibilities in the joints and the links. The consequence is that it is no longer possible to get the desired performance and robustness by only measuring the motor angular positions. 

    This thesis investigates if it is possible to estimate the end-effector position using Bayesian estimation methods for state estimation, here represented by the extended Kalman filter and the particle filter. The arm-side information is provided by an accelerometer mounted at the end-effector. The measurements consist of the motor angular positions and the acceleration of the end-effector. In a simulation study on a realistic flexible industrial robot, the angular position performance is shown to be close to the fundamental Cramér-Rao lower bound. The methods are also verified in experiments on an ABB IRB4600 robot, where the dynamic performance of the position for the end-effector is significantly improved. There is no significant difference in performance between the different methods. Instead, execution time, model complexities and implementation issues have to be considered when choosing the method. The estimation performance depends strongly on the tuning of the filters and the accuracy of the models that are used. Therefore, a method for estimating the process noise covariance matrix is proposed. Moreover, sampling methods are analysed and a low-complexity analytical solution for the continuous-time update in the Kalman filter, that does not involve oversampling, is proposed. 

    The thesis also investigates two types of control problems. First, the norm-optimal iterative learning control (ILC) algorithm for linear systems is extended to an estimation-based norm-optimal ILC algorithm where the controlled variables are not directly available as measurements. The algorithm can also be applied to non-linear systems. The objective function in the optimisation problem is modified to incorporate not only the mean value of the estimated variable, but also information about the uncertainty of the estimate. Second, H controllers are designed and analysed on a linear four-mass flexible joint model. It is shown that the control performance can be increased, without adding new measurements, compared to previous controllers. Measuring the end-effector acceleration increases the control performance even more. A non-linear model has to be used to describe the behaviour of a real flexible joint. An H-synthesis method for control of a flexible joint, with non-linear spring characteristic, is therefore proposed.

    Delarbeid
    1. Bayesian State Estimation of a Flexible Industrial Robot
    Åpne denne publikasjonen i ny fane eller vindu >>Bayesian State Estimation of a Flexible Industrial Robot
    2012 (engelsk)Inngår i: Control Engineering Practice, ISSN 0967-0661, E-ISSN 1873-6939, Vol. 20, nr 11, s. 1220-1228Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    A sensor fusion method for state estimation of a flexible industrial robot is developed. By measuring the acceleration at the end-effector, the accuracy of the arm angular position, as well as the estimated position of the end-effector are improved. The problem is formulated in a Bayesian estimation framework and two solutions are proposed; the extended Kalman filter and the particle filter. In a simulation study on a realistic flexible industrial robot, the angular position performance is shown to be close to the fundamental Cramér-Rao lower bound. The technique is also verified in experiments on an ABB robot, where the dynamic performance of the position for the end-effector is significantly improved.

    sted, utgiver, år, opplag, sider
    Elsevier, 2012
    Emneord
    Industrial robot, Positioning, Estimation, Particle filter, Extended Kalman filter, Cramér–Rao lower bound
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-81988 (URN)10.1016/j.conengprac.2012.06.004 (DOI)000309847800015 ()
    Prosjekter
    Vinnova Excellence Center LINK-SICSSF project Collaborative Localization
    Forskningsfinansiär
    VinnovaSwedish Foundation for Strategic Research
    Tilgjengelig fra: 2012-09-27 Laget: 2012-09-27 Sist oppdatert: 2021-12-06
    2. Evaluation of Six Different Sensor Fusion Methods for an Industrial Robot using Experimental Data
    Åpne denne publikasjonen i ny fane eller vindu >>Evaluation of Six Different Sensor Fusion Methods for an Industrial Robot using Experimental Data
    2012 (engelsk)Inngår i: Proceedings of the 10th IFAC Symposium on Robot Control, 2012, s. 126-132Konferansepaper, Publicerat paper (Fagfellevurdert)
    Abstract [en]

    Experimental evaluations for path estimation are performed on an ABB IRB4600 robot. Different observers using Bayesian techniques with different estimation models are proposed. The estimated paths are compared to the true path measured by a laser tracking system. There is no significant difference in performance between the six observers. Instead, execution time, model complexities and implementation issues have to be considered when choosing the method.

    Emneord
    Estimation, Extended Kalman filter, Particle filter, Accelerometer, Industrial robots
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-81456 (URN)10.3182/20120905-3-HR-2030.00003 (DOI)
    Konferanse
    10th IFAC Symposium on Robot Control, Dubrovnik, Croatia, 5-7 September 2012
    Prosjekter
    Vinnova Excellence Center LINK-SIC
    Forskningsfinansiär
    Vinnova
    Tilgjengelig fra: 2012-09-14 Laget: 2012-09-14 Sist oppdatert: 2014-04-11
    3. Discrete-time Solutions to the Continuous-time Differential Lyapunov Equation With Applications to Kalman Filtering
    Åpne denne publikasjonen i ny fane eller vindu >>Discrete-time Solutions to the Continuous-time Differential Lyapunov Equation With Applications to Kalman Filtering
    2015 (engelsk)Inngår i: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 60, nr 3, s. 632-643Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    Prediction and filtering of continuous-time stochastic processes often require a solver of a continuous-time differential Lyapunov equation (CDLE), for example the time update in the Kalman filter. Even though this can be recast into an ordinary differential equation (ODE), where standard solvers can be applied, the dominating approach in Kalman filter applications is to discretize the system and then apply the discrete-time difference Lyapunov equation (DDLE). To avoid problems with stability and poor accuracy, oversampling is often used. This contribution analyzes over-sampling strategies, and proposes a novel low-complexity analytical solution that does not involve oversampling. The results are illustrated on Kalman filtering problems in both linear and nonlinear systems.

    sted, utgiver, år, opplag, sider
    IEEE Press, 2015
    Emneord
    Continuous time systems, Discrete time systems, Kalman filters, Sampling methods
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-104790 (URN)10.1109/TAC.2014.2353112 (DOI)000350206000003 ()
    Prosjekter
    Vinnova Excellence Center LINK-SIC
    Forskningsfinansiär
    VINNOVA
    Tilgjengelig fra: 2014-02-26 Laget: 2014-02-26 Sist oppdatert: 2017-12-05
    4. ML Estimation of Process Noise Variance in Dynamic Systems
    Åpne denne publikasjonen i ny fane eller vindu >>ML Estimation of Process Noise Variance in Dynamic Systems
    2011 (engelsk)Inngår i: Proceedings of the 18th IFAC World Congress, 2011, s. 5609-5614Konferansepaper, Publicerat paper (Fagfellevurdert)
    Abstract [en]

    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.

    Emneord
    Robotic manipulators, Extended Kalman filters, Smoothing filters, Identification, Maximum likelihood, Covariance matrices
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-72219 (URN)10.3182/20110828-6-IT-1002.00543 (DOI)978-3-902661-93-7 (ISBN)
    Konferanse
    18th IFAC World Congress, Milano, Italy, 28 August-2 September, 2011
    Prosjekter
    LINK-SIC
    Tilgjengelig fra: 2011-11-28 Laget: 2011-11-23 Sist oppdatert: 2021-12-06bibliografisk kontrollert
    5. H-Controller Design Methods Applied to One Joint of a Flexible Industrial Manipulator
    Åpne denne publikasjonen i ny fane eller vindu >>H-Controller Design Methods Applied to One Joint of a Flexible Industrial Manipulator
    2014 (engelsk)Inngår i: Proceedings of the 19th IFAC World Congress, 2014 / [ed] Boje, Edward and Xia, Xiaohua, International Federation of Automatic Control , 2014, s. 210-216Konferansepaper, Publicerat paper (Fagfellevurdert)
    Abstract [en]

    Control of a flexible joint of an industrial manipulator using H design methods is presented. The considered design methods are i) mixed-H design, and ii) H loop shaping design. Two different controller configurations are examined: one uses only the actuator position, while the other uses the actuator position and the acceleration of end-effector. The four resulting controllers are compared to a standard PID controller where only the actuator position is measured. The choices of the weighting functions are discussed in details. For the loop shaping design method, the acceleration measurement is required to improve the performance compared to the PID controller. For the mixed-H method it is enough to have only the actuator position to get an improved performance. Model order reduction of the controllers is briefly discussed, which is important for implementation of the controllers in the robot control system.

    sted, utgiver, år, opplag, sider
    International Federation of Automatic Control, 2014
    Serie
    World Congress, ISSN 1474-6670 ; Volume# 19, Part# 1
    Emneord
    Robotics, Flexible, H-infinity control, Accelerometers
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-104785 (URN)10.3182/20140824-6-ZA-1003.00143 (DOI)978-3-902823-62-5 (ISBN)
    Konferanse
    19th IFAC World Congress, August 24-29, Cape Town, South Africa
    Prosjekter
    Vinnova Excellence Center LINK-SICExcellence Center at Linköping-Lund in Information Technology, ELLIIT
    Forskningsfinansiär
    VinnovaeLLIIT - The Linköping‐Lund Initiative on IT and Mobile Communications
    Tilgjengelig fra: 2014-02-26 Laget: 2014-02-26 Sist oppdatert: 2021-12-06bibliografisk kontrollert
    6. H Synthesis Method for Control of Non-linear Flexible Joint Models
    Åpne denne publikasjonen i ny fane eller vindu >>H Synthesis Method for Control of Non-linear Flexible Joint Models
    2014 (engelsk)Inngår i: Proceedings of the 19th IFAC World Congress, 2014 / [ed] Boje, Edward and Xia, Xiaohua, International Federation of Automatic Control , 2014, s. 8372-8377Konferansepaper, Publicerat paper (Fagfellevurdert)
    Abstract [en]

    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.

    sted, utgiver, år, opplag, sider
    International Federation of Automatic Control, 2014
    Serie
    World Congress, ISSN 1474-6670 ; Volume# 19, Part# 1
    Emneord
    Mechanical systems, Flexible, Robust, H-infinity Control
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-104789 (URN)10.3182/20140824-6-ZA-1003.00142 (DOI)978-3-902823-62-5 (ISBN)
    Konferanse
    19th IFAC World Congress, August 24-29, Cape Town, South Africa
    Prosjekter
    Vinnova Excellence Center LINK-SICExcellence Center at Linköping-Lund in Information Technology, ELLIIT
    Forskningsfinansiär
    VinnovaeLLIIT - The Linköping‐Lund Initiative on IT and Mobile Communications
    Tilgjengelig fra: 2014-02-26 Laget: 2014-02-26 Sist oppdatert: 2021-12-06bibliografisk kontrollert
    7. Estimation-based Norm-optimal Iterative Learning Control
    Åpne denne publikasjonen i ny fane eller vindu >>Estimation-based Norm-optimal Iterative Learning Control
    2014 (engelsk)Inngår i: Systems & control letters (Print), ISSN 0167-6911, E-ISSN 1872-7956, Vol. 73, s. 76-80Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    The norm-optimal iterative learning control (ilc) algorithm for linear systems is extended to an estimation-based norm-optimal ilc  algorithm where the controlled variables are not directly available as measurements. A separation lemma is presented, stating that if a stationary Kalman filter is used for linear time-invariant systems then the ilc  design is independent of the dynamics in the Kalman filter. Furthermore, the objective function in the optimisation problem is modified to incorporate the full probability density function of the error. Utilising the Kullback–Leibler divergence leads to an automatic and intuitive way of tuning the ilc  algorithm. Finally, the concept is extended to non-linear state space models using linearisation techniques, where it is assumed that the full state vector is estimated and used in the ilc  algorithm. Stability and convergence properties for the proposed scheme are also derived.

    sted, utgiver, år, opplag, sider
    Elsevier, 2014
    Emneord
    Iterative learning control; Estimation; Filtering; Non-linear systems
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-104791 (URN)10.1016/j.sysconle.2014.08.007 (DOI)000345108000010 ()
    Prosjekter
    Vinnova Excellence Center LINK-SICExcellence Center at Linköping-Lund in Information Technology, ELLIITSSF project Collaborative Localization
    Forskningsfinansiär
    VINNOVAeLLIIT - The Linköping‐Lund Initiative on IT and Mobile Communications
    Tilgjengelig fra: 2014-02-26 Laget: 2014-02-26 Sist oppdatert: 2021-12-06
    8. Controllability Aspects for Iterative Learning Control
    Åpne denne publikasjonen i ny fane eller vindu >>Controllability Aspects for Iterative Learning Control
    (engelsk)Manuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    This paper discusses the aspects of controllability in the iteration domain for systems that are controlled using iterative learning control (ILC). The focus is on controllability for a proposed state space model in the iteration domain and it relates to an assumption often used to prove convergence of ILC algorithms. It is shown that instead of investigating controllability it is more suitable to use the concept of target path controllability (TPC), where it is investigated if a system can follow a trajectory instead of the ability to control the system to an arbitrary point in the state space. Finally, a simulation study is performed to show how the ILC algorithm can be designed using the LQ-method, if the state space model in the iteration domain is output controllable. The LQ-method is compared to the standard norm-optimal ILC algorithm, where it is shown that the control error can be reduced significantly using the LQ-method compared to the norm-optimal approach.

    Emneord
    Iterative Learning Control, Controllability, Output controllability, Target path controllability
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-105342 (URN)
    Prosjekter
    Vinnova Excellence Center LINK-SICExcellence Center at Linköping-Lund in Information Technology, ELLIIT
    Forskningsfinansiär
    VinnovaeLLIIT - The Linköping‐Lund Initiative on IT and Mobile Communications
    Tilgjengelig fra: 2014-03-18 Laget: 2014-03-18 Sist oppdatert: 2021-12-06
    Fulltekst (pdf)
    Sensor Fusion and Control Applied to Industrial Manipulators
    Download (pdf)
    omslag
  • 217.
    Axelsson, Patrik
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Simulation Model of a 2 Degrees of Freedom Industrial Manipulator2011Rapport (Annet vitenskapelig)
    Abstract [en]

    A simulation model for a two degrees of freedom industrial manipulator where an accelerometer is attached to the robot arm is presented. An overview of the kinematic and dynamic models as well as a thorough description of the accelerometer model are given. The simulation model can be run with different types of properties, \eg model errors and disturbances. Different types of suggested simulation setups are also presented in the paper.

    Fulltekst (pdf)
    Simulation Model of a 2 Degrees of Freedom Industrial Manipulator
    Fulltekst (pdf)
    FULLTEXT03
  • 218.
    Axelsson, Patrik
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Axehill, Daniel
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Glad, Torkel
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Norrlöf, Mikael
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Controllability Aspects for Iterative Learning ControlManuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    This paper discusses the aspects of controllability in the iteration domain for systems that are controlled using iterative learning control (ILC). The focus is on controllability for a proposed state space model in the iteration domain and it relates to an assumption often used to prove convergence of ILC algorithms. It is shown that instead of investigating controllability it is more suitable to use the concept of target path controllability (TPC), where it is investigated if a system can follow a trajectory instead of the ability to control the system to an arbitrary point in the state space. Finally, a simulation study is performed to show how the ILC algorithm can be designed using the LQ-method, if the state space model in the iteration domain is output controllable. The LQ-method is compared to the standard norm-optimal ILC algorithm, where it is shown that the control error can be reduced significantly using the LQ-method compared to the norm-optimal approach.

  • 219.
    Axelsson, Patrik
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Axehill, Daniel
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Glad, Torkel
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Norrlöf, Mikael
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Iterative Learning Control - From a Controllability Point of View2014Inngår i: Proceedings of Reglermöte 2014, 2014Konferansepaper (Annet vitenskapelig)
  • 220.
    Axelsson, Patrik
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Gustafsson, Fredrik
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Discrete-time Solutions to the Continuous-time Differential Lyapunov Equation With Applications to Kalman Filtering2012Rapport (Annet vitenskapelig)
    Abstract [en]

    Prediction and filtering of continuous-time stochastic processes  require a solver of a continuous-time differential Lyapunov equation (CDLE).   Even though this can be recast into an ordinary differential equation (ODE),  where standard solvers can be applied, the dominating approach in  Kalman filter applications is to discretize the system and then  apply the discrete-time difference Lyapunov equation (DDLE). To avoid problems with  stability and poor accuracy, oversampling is often used. This  contribution analyzes over-sampling strategies, and proposes a  low-complexity analytical solution that does not involve  oversampling. The results are illustrated on Kalman filtering  problems in both linear and nonlinear systems.

    Fulltekst (pdf)
    fulltext
  • 221.
    Axelsson, Patrik
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Gustafsson, Fredrik
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Discrete-time Solutions to the Continuous-time Differential Lyapunov Equation With Applications to Kalman Filtering2015Inngår i: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 60, nr 3, s. 632-643Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Prediction and filtering of continuous-time stochastic processes often require a solver of a continuous-time differential Lyapunov equation (CDLE), for example the time update in the Kalman filter. Even though this can be recast into an ordinary differential equation (ODE), where standard solvers can be applied, the dominating approach in Kalman filter applications is to discretize the system and then apply the discrete-time difference Lyapunov equation (DDLE). To avoid problems with stability and poor accuracy, oversampling is often used. This contribution analyzes over-sampling strategies, and proposes a novel low-complexity analytical solution that does not involve oversampling. The results are illustrated on Kalman filtering problems in both linear and nonlinear systems.

    Fulltekst (pdf)
    fulltext
  • 222.
    Axelsson, Patrik
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Helmersson, Anders
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Norrlöf, Mikael
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    H-Controller Design Methods Applied to One Joint of a Flexible Industrial Manipulator2014Inngår i: Proceedings of the 19th IFAC World Congress, 2014 / [ed] Boje, Edward and Xia, Xiaohua, International Federation of Automatic Control , 2014, s. 210-216Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Control of a flexible joint of an industrial manipulator using H design methods is presented. The considered design methods are i) mixed-H design, and ii) H loop shaping design. Two different controller configurations are examined: one uses only the actuator position, while the other uses the actuator position and the acceleration of end-effector. The four resulting controllers are compared to a standard PID controller where only the actuator position is measured. The choices of the weighting functions are discussed in details. For the loop shaping design method, the acceleration measurement is required to improve the performance compared to the PID controller. For the mixed-H method it is enough to have only the actuator position to get an improved performance. Model order reduction of the controllers is briefly discussed, which is important for implementation of the controllers in the robot control system.

    Fulltekst (pdf)
    H∞-Controller Design Methods Applied to One Joint of a Flexible Industrial Manipulator
  • 223.
    Axelsson, Patrik
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Helmersson, Anders
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Norrlöf, Mikael
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    H-Controller Design Methods Applied to One Joint of a Flexible Industrial Manipulator2013Rapport (Annet vitenskapelig)
    Abstract [en]

    Control of a flexible joint of an industrial manipulator using H design methods is presented. The considered design methods are i) mixed-H design, and ii) H loop shaping design. Two different controller configurations are examined: one uses only the actuator position, while the other uses the actuator position and the acceleration of end-effector. The four resulting controllers are compared to a standard PID controller where only the actuator position is measured. The choices of the weighting functions are discussed in details. For the loop shaping design method, the acceleration measurement is required to improve the performance compared to the PID controller. For the mixed-H method it is enough to have only the actuator position to get an improved performance. Model order reduction of the controllers is briefly discussed, which is important for implementation of the controllers in the robot control system.

    Fulltekst (pdf)
    fulltext
  • 224.
    Axelsson, Patrik
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Helmersson, Anders
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Norrlöf, Mikael
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Single Joint Control of a Flexible Industrial Manipulator using H Loop Shaping2012Rapport (Annet vitenskapelig)
    Abstract [en]

    Control of a flexible joint of an industrial manipulator using H loop shaping design is presented. Two controllers are proposed; 1) H loop shaping using the actuator position, and 2) H loop shaping using the actuator position and the acceleration of end-effector. The two controllers are compared to a standard PID controller where only the actuator position is measured. Using the acceleration of the end-effector improves the nominal performance. The performance of the proposed controllers is not significantly decreased in the case of model error consisting of an increased time delay or a gain error.

    Fulltekst (pdf)
    fulltext
  • 225.
    Axelsson, Patrik
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Jung, Ylva
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Lego Segway Project Report2011Rapport (Annet vitenskapelig)
    Abstract [en]

    This project was a part of the course Applied Control and Sensor Fusion (http://www.control.isy.liu.se/student/graduate/AppliedControl/index.html) during summer and fall 2010. The goal of the course was to be a practical study of implementation issues, not always encountered in the life of a PhD student.

    A segway was constructed using a LEGO Mindstorms NXT kit and a gyro, and the goal was to construct a self balancing segway. To do this the motor angles and the gyro measurements were available, and a working Simulink program. The main focus in this project has been to construct an observer.

    The segway can be used for demos in basic control courses, and a manual can be found at the end of the report

    Fulltekst (pdf)
    Lego Segway Project Report
    Fulltekst (pdf)
    FULLTEXT03
  • 226.
    Axelsson, Patrik
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Karlsson, Rickard
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Norrlöf, Mikael
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Bayesian Methods for Estimating Tool Position of an Industrial Manipulator2012Inngår i: Proceedings of Reglermöte 2012, 2012Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    State estimation of a flexible industrial manipulator is presented using experimental data. The problem is formulated in a Bayesian framework where the extended Kalman filter and particle filter are used. The filters use the joint positions on the motor side of the gearboxes as well as the acceleration at the end-effector as measurements and estimates the corresponding joint angles on the arm side of the gearboxes. The techniques are verified on a state of the art industrial robot, and it is shown that the use of the acceleration at the end-effector improves the estimates significantly.

    Fulltekst (pdf)
    fulltext
  • 227.
    Axelsson, Patrik
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Karlsson, Rickard
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Norrlöf, Mikael
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Bayesian State Estimation of a Flexible Industrial Robot2012Inngår i: Control Engineering Practice, ISSN 0967-0661, E-ISSN 1873-6939, Vol. 20, nr 11, s. 1220-1228Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A sensor fusion method for state estimation of a flexible industrial robot is developed. By measuring the acceleration at the end-effector, the accuracy of the arm angular position, as well as the estimated position of the end-effector are improved. The problem is formulated in a Bayesian estimation framework and two solutions are proposed; the extended Kalman filter and the particle filter. In a simulation study on a realistic flexible industrial robot, the angular position performance is shown to be close to the fundamental Cramér-Rao lower bound. The technique is also verified in experiments on an ABB robot, where the dynamic performance of the position for the end-effector is significantly improved.

    Fulltekst (pdf)
    fulltext
  • 228.
    Axelsson, Patrik
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Karlsson, Rickard
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Norrlöf, Mikael
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Bayesian State Estimation of a Flexible Industrial Robot2011Rapport (Annet vitenskapelig)
    Abstract [en]

    A sensor fusion method for state estimation of a flexible industrial robot is developed. By measuring the acceleration at the end-effector, the accuracy of the arm angular position, as well as the estimated position of the end-effector are improved. The problem is formulated in a Bayesian estimation framework and two solutions are proposed; the extended Kalman filter and the particle filter. In a simulation study on a realistic flexible industrial robot, the angular position performance is shown to be close to the fundamental Cramér-Rao lower bound. The technique is also verified in experiments on an ABB robot, where the dynamic performance of the position for the end-effector is significantly improved.

    Fulltekst (pdf)
    Bayesian State Estimation of a Flexible Industrial Robot
    Fulltekst (pdf)
    FULLTEXT03
  • 229.
    Axelsson, Patrik
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Karlsson, Rickard
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Norrlöf, Mikael
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Estimation-based ILC using Particle Filter with Application to Industrial Manipulators2013Inngår i: Proceedings of the 2013 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS), 2013, s. 1740-1745Konferansepaper (Fagfellevurdert)
    Abstract [en]

    An estimation-based iterative learning control (ILC) algorithm is applied to a realistic industrial manipulator model. By measuring the acceleration of the end-effector, the arm angular position accuracy is improved when the measurements are fused with motor angle observations. The estimation problem is formulated in a Bayesian estimation framework where three solutions are proposed: one using the extended Kalman filter (EKF), one using the unscented  Kalman filter (UKF), and one using the particle filter (PF).  The estimates are used in an ILC method to improve the accuracy for following a given reference trajectory.  Since the ILC algorithm is repetitive no computational restrictions on the methods apply explicitly. In an extensive Monte Carlo simulation study it is shown that the PF method outperforms the other methods and that the ILC control law is substantially improved using the PF estimate.

    Fulltekst (pdf)
    fulltext
  • 230.
    Axelsson, Patrik
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Karlsson, Rickard
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Norrlöf, Mikael
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Estimation-based Norm-optimal Iterative Learning Control2014Inngår i: Systems & control letters (Print), ISSN 0167-6911, E-ISSN 1872-7956, Vol. 73, s. 76-80Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The norm-optimal iterative learning control (ilc) algorithm for linear systems is extended to an estimation-based norm-optimal ilc  algorithm where the controlled variables are not directly available as measurements. A separation lemma is presented, stating that if a stationary Kalman filter is used for linear time-invariant systems then the ilc  design is independent of the dynamics in the Kalman filter. Furthermore, the objective function in the optimisation problem is modified to incorporate the full probability density function of the error. Utilising the Kullback–Leibler divergence leads to an automatic and intuitive way of tuning the ilc  algorithm. Finally, the concept is extended to non-linear state space models using linearisation techniques, where it is assumed that the full state vector is estimated and used in the ilc  algorithm. Stability and convergence properties for the proposed scheme are also derived.

    Fulltekst (pdf)
    fulltext
  • 231.
    Axelsson, Patrik
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Karlsson, Rickard
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Norrlöf, Mikael
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Estimation-based Norm-optimal Iterative Learning Control2013Rapport (Annet vitenskapelig)
    Abstract [en]

    The iterative learning control (ILC) method improvesperformance of systems that repeat the same task several times. In this paper the standard norm-optimal ILC control law for linear systems is extended to an estimation-based ILC algorithm where the controlled variables are not directly available as measurements. The proposed ILC algorithm is proven to be stable and gives monotonic convergence of the error. The estimation-based part of the algorithm uses Bayesian estimation techniques such as the Kalman filter. The objective function in the optimisation problem is modified to incorporate not only the mean value of the estimated variable, but also information about the uncertainty of the estimate. It is further shown that for linear time-invariant systems the ILC design is independent of the estimation method. Finally, the concept is extended to non-linear state space models using linearisation techniques, where it is assumed that the full state vector is estimated and used in the ILC algorithm. It is also discussed how the Kullback-Leibler divergence can be used if linearisation cannot be performed. Finally, the proposed solution for non-linear systems is applied and verified in a simulation study with a simplified model of an industrial manipulator system.

    Fulltekst (pdf)
    fulltext
  • 232.
    Axelsson, Patrik
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Karlsson, Rickard
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Norrlöf, Mikael
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Tool Position Estimation of a Flexible Industrial Robot using Recursive Bayesian Methods2011Rapport (Annet vitenskapelig)
    Abstract [en]

    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.

    Fulltekst (pdf)
    Tool Position Estimation of a Flexible Industrial Robot using Recursive Bayesian Methods
    Fulltekst (pdf)
    FULLTEXT03
  • 233.
    Axelsson, Patrik
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Karlsson, Rickard
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Norrlöf, Mikael
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Tool Position Estimation of a Flexible Industrial Robot using Recursive Bayesian Methods2012Inngår i: Proceedings of the 2012 IEEE International Conference on Robotics and Automation, 2012, s. 5234-5239Konferansepaper (Fagfellevurdert)
    Abstract [en]

    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.

    Fulltekst (pdf)
    fulltext
  • 234.
    Axelsson, Patrik
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Norrlöf, Mikael
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Estimation of Orientation and Position of an Accelerometer Mounted to an Industrial Manipulator2011Rapport (Annet vitenskapelig)
    Abstract [en]

    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.

    Fulltekst (pdf)
    Estimation of Orientation and Position of an Accelerometer Mounted to an Industrial Manipulator
    Fulltekst (pdf)
    FULLTEXT03
  • 235.
    Axelsson, Patrik
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Norrlöf, Mikael
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Method to Estimate the Position and Orientation of a Triaxial Accelerometer Mounted to an Industrial Manipulator2012Inngår i: Proceedings of the 10th IFAC Symposium on Robot Control, 2012, s. 283-288Konferansepaper (Fagfellevurdert)
    Abstract [en]

    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.

    Fulltekst (pdf)
    fulltext
  • 236.
    Axelsson, Patrik
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Norrlöf, Mikael
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Method to Estimate the Position and Orientation of a Triaxial Accelerometer Mounted to an Industrial Manipulator2011Rapport (Annet vitenskapelig)
    Abstract [en]

    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.

    Fulltekst (pdf)
    Method to Estimate the Position and Orientation of a Triaxial Accelerometer Mounted to an Industrial Manipulator
    Fulltekst (pdf)
    FULLTEXT03
  • 237.
    Axelsson, Patrik
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Norrlöf, Mikael
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Wernholt, Erik
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Gustafsson, Fredrik
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Extended Kalman Filter Applied to Industrial Manipulators2010Inngår i: Proceedings of Reglermöte 2010, 2010Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    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.

    Fulltekst (pdf)
    fulltext
  • 238.
    Axelsson, Patrik
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Orguner, Umut
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Gustafsson, Fredrik
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Norrlöf, Mikael
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    ML Estimation of Process Noise Variance in Dynamic Systems2010Rapport (Annet vitenskapelig)
    Abstract [en]

    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.

    Fulltekst (pdf)
    ML Estimation of Process Noise Variance in Dynamic Systems
    Fulltekst (pdf)
    FULLTEXT05
  • 239.
    Axelsson, Patrik
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Orguner, Umut
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Gustafsson, Fredrik
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Norrlöf, Mikael
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    ML Estimation of Process Noise Variance in Dynamic Systems2011Inngår i: Proceedings of the 18th IFAC World Congress, 2011, s. 5609-5614Konferansepaper (Fagfellevurdert)
    Abstract [en]

    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.

    Fulltekst (pdf)
    fulltext
  • 240.
    Axelsson, Patrik
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Pipeleers, Goele
    Katholieke Universiteit, Leuven, Belgium.
    Helmersson, Anders
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Norrlöf, Mikael
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    H Synthesis Method for Control of Non-linear Flexible Joint Models2013Rapport (Annet vitenskapelig)
    Abstract [en]

    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.

    Fulltekst (pdf)
    fulltext
  • 241.
    Axelsson, Patrik
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Pipeleers, Goele
    Katholieke Universiteit, Leuven, Belgium.
    Helmersson, Anders
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Norrlöf, Mikael
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    H Synthesis Method for Control of Non-linear Flexible Joint Models2014Inngår i: Proceedings of the 19th IFAC World Congress, 2014 / [ed] Boje, Edward and Xia, Xiaohua, International Federation of Automatic Control , 2014, s. 8372-8377Konferansepaper (Fagfellevurdert)
    Abstract [en]

    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.

    Fulltekst (pdf)
    H∞ Synthesis Method for Control of Non-linear Flexible Joint Models
  • 242.
    Axholt, Magnus
    et al.
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Medie- och Informationsteknik. Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för teknik och naturvetenskap, Visuell informationsteknologi och applikationer.
    Skoglund, Martin
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Peterson, Stephen
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Medie- och Informationsteknik. Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för teknik och naturvetenskap, Visuell informationsteknologi och applikationer.
    Cooper, Matthew
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Medie- och Informationsteknik. Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för teknik och naturvetenskap, Visuell informationsteknologi och applikationer.
    Schön, Thomas
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Gustafsson, Fredrik
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Ynnerman, Anders
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Medie- och Informationsteknik. Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för teknik och naturvetenskap, Visuell informationsteknologi och applikationer.
    Ellis, Stephen
    NASA Ames Research Center, USA.
    Optical See-Through Head Mounted Display: Direct Linear Transformation Calibration Robustness in the Presence of User Alignment Noise2010Rapport (Annet vitenskapelig)
    Abstract [en]

    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.

    Fulltekst (pdf)
    FULLTEXT01
    Fulltekst (pdf)
    FULLTEXT03
  • 243.
    Axholt, Magnus
    et al.
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Medie- och Informationsteknik. Linköpings universitet, Tekniska högskolan.
    Skoglund, Martin
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Peterson, Stephen
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Medie- och Informationsteknik. Linköpings universitet, Tekniska högskolan.
    Cooper, Matthew
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Medie- och Informationsteknik. Linköpings universitet, Tekniska högskolan.
    Schön, Thomas
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Gustafsson, Fredrik
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Ynnerman, Anders
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Medie- och Informationsteknik. Linköpings universitet, Tekniska högskolan.
    Ellis, Stephen
    NASA Ames Research Center, USA.
    Optical See-Through Head Mounted Display: Direct Linear Transformation Calibration Robustness in the Presence of User Alignment Noise2010Inngår i: Proceedings of the 54th Annual Meeting of the Human Factors and Ergonomics Society, 2010Konferansepaper (Fagfellevurdert)
    Abstract [en]

    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.

  • 244.
    Azevedo Costa, Marcelo
    et al.
    Universidade Federal de Minas Gerais, Brazil.
    Wullt, Bernard
    Robotics and Motion Division, ABB AB.
    Norrlöf, Mikael
    Robotics and Motion Division, ABB AB.
    Gunnarsson, Svante
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska fakulteten.
    Failure detection in robotic arms using  statistical modeling, machine learning and hybrid gradient boosting2018Rapport (Annet vitenskapelig)
    Abstract [en]

    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.

    Fulltekst (pdf)
    fulltext
  • 245.
    Bachmann, Bernhard
    et al.
    Dept. Mathematics and Engineering, University of Applied Sciences, Bielefeld, Germany.
    Ochel, Lennart
    Dept. Mathematics and Engineering, University of Applied Sciences, Bielefeld, Germany.
    Ruge, Vitalij
    Dept. Mathematics and Engineering, University of Applied Sciences, Bielefeld, Germany.
    Gebremedhin, Mahder
    Linköpings universitet, Tekniska fakulteten. Linköpings universitet, Institutionen för datavetenskap, PELAB - Laboratoriet för programmeringsomgivningar.
    Fritzson, Peter
    Linköpings universitet, Tekniska fakulteten. Linköpings universitet, Institutionen för datavetenskap, PELAB - Laboratoriet för programmeringsomgivningar.
    Nezhadali, Vaheed
    Linköpings universitet, Institutionen för systemteknik, Fordonssystem. Linköpings universitet, Tekniska fakulteten.
    Eriksson, Lars
    Linköpings universitet, Institutionen för systemteknik, Fordonssystem. Linköpings universitet, Tekniska fakulteten.
    Sivertsson, Martin
    Linköpings universitet, Institutionen för systemteknik, Fordonssystem. Linköpings universitet, Tekniska fakulteten.
    Parallel Multiple-Shooting and Collocation Optimization with OpenModelica2012Inngår i: Proceedings of the 9th International MODELICA Conference; September 3-5; 2012; Munich; Germany, Linköping University Electronic Press, 2012, s. 659-668, artikkel-id 067Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Nonlinear model predictive control (NMPC) has become increasingly important for today’s control engineers during the last decade. In order to apply NMPC a nonlinear optimal control problem (NOCP) must be solved which needs a high computational effort.

    State-of-the-art solution algorithms are based on multiple shooting or collocation algorithms; which are required to solve the underlying dynamic model formulation. This paper describes a general discretization scheme applied to the dynamic model description which can be further concretized to reproduce the mul-tiple shooting or collocation approach. Furthermore; this approach can be refined to represent a total collocation method in order to solve the underlying NOCP much more efficiently. Further speedup of optimization has been achieved by parallelizing the calculation of model specific parts (e.g. constraints; Jacobians; etc.) and is presented in the coming sections.

    The corresponding discretized optimization problem has been solved by the interior optimizer Ipopt. The proposed parallelized algorithms have been tested on different applications. As industrial relevant application an optimal control of a Diesel-Electric power train has been investigated. The modeling and problem description has been done in Optimica and Modelica. The simulation has been performed using OpenModelica. Speedup curves for parallel execution are presented.

  • 246.
    Backenhof, Albert
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Medie- och Informationsteknik.
    Automatic Generation of Collision Hulls for Polygonal Objects2011Independent thesis Advanced level (professional degree), 20 poäng / 30 hpOppgave
    Abstract [en]

    Physics in interactive environments, such as computer games, and simulations require well madeand accurate bounding volumes in order to act both realistically and fast. Today it is common to useeither inaccurate boxes or spheres as bounding volumes or to model the volume by hand. Thesemethods are either too inaccurate or require too much time to ever be able to be used in real-time,accurate virtual environments.This thesis presents a method to automatically generate collision hulls for both manifolds and nonmanifolds.This allows meshes to be used in a physical environment in just a few seconds and stillbeing able to behave realistically. The method performs Approximate Convex Decomposition byiteratively dividing the mesh into smaller, more convex parts. Every part is wrapped in a convexhull. Together the hulls make an accurate, but low cost, convex representation of the original mesh.The convex hulls are stored in a bounding volume hierarchy tree structure that enables fast testingfor collision with the mesh.

    Fulltekst (pdf)
    fulltext
  • 247.
    Bakarac, Peter
    et al.
    Slovak Univ. of Tech. in Bratislava, Slovakia.
    Holaza, Juraj
    Slovak Univ. of Tech. in Bratislava, Slovakia.
    Kaluz, Martin
    Slovak Univ. of Tech. in Bratislava, Slovakia.
    Klauco, Martin
    Slovak Univ. of Tech. in Bratislava, Slovakia.
    Löfberg, Johan
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska fakulteten.
    Kvasnica, Michal
    Slovak Univ. of Tech. in Bratislava, Slovakia.
    Explicit MPC Based on Approximate Dynamic Programming2018Inngår i: 2018 EUROPEAN CONTROL CONFERENCE (ECC), 2018Konferansepaper (Fagfellevurdert)
    Abstract [en]

    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.

  • 248.
    Baral, Shawon Kumar
    Linköpings universitet, Institutionen för systemteknik, Fordonssystem.
    Closed Loop Control of PMSM Motor: Field Oriented Control Using Hall Sensors2021Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    Fossil-fuel vehicles are one of the main causes of CO2 emissions nowadays. As we are moving toward cleaner environment electrification of vehicles are becoming more and more popular. With the environment in mind, the recent improvement in battery technology and electronics has drawn a lot of attention to Brushless DC or BLDC  motors. Due to their high torque output and robust design, BLDC motors are a popular choice as the main propulsion unit in electric vehicles.  Permanent magnet synchronous motor, PMSM, is also a brushless dc motor with minor changes in design. So the word BLDC and PMSM is used interchangeably. In this thesis, two motor control algorithms were investigated. 6-Step control and Field oriented control or FOC. A three-phase inverter allows these motors to be driven by a battery. But when battery voltage goes down the speed of the motor also goes down. This thesis investigates a method to maintain the same speed at lower dc voltage. Also running of other motors than the control system was designed for. The control system performs well in simulation for two of the motor tested with the FOC algorithm. Simulation results show that the control system can track speed and current references with minimum error. Speed controller and current controllers control each parameter independently to control the motor. Low battery simulations provide useful data that shows how the field weakening technique makes it possible to achieve higher speed at low dc voltages.

    Fulltekst (pdf)
    fulltext
  • 249.
    Barbosa, Filipe Marques
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska fakulteten.
    Kullberg, Anton
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska fakulteten.
    Löfberg, Johan
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska fakulteten.
    Fast or Cheap: Time and Energy Optimal Control of Ship-to-Shore Cranes2023Inngår i: IFAC-PapersOnLine, ISSN 2405-8963, Vol. 56, nr 2, s. 3126-3131Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper addresses the trade-off between time and energy-efficiency for the problem of loading and unloading a ship. Container height constraints and energy consumption and regeneration are dealt with. We build upon a previous work that introduced a coordinate system suitable to deal with container avoidance constraints and incorporate the energy related modeling. In addition to changing the coordinate system, standard epigraph reformulations result in an optimal control problem with improved numerical properties. The trade-of is dealt with through the use of weighting of the total time and energy consumption in the cost function. An illustrative example is provided, demonstrating that the energy consumption can be substantially reduced while retaining approximately the same loading time.

  • 250.
    Barbosa, Filipe Marques
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska fakulteten.
    Löfberg, Johan
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska fakulteten.
    Time-optimal control of cranes subject to container height constraints2022Inngår i: Proceedings of 2022 American Control Conference (ACC), Institute of Electrical and Electronics Engineers (IEEE), 2022, s. 3558-3563Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    The productivity and efficiency of port operations strongly depend on how fast a ship can be unloaded and loaded again. With this in mind, ship-to-shore cranes perform the critical task of transporting containers into and onto a ship and must do so as fast as possible. Though the problem of minimizing the time spent in moving the payload has been addressed in previous studies, the different heights of the container stacks have not been the focus. In this paper, we perform a change of variable and reformulate the optimization problem to deal with the constraints on the stack heights. As consequence, these constraints become trivial and easy to represent since they turn into bound constraints when the problem is discretized for the numerical solver. To validate the idea, we simulate a small-scale scenario where different stack heights are used. The results confirm our idea and the representation of the stack constraints become indeed trivial. This approach is promising to be applied in real crane operations and has the potential to enhance their automation.

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