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  • 101.
    Mustafa, Mohammed Obaid
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system. University of Mosul, College of Engineering, Mosul, Iraq.
    Nikolakopoulos, George
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Gustafsson, Thomas
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Broken Bars Fault Diagnosis Based on Uncertainty Bounds Violation for Three Phase Induction Motors2015Ingår i: International Transactions on Electrical Energy Systems, E-ISSN 2050-7038, s. 304-325Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this article, a novel fault diagnosis scheme, based on uncertainty bounds violation, is being presented for the case of broken bars in squirrel–cage Three Phase Induction Motors. The fault diagnosis is done in two steps. Firstly the parameters of the healthy induction motor are identified using a set member- ship identification (SMI) approach, where corresponding uncertainty bounds are also being provided. Secondly the proposed uncertainty bounds violation conditions for the fault diagnosis are evaluated on–line, on the converged identified model, during a sliding time window. Multiple simulation results are presented that demonstrate the efficacy of the proposed scheme towards fault detection and diagnosis among different number of broken bars.

  • 102.
    Mustafa, Mohammed Obaid
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Nikolakopoulos, George
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Gustafsson, Thomas
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Broken rotor bar fault detection based on uncertainty ellipsoidal intersection for three phase induction motors2013Ingår i: 21st IEEE Mediterranean Conference on Control and Automation, June 25-28, Platanias, Chania, Crete, Greece, 2013., Piscataway, NJ: IEEE Communications Society, 2013, s. 388-393, artikel-id 6608751Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this article a fault detection scheme for broken rotor bar fault detection in three phase induction motor is presented. In the proposed scheme the induction motor has been transformed in the equivalent two phase (q−d) space, while the modeling of the faulty case has been also formulated. The model has been identified by the utilization of the Set Membership Identification (SMI) algorithm that has the merit of identifying both the parameters of the motor as also providing uncertainty bounds in both the healthy and the faulty cases. Based on the adopted methodology, the uncertainty bounds and the corresponding identified parameters of the induction motor is presented as 3D–ellipsoids, while a novel fast and efficient fault detection scheme has been proposed that is able to track iteratively the ellipsoid centers, the distance among centers, the intersection between the initial and a priori known converged states of the motor and the current ones, before or after the fault occurrence. Detailed analysis of the proposed approach and he fault detection strategy, as also extended simulation results are being presented that prove the efficiency of the suggested scheme.

  • 103.
    Mustafa, Mohammed Obaid
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Nikolakopoulos, George
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Gustafsson, Thomas
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Experimental evaluation of a broken rotor bar fault detection scheme based on uncertainty bounds violation2013Ingår i: 39th Annual Conference of the IEEE Industrial Electronics Society: November 10-13, 2013, Vienna, Austria, IEEE Communications Society, 2013, s. 5541-5546Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this article an experimental evaluation of a broken rotor bar fault detection scheme based on uncertainty bounds violation will be presented. The novelty of this article stems from the establishment and the experimental evaluation of fault detection scheme being able to detect faults at the beginning of its occurrence, based on Set Membership Identification and novel proposed boundary violation rules for the identified motor’s parameters. By the utilization of the SMI technique, the simplified equivalent model of the induction motor is being identified during the steady state operation (non–fault case), while at the same time safety bounds for the identified variables are being provided, based on an a priori defined corrupting additive noise. On the event of a fault, specific fault detection conditions are being proposed that can capture the fault of a broken bar. Detailed analysis of the proposed approach as also extended experimental results are being presented that prove the efficiency of the proposed scheme.

  • 104.
    Mustafa, Mohammed Obaid
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Nikolakopoulos, George
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Gustafsson, Thomas
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Fault classification scheme for three phase induction motor2014Ingår i: International Journal of System Dynamics Applications, ISSN 2160-9772, E-ISSN 2160-9799, Vol. 3, nr 1Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this article a fault classification algorithm based on a robust linear discrimination scheme, for the case of a squirrel–cage three phase induction motor, will be presented. The suggested scheme is based on a novel feature extraction mechanism from the measured magnitude and phase of current park’s vector pattern. The proposed methodology has the merit to diagnose different types of faults such as: a) broken rotor bar, and b) short circuit in stator winding. The novel feature generation technique is able to transform the problem of fault detection and diagnosis into a simpler space, where direct robust linear discrimination can be applied for solving the classification problem. Robust linear discrimination has been one of the most widely used fault detection method in real life applications, as this methodology seeks for directions that are efficient for discrimination and at the same time applies a straight forward implementation. The efficacy of the proposed scheme will be evaluated based on multiple simulation results for different fault types.

  • 105.
    Mustafa, Mohammed Obaid
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Nikolakopoulos, George
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Gustafsson, Thomas
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Fault detection based on set membership identification for three phase induction motors2012Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this article a fault detection scheme for stator winding short circuit fault detection in the case of a three phase induction motor is being presented. The three phase motor is model in (q-d) model space for the normal and the faulty case. The motor is being identified by the utilization of Set Membership Identification (SMI) that has the merit of identifying both the parameters of the motor as also providing uncertainty safety bounds by calculating orthotopes which bounds the system’s parameter vector. Based on the volume and the trend of these orthotopes, rules for identifying the existence of a fault are being presented. If the current values of the identified parameters do not lie inside the safety bounds in the healthy case, but lie in an area that is being defined by the model of the short circuit case, then a fault is being triggered.

  • 106.
    Mustafa, Mohammed Obaid
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Nikolakopoulos, George
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Gustafsson, Thomas
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Stator winding short circuit fault detection based on set membership identification for three phase induction motors2012Ingår i: 2012 20th Mediterranean Conference on Control and Automation: Barcelona, Spain, July 3-6, 2012, Piscataway, NJ: IEEE Communications Society, 2012, s. 290-296Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this article a fault detection scheme for stator winding short circuit fault detection in the case of a three phase induction motor is being presented. The three phase motor is being modeled in the equivalent two phase motor (q−d) space, while the modeling of the faulty case is being also formulated. The motor is being identified by the utilization of Set Membership Identification (SMI) that has the merit of identifying both the parameters of the motor as also providing uncertainty safety bounds by calculating orthotopes which bounds the systems parameter vector. Based on the volume and the trend of these orthotopes, rules for identifying the existence of a fault are being presented. If the current valuesof the identified parameters do not lie inside the safety bounds in the healthy case, but lie in an area that is being defined by the model of the short circuit case, then a fault is being triggered. Detailed analysis of the proposed approach as also extended simulation results are being presented that prove the efficiency of the suggested scheme.

  • 107.
    Mustafa, Mohammed Obaid
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Nikolakopoulos, George
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Gustafsson, Thomas
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Uncertainty Bounds Violation Scheme for Fault Detection in Induction Motors: Application to Broken Rotor Bars2014Konferensbidrag (Övrigt vetenskapligt)
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  • 108.
    Mustafa, Mohammed Obaid
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Nikolakopoulos, George
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Gustafsson, Thomas
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Uncertainty Bounds Violation Scheme for FaultDetection in Induction Motors: Application to Broken Rotor Bars2014Konferensbidrag (Refereegranskat)
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  • 109.
    Mustafa, Mohammed Obaid
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system. Department of Electrical Engineering, College of Eng., University of Mosul, Mosul, Iraq.
    Nikolakopoulos, George
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Gustafsson, Thomas
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Kominiak, Dariusz
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    A Fault Detection Scheme Based on Minimum Uncertainty Bounds Violation for Broken Rotor Bars in Induction Motors2016Ingår i: Control Engineering Practice, ISSN 0967-0661, E-ISSN 1873-6939, Vol. 48, s. 63-77Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this article, a novel method for broken bars fault detection in the case of three-phase induction motors and under different payloads will be presented and experimentally evaluated. In the presented approach, the cases of a partially or full broken rotor bars is being also considered, caused by: a) drilling 4mm and 8mm out of the $13$mm thickness of the same rotor bar, and b) fully drilled (13mm) one, two and three broken bars. The proposed fault detection method is based on the Set Membership Identification (SMI) technique and a novel proposed minimum boundary violation fault detection scheme, applied on the identified motor's parameters. The system identification procedure is being carried out on the simplified equivalent model of the induction motor, during the steady-state operation (non-fault case), while at the same time the proposed scheme is able to calculate on-line the corresponding safety bounds for the identified variables, based on a priori knowledge of the measuring corrupting noise (worst case encountered). The efficiency, the robustness and the overall performance of the established fault detection scheme is being extensively evaluated in multiple experimental studies and under various time instances of faults and load conditions.

  • 110.
    Mustafa, Mohammed Obaid
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Nikolakopoulos, George
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Gustafsson, Thomas
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Saied, Basil
    Department of Electrical Engineering, University of Mosul.
    Broken bar fault detection based on set membership identification for three phase induction motors2012Ingår i: Proccedings of the 9th International Conference on Informatics in Control, Automation and Robotics: Rome, Italy, 28-31, July, 2012, SciTePress, 2012, s. 224-231Konferensbidrag (Refereegranskat)
    Abstract [en]

    This article presents a fault detection scheme for the case of a broken bar occurrence in a three phase induction motor. The proposed scheme relies on Set Membership Identification (SMI) and novel proposed boundary violation rules for the identified motor’s parameters. The model of the three phase induction motor is being transformed into an equivalent two phase model, described in the q−d space, for both the normal and the faulty case. By the utilization of the SMI technique, the simplified equivalent model of the induction motor is being identified during the steady state operation (non–fault case), while at the same time safety bounds for the identified variables are being provided, based on an a priori defined corrupting additive noise. On the event of a fault, specific fault detection conditions are being proposed that can capture the specific typeof a broken bar fault. The proposed conditions depend on: a) abnormal parameter jumps, and b) rapid changes in the volume of the bounding uncertainty, which is being formulated either by ellipsoids or orthotopes. Detailed analysis of the proposed approach as also extended simulation results are being presented that prove the efficiency of the proposed scheme.

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    FULLTEXT01
  • 111.
    Mustafa, Mohammed Obaid
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Varagnolo, Damiano
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Nikolakopoulos, George
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Gustafsson, Thomas
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Detecting broken rotor bars in induction motors with model-based support vector classifiers2016Ingår i: Control Engineering Practice, ISSN 0967-0661, E-ISSN 1873-6939, Vol. 52, s. 15-23Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We propose a methodology for testing the sanity of motors when both healthy and faulty data are unavailable. More precisely, we consider a model-based Support Vector Classification (SVC) method for the detection of broken bars in three phase asynchronous motors at full load conditions, using features based on the spectral analysis of the stator's steady state current (more specifically, the amplitude of the lift sideband harmonic and the amplitude at fundamental frequency). We diverge from the mainstream focus on using SVCs trained from measured data, and instead derive a classifier that is constructed entirely using theoretical considerations. The advantage of this approach is that it does not need training steps (an expensive, time consuming and often practically infeasible task), i.e., operators are not required to have both healthy and faulty data from a system for checking it. We describe what are the theoretical properties and fundamental limitations of using model based SVC methodologies, provide conditions under which using SVC tests is statistically optimal, and present some experimental results to prove the effectiveness of the suggested scheme.

  • 112.
    Nayl, Thaker
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Nikolakopoulos, George
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Gustafsson, Thomas
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    A Full Error Dynamics Switching Modeling and Control Scheme for an Articulated Vehicle2015Ingår i: International Journal of Control, Automation and Systems, ISSN 1598-6446, E-ISSN 2005-4092, Vol. 13, nr 5, s. 1221-1232Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this article, a complete analysis towards the development of a switching modeling and control framework for an articulated vehicle, under the effect of varying slip angles will be presented. The established nonlinear kinematic model, of the nonholonomic articulated vehicle, will be transformed into an error dynamics model, which in the sequel will be linearized around multiple nominal slip angle cases. The proposed control architecture will consist of a switching control scheme, based on multiple model predictive controllers, for the articulated vehicle under varying slip angles. The controllers will be developed in order to improve the performance of the articulated vehicle's path tracking, while compensating the varying slippage effect. The current measured slip angle is being considered as the switching rule and a corresponding switching control scheme is being defined, being able to apply constraints on the states, the control signal and the output variables. Both the non-slip and slip models will be derived to highlight the significance of accounting for slips in path following control and their significant effect on deteriorating the performance of the overall control scheme when not considered. Multiple simulation results will be presented to prove the efficacy of the overall suggested scheme.

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    FULLTEXT01
  • 113.
    Nayl, Thaker
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Nikolakopoulos, George
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Gustafsson, Thomas
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Effect of Kinematic Parameters on MPC based On-line Motion Planning for an Articulated Vehicle2015Ingår i: Robotics and Autonomous Systems, ISSN 0921-8890, E-ISSN 1872-793X, Vol. 70, s. 16-24Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The aim of this article is to analyze the effect of kinematic parameters on a novel proposed on-line motion planning algorithm for an articulated vehicle based on Model Predictive Control. The kinematic parameters that are going to be investigated are the vehicle's velocity, the maximum allowable change in the articulated steering angle, the safety distance from the obstacles and the total number of obstacles in the operating arena. The proposed modified path planning algorithm for the articulated vehicle belongs to the family of Bug-Like algorithms and is able to take under consideration, the mechanical and physical constraints of the articulated vehicle, as well as its full kinematic model. During the on-line motion planning algorithm, the MPC controller controls the lateral motion of the vehicle, through the rate of the articulation angle, while driving it accurately and safely over the on-line formulated desired path. The efficiency of the proposed combined path planning and control scheme is being evaluated under numerous simulated test cases, while exhaustive simulations have been made for analyzing the dependency of the proposed framework on the kinematic parameters.

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    FULLTEXT01
  • 114.
    Nayl, Thaker
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Nikolakopoulos, George
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Gustafsson, Thomas
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Kinematic modeling and simulation studies of a LHD vehicle under slip angles2011Ingår i: The IASTED International Conference on Modelling, Simulation and Identification, Pittsburgh, USA, ACTA Press, 2011, s. 344-349Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this article a kinematic model for a Load Haul Dumping Vehicle (LHD), with the ability to take under consideration the slipping angles is being derived. This specific type of vehicles consist of two parts, a steering tractor and a trailer, linked together with rigid free joint and can be found various applications, especially in the mine fields. In the rest of the article, exhaustive simulation studies are being provided for evaluating the performance of the model under multiple design and operational variables, such as: a) multiple parameters sets for slip angles, b) different steering angles, c) various wagons’ lengths, and d) various driving paths.

  • 115.
    Nayl, Thaker
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Nikolakopoulos, George
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Gustafsson, Thomas
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Online dynamic smooth path planning for an articulated vehicle2013Ingår i: 10th International Conference on Informatics in Control, Automation and Robotics, Reykjavik, Iceland, 29-31, July, 2013, 2013, Vol. 2, s. 177-183Konferensbidrag (Refereegranskat)
    Abstract [en]

    This article proposes a novel online dynamic smooth path planning scheme based on a bug like modified path planning algorithm for an articulated vehicle under limited and sensory reconstructed surrounding static environment. In the general case collision avoidance techniques can be performed by altering the articulated steering angle to drive the front and rear parts of the articulated vehicle away from the obstacles. In the presented approach factors such as the real dynamics of the articulated vehicle, the initial and the goal configuration (displacement and orientation), minimum and total travel distance between the current and the goal points, and the geometry of the operational space are taken under consideration to calculate the update on the future way points for the articulated vehicle. In the sequel the produced path planning is being online and iteratively smoothen by the utilization of Bezier lines before producing the necessary rate of change for the vehicle’s articulated angle. The efficiency of the proposed scheme is being evaluated by multiple simulation studies.

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  • 116.
    Nayl, Thaker
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Nikolakopoulos, George
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Gustafsson, Thomas
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    On-Line Path Planning for an Articulated Vehicle based on Model Predictive Control2013Ingår i: 2013 IEEE Multi-conference on Systems and Control (Conference on Control Applications), Hyderabad, India, August 28-30, 2013, 2013, s. 772-777Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this article, a novel on–line path planning algorithm for an articulated vehicle, moving in a partially known and sensory based reconstructed environment, andrelying on Model Predictive Control will be presented. The proposed algorithm belongs to the family of bug like path planning algorithms and has the capability to take under consideration the real dynamics of the articulated vehicle.Based on: a) an a prior knowledge of the current and the goal points, and b) a partial sensory based awareness of the surrounding environment, the algorithm is able to tune online the articulated steering angle in order to drive the front and the rear parts of the vehicle from avoiding collision with obstacles, while converging to the goal point. The proposed path planning algorithm is able to produce on–line the next reference way-point, solving the local and sub-optimal problem, while in the sequel a Model Predictive Controller is being utilized forcreating the proper control signal, the rate of the articulated angle based on an error dynamics kinematic model of the vehicle. Multiple simulation results are being presented that prove the efficiency of the suggested scheme.

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  • 117.
    Nayl, Thaker
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Nikolakopoulos, George
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Gustafsson, Thomas
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Path following for an articulated vehicle based on switching model predictive control under varying speeds and slip angles2012Ingår i: 17th-ETFA 2012 - IEEE International Conference on Emerging Technology & Factory Automation,: Krakow, Poland, Sep. 17-21, 2012, Piscataway, NJ: IEEE Communications Society, 2012Konferensbidrag (Refereegranskat)
    Abstract [en]

    This article is focusing on the problem of path following for an articulated vehicle under varying velocities and slip conditions. The proposed control architecture consists of a switching control scheme based on multiple model predictive controllers, fine tuned for dealing with different operating speeds and slip angles. In the presented analysis for the non–holonomic articulated vehicle, the corresponding kinematic model is being transformed into an error dynamics model, which is linearized around multiple nominal slip angle cases and various operating speeds. The existence of the slipping and varying speed has a significant effect on the vehicle’s path following capability and can significantly deteriorate the performance of the overall control scheme. Based on the derived multiple dynamics modeling, the current slip and vehicle’s speed are being considered as the signal selector for the proposed switching model predictive control scheme. The efficacy of the proposed controller is being evaluated byan extended set of simulation results.

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  • 118.
    Nayl, Thaker
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Nikolakopoulos, George
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Gustafsson, Thomas
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Path Planning With Obstacle Avoidance and Sliding Mode Control for An Articulated Vehicle.2014Konferensbidrag (Refereegranskat)
    Abstract [en]

    A dynamic obstacle avoidance technique and control strategy to derive an articulated vehicle has been proposed. The strategy consists of two elements: a path planning and controller scheme to make the vehicle track a reference path. Potential field algorithm is exploited to generate a free collision on-line reference path in dynamic environments. The potential field is modified, by considering the nonlinear kinematic model, of the articulated vehicle. The proposed sliding mode controller is capable of making the vehicle move in minimum error displacement.

  • 119.
    Nayl, Thaker
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Nikolakopoulos, George
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Gustafsson, Thomas
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Real-Time Bug-LIke Dynamic Path Planning for an Articulated Vehicle2014Ingår i: Informatics in Control, Automation and Robotics, Switzerland: Springer International Publishing , 2014, s. 201-215Kapitel i bok, del av antologi (Refereegranskat)
    Abstract [en]

    This article proposes a novel real time bug like algorithm for performing a dynamic smooth path planning scheme for an articulated vehicle under limited and sensory reconstructed surrounding static environment. In the general case, collision avoidance techniques can be performed by altering the articulated steering angle to drive the front and rear parts of the articulated vehicle away from the obstacles. In the presented approach factors such as the real dynamics of the articulated vehicle, the initial and the goal configuration (displacement and orientation), minimum and total travel distance between the current and the goal points, and the geometry of the operational space are taken under consideration to calculate the update on the future way points for the articulated vehicle. In the sequel the produced path planning is iteratively smoothed online by the utilization of Bezier lines before producing the necessary rate of change for the vehicle’s articulated angle. The efficiency of the proposed scheme is being evaluated by multiple simulation studies that simulate the movement of the articulated vehicle in open and constrained spaces with the existence of multiple obstacles.

  • 120.
    Nayl, Thaker
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Nikolakopoulos, George
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Gustafsson, Thomas
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Switching model predictive control for an articulated vehicle2012Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this article a switching model predictive control scheme for an articulated vehicle under varying slip angles is being presented. For the non–holonomic articulated vehicle, the non–linear kinematic model that is able to take under consideration the effect of the slip angles is extracted. This model is transformed into an error dynamics model, which in the sequence is linearized around multiple nominal slip angle regions. The existence of the slip angles has a significant effect on the vehicle’s path tracking capability and can significantly deteriorate the performance of the overall control scheme. Based on the derived multiple error dynamic models, the varying slip angle is being considered as the switching rule and a corresponding switching mode predictive control scheme is being designed.

  • 121.
    Nayl, Thaker
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Nikolakopoulos, George
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Gustafsson, Thomas
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Switching model predictive control for an articulated vehicle under varying slip angle2012Ingår i: 20th IEEE Mediterranean Conference on Control and Automation: Barcelona, Spain, July 3-6, 2012, Piscataway, NJ: IEEE Communications Society, 2012, s. 884-889Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this article a switching model predictive control scheme for an articulated vehicle under varying slip angles is being presented. For the non–holonomic articulated vehicle, the non–linear kinematic model that is able to take under consideration the effect of the slip angles is extracted. This model is transformed to an error dynamics model, which in the sequence is linearized around multiple nominal slip angle cases. The existence of the slip angles has a significant effect on the vehicle’s path tracking capability and can significantly deteriorate the performance of the overall control scheme. Based on the derived multiple error dynamic models, the varying slip angle is being considered as the switching rule and a corresponding switching mode predictive control scheme is being designed that it is also able to take under consideration: a) the constrains on the control signals and b) the state constraints. Multiple simulation results are being presented that prove the efficacy of the overall suggested scheme.

  • 122.
    Nayl, Thaker
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Nikolakopoulos, George
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Gustafsson, Thomas
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Kominiak, Dariusz
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Nyberg, Rickard
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Design and experimental evaluation of a novel sliding mode controller for an articulated vehicle2018Ingår i: Robotics and Autonomous Systems, ISSN 0921-8890, E-ISSN 1872-793X, Vol. 103, s. 213-221Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This article presents the design and experimental evaluation of a novel sliding mode control scheme, being applied to the case of an articulated vehicle. The proposed sliding mode controller is based on a novel continuous sliding surface, being introduced for reducing the chattering phenomenon, while achieving a better tracking performance and a fast minimization of the corresponding tracking error. The derivation of the sliding mode controller relies on the fully nonlinear kinematic model of the articulated vehicle, while the overall stability of the control scheme is proven based on the Lyapunov's stability condition. The performance of the established control scheme is being experimentally evaluated through multiple path tracking scenarios on a small scale and fully realistic articulated vehicle

  • 123.
    Nikolakopoulos, George
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Gustafsson, Thomas
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Martinsson, Pär-Erik
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, ProcessIT Innovations R&D Centre.
    Andersson, Ulf
    Mine Tek HB, Kiruna, Sweden.
    A Vision of Zero Entry Production Areas in Mines2015Ingår i: IFAC-PapersOnLine, E-ISSN 2405-8963, Vol. 48, nr 17, s. 66-68Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This industrial article aims in presenting a short roadmap on the identified activities and technologies needed towards the vision of zero entry production areas in Mines. This work has been performed in close cooperation with large mining companies in Europe as part of the Smart Mine of the Future Research, Development and Innovation Program and will present the most important areas that it is expected the robotic technology to have an impact on.

  • 124.
    Nikolakopoulos, George
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Mustafa, Mohammed Obaid
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Gustafsson, Thomas
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Novikov, Evgeny
    Boliden, Sverige.
    Projekt: Feldetektering i elektriska maskiner2013Övrigt (Övrig (populärvetenskap, debatt, mm))
    Abstract [sv]

    Syftet med projektet är att utveckla och experimentellt utvärdera nya algoritmer för att upptäcka och isolera fel i elmotorer.

  • 125.
    Obaid, Mohammed
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Nikolakopoulos, George
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Gustafsson, Thomas
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    A survey on modeling approaches for three phase induction motors2012Ingår i: Proceedings of the IASTED International Conference on Modelling, Simulation and Identification / [ed] T. Znati; Z. Bar-Joseph; L. Rothrock, ACTA Press, 2012, s. 336-343Konferensbidrag (Refereegranskat)
    Abstract [en]

    Three–phase induction machines are generally being utilized as motors for many industrial systems, mainly due to their simple construction, low cost and other merits, when compared with other types of motors. The main aim of this article is to present a survey regarding the appeared approaches towards the mathematical modeling of three phase induction motors, which is the first step before designing appropriate control schemes. More analytically, two main modeling approaches will be presented: a) the complete three phase models, and b) the simplified quadra-ture phase models. Within these two main categories, all the types of the modeling approaches for induction motors will be presented, while the relevant significant applications, including the corresponding advantages and disadvantages for these models will be also presented. Finally, an extended bibliography is being provided as a base line for future investigations.

  • 126.
    Pauelsen, Mascha
    et al.
    Luleå tekniska universitet, Institutionen för hälsovetenskap, Hälsa, medicin och rehabilitering.
    Jafari, Hedyeh
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Strandkvist, Viktor
    Luleå tekniska universitet, Institutionen för hälsovetenskap, Hälsa, medicin och rehabilitering.
    Nyberg, Lars
    Luleå tekniska universitet, Institutionen för hälsovetenskap, Hälsa, medicin och rehabilitering.
    Gustafsson, Thomas
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Vikman, Irene
    Luleå tekniska universitet, Institutionen för hälsovetenskap, Hälsa, medicin och rehabilitering.
    Röijezon, Ulrik
    Luleå tekniska universitet, Institutionen för hälsovetenskap, Hälsa, medicin och rehabilitering.
    Frequency domain shows: Fall-related concerns and sensorimotor decline explain inability to adjust postural control strategy in older adults2020Ingår i: PLOS ONE, E-ISSN 1932-6203, Vol. 15, nr 11, artikel-id e0242608Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Human postural control is a complex system and changes as we age. Frequency based analyses have been argued to be useful to identify altered postural control strategies in balance tasks. The aim of this study was to explore the frequency domain of the quiet stance centre of pressure of older adults with various degrees of fall-related concerns and sensorimotor functioning. We included 45 community dwelling older adults and used a force plate to register 30 seconds of quiet stance with eyes open and closed respectively. We also measured sensory and motor functions, as well as fall-related concerns and morale. We analysed the centre of pressure power spectrum density and extracted the frequency of 4 of its features for each participant. Orthogonal projection of latent structures–discriminant analysis revealed two groups for each quiet stance trial. Group 1 of each trial showed less sensory and motor decline, low/no fall-related concerns and higher frequencies. Group 2 showed more decline, higher fall-related concerns and lower frequencies. During the closed eyes trial, group 1 and group 2 shifted their features to higher frequencies, but only group 1 did so in any significant way. Higher fall-related concerns, sensory and motor decline, and explorative balancing strategies are highly correlated. The control system of individuals experiencing this seems to be highly dependent on vision. Higher fall-related concerns, and sensory and motor decline are also correlated with the inability to adjust to faster, more reactive balancing strategies, when vision is not available.

  • 127. Rönnbäck, Stefan
    et al.
    Gustafsson, Thomas
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Operatörsvänliga styr- och reglerfunktioner för lasthantering med fartygskranar: Slutrapport STU-projekt 83-30391986Rapport (Övrigt vetenskapligt)
  • 128.
    Salehpour, Soheil
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Gustafsson, Thomas
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Johansson, Andreas
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    An on-line method for estimation of piecewise constant parameters in linear regression models2011Ingår i: Proceedings of the 18th IFAC World Congress: Milano, Italy, 28 August - 2 September, 2011, IFAC, International Federation of Automatic Control , 2011, s. 3171-3176Konferensbidrag (Refereegranskat)
    Abstract [en]

    We present an on-line method for detecting changes and estimating parameters in AR(X) models. The method is based on the assumption of piecewise constant parameters resulting in a sparse structure of their derivative. To illustrate the algorithm and its performance, we apply it to the change in the model parameters of some ARX models. The example illustrates that the new method shows good performance for an AR(X) model with abrupt changes in the parameters.

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  • 129.
    Salehpour, Soheil
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Johansson, Andreas
    Gustafsson, Thomas
    Fault detection of a blending tank process using mixed integer linear programming2009Ingår i: The IFAC Workshop on Automation in Mining, Mineral and Metal Industry: IFACMMM 2009, 2009Konferensbidrag (Refereegranskat)
    Abstract [en]

    The quality of iron ore pellets depends on many factors. One important issue is the mixing of binding material and slurry. It is assumed that proper mixing is achieved by keeping the material in the blender tank at an appropriate level to achieve a suitable residence time. The level of the blender is controlled by regulating the blender's hinged outflow-valve. Then, the modelling of the hinged valve is important, and the essential idea of this article is to find a method to use the process model and the available measured data to detect two detrimental conditions of the valve and warn the operators. These two conditions are: 1) The hinged valve is coated with slurry and therefore has to be cleaned to maintain its function. 2) Slurry is improperly distributed so that it does not cover the outflow valve, which then losesits authority over outflow. The valve behaviour is nonlinear and depends on the viscosity of the materials in the tank. Therefore, we use a change detection method based on Mixed Integer Linear Programming to estimate the time-varying parameters of the valve. Simulations with measurement data from the LKAB facility at Malmberget, Sweden, shows the viability of the algorithm.

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  • 130. Salehpour, Soheil
    et al.
    Johansson, Andreas
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Gustafsson, Thomas
    Parameter estimation and change detection in linear regression models using mixed integer linear programming2009Ingår i: 15th IFAC Symposium on System Identification 2009: Saint-Malo, France, 6 - 8 July 2009 / [ed] Eric Walter, Red Hook: Curran Associates, Inc., 2009Konferensbidrag (Refereegranskat)
    Abstract [en]

    We present a method for detecting changes and estimating parameters in AR(X) models. The method is based on the assumption of piecewise constant parameters resulting in a sparse structure of their derivative. To illustrate the algorithm and its performance, we apply it to the change in the mean model and compare it with four other change detection algorithms. Two applications, fuel monitoring and airbag control are treated with good results. The AR(X) change model shows good performance of the method in two illustrative examples.

  • 131. Salehpour, Soheil
    et al.
    Johansson, Andreas
    Gustafsson, Thomas
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Parameter estimation and change detection in linear regression models using mixed integer linear programming2008Ingår i: Reglermöte 2008: proceedings / [ed] Thomas Gustafsson; Wolfgang Birk; Andreas Johansson, Luleå: Luleå tekniska universitet, 2008Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    We present a method for change detection and parameter estimation in change in the mean models and AR(X) models. The method is based on the assumption of piecewise constant parameters resulting in a sparse structure of their derivative. To illustrate the algorithm and its performance, we apply it to the change in the mean model and compare it with four other change detection algorithms. Two applications, fuel monitoring and airbag control are treated with good results. The AR(X) change model, shows good performance of the method in two illustrative examples.

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  • 132.
    Salehpour, Soheil
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Johansson, Andreas
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Gustafsson, Thomas
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Regularization with hard penalty functions for on-line estimation2011Ingår i: 2011 9th IEEE International Conference on Control and Automation (ICCA 2011): Santiago, Chile, 19 - 21 December 2011, Piscataway, NJ: IEEE Communications Society, 2011, s. 195-200Konferensbidrag (Refereegranskat)
    Abstract [en]

    We present two on-line methods for detecting changes and estimating parameters in AR(X) models. The methods are based on the assumption of piecewise constant parameters resulting in a sparse structure of their derivative. Smoothly Clipped Absolute Deviation (SCAD) and hard thresholding (HT) penalty functions are two alternatives to give a sparse structure of the estimate. We use local quadratic and linear approximations of the penalty function, and the optimization is carried out by using a modified Newton-Raphson algorithm.To illustrate the algorithms and their performance, we apply them to estimate changing parameters of some ARX models. We investigate the convergence, squared error, and sparsity of the methods. The examples indicate that the local linear approximation gives better performance and is more encouraging than the local quadratic approximation.

  • 133.
    Sayyaddelshad, Saleh
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Gustafsson, Thomas
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    H observer design for uncertain nonlinear discrete-time systems with time-delay: LMI optimization approach2015Ingår i: International Journal of Robust and Nonlinear Control, ISSN 1049-8923, E-ISSN 1099-1239, Vol. 25, nr 10, s. 1514-1527Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present a robust H∞ observer for a class of nonlinear discrete-time systems. The class under study includes an unknown time-varying delay limited by upper and lower bounds, as well as time-varying para- metric uncertainties. We design a nonlinear H∞ observer, by using the upper and lower bounds of the delay, that guarantees asymptotic stability of the estimation error dynamics and is also robust against time-varying parametric uncertainties. The described problem is converted to a standard optimization problem, which can be solved in terms of linear matrix inequalities (LMIs). Then, we expand the problem to a multi-objective optimization problem in which the maximum admissible Lipschitz constant and the minimum disturbance attenuation level are the problem objectives. Finally, the proposed observer is illustrated with two examples.

  • 134.
    Sayyaddelshad, Saleh
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Gustafsson, Thomas
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Observer design for a class of nonlinear systems subject to unknown inputs2014Ingår i: 2014 European Control Conference (ECC), June 24-27, 2014. Strasbourg, France, Piscataway, NJ: IEEE Communications Society, 2014, s. 970-974, artikel-id 6862555Konferensbidrag (Refereegranskat)
    Abstract [en]

    We consider a novel method to design an observer for a class of nonlinear discrete-time systems with unknown inputs. Based on Lyapunov functional, we derive a sufficient condition for existence of the designed observer which requires solving a nonlinear matrix inequality. In light of linear algebra, the achieved condition will be formulated in terms of linear matrix inequality (LMI) that can be solved by popular methods easily. Compared to recent researches, the developed approach shows a significant better performance than other techniques previously published in literature and is less conservative in terms of Lipschitz constant. Finally, the proposed observer is illustrated by implementing the proposed method on a single- link flexible manipulator and the results are compared to some recent similar researches in terms of performance and conservativeness.

  • 135.
    Sayyaddelshad, Saleh
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Gustafsson, Thomas
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Observer Design for a Class of Nonlinear Systems Subject to Unknown Inputs2014Konferensbidrag (Refereegranskat)
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  • 136.
    Sayyaddelshad, Saleh
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Gustafsson, Thomas
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Observer Design for a Class of Nonlinear Systems Subject to Unknown Inputs2014Konferensbidrag (Övrigt vetenskapligt)
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  • 137.
    Sayyaddelshad, Saleh
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Gustafsson, Thomas
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Johansson, Andreas
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    H∞ observer design for uncertain discrete-time nonlinear delay systems: LMI optimization approach2012Ingår i: 2012 20th Mediterranean Conference on Control & Automation (MED), Piscataway, NJ: IEEE Communications Society, 2012, s. 592-597Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper, we present a robust H∞ observer for a class of nonlinear and uncertain time-delayed systems. To design the proposed observer, the time delay does not have to be exactly known. With knowledge about upper and lower bound of the delay term, we can design an H∞ observer that guarantees asymptotic stability of the estimation error dynamics and is robust against time-varying parametric uncertainties. We show that the described problem can be solved in terms of linear matrix inequalities (LMIs). In addition, the admissible Lipschitz constant of the system is maximized and the disturbance attenuation level is minimized through convex multi-objective optimization. Finally, the proposed observer is illustrated with an example.

  • 138.
    Sayyaddelshad, Saleh
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Gustafsson, Thomas
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Karimi, Hamid Reza
    Department of Engineering, Faculty of Engineering and Science, University of Agder.
    Zemouche, Ali
    Research Center for Automatic Control of Nancy, University of Lorraine.
    Observer-based control design for a class of nonlinear systems subject to unknown inputs: LMI approach2015Ingår i: 15th International Conference on Control, Automation and Systems (ICCAS): Busan, Korea (South), 13-16 Oct. 2015, Piscataway, NJ: IEEE Communications Society, 2015, s. 984-989, artikel-id 7364768Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper deals with the problem of observer-based controller design for a class of nonlinear systems subject to unknown inputs. A novel method is presented to design a controller using estimated state variables which guarantees all the state variables of the closed-loop system converge to the vicinity of the origin and stay there forever. This is done via satisfying several sufficient conditions in terms of nonlinear matrix inequalities. In light of linear algebra, particularly matrix decompositions, the achieved conditions will be converted to a Linear Matrix Inequality (LMI) problem to facilitate the procedure of computing the observer and controller gains. Finally, the effectiveness of the proposed method is illustrated by implementing on a highly nonlinear chaotic system.

  • 139.
    Sayyaddelshad, Saleh
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Johansson, Andreas
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Darouach, Mohamed
    Université de Lorraine.
    Gustafsson, Thomas
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    H∞ filter design for state estimation and unknown inputs reconstruction of a class of nonlinear systems2014Ingår i: 19th IFAC World Congress on International Federation of Automatic Control: IFAC 2014, Cape Town, South Africa 24 - 29 August 2014, 2014, s. 61-66Konferensbidrag (Refereegranskat)
    Abstract [en]

    We consider a novel method to design a H∞ filter for a class of nonlinear systems subject to unknown inputs. First, we rewrite the system dynamics as a descriptor system. Then, we design a robust H∞ reduced-order filter to estimate both state variables and unknown inputs at the same time. Based on a Lyapunov functional, we derive a sufficient condition for existence of the designed filter which requires solving a nonlinear matrix inequality. The achieved condition is further formulated in terms of a linear matrix inequality (LMI) that is straightforward to solve by popular methods. Finally, the proposed filter is illustrated with an example.

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  • 140.
    Strandkvist, Viktor
    et al.
    Luleå tekniska universitet, Institutionen för hälsovetenskap, Hälsa, medicin och rehabilitering. Department of Public Health and Clinical Medicine, The OLIN Unit, division of Occupational and Environmental Medicine, Umeå University, Robertsviksgatan 9, 971 89 Luleå, Sweden..
    Larsson, Agneta
    Luleå tekniska universitet, Institutionen för hälsovetenskap, Hälsa, medicin och rehabilitering.
    Pauelsen, Mascha
    Luleå tekniska universitet, Institutionen för hälsovetenskap, Hälsa, medicin och rehabilitering.
    Nyberg, Lars
    Luleå tekniska universitet, Institutionen för hälsovetenskap, Hälsa, medicin och rehabilitering.
    Vikman, Irene
    Luleå tekniska universitet, Institutionen för hälsovetenskap, Hälsa, medicin och rehabilitering.
    Lindberg, Anne
    Department of Public Health and Clinical Medicine, division of Medicine, Umeå University, Robertsviksgatan 9, 971 89, Luleå, Sweden.
    Gustafsson, Thomas
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Röijezon, Ulrik
    Luleå tekniska universitet, Institutionen för hälsa, lärande och teknik, Hälsa, medicin och rehabilitering.
    Hand grip strength is strongly associated with lower limb strength but only weakly with postural control in community-dwelling older adults2021Ingår i: Archives of gerontology and geriatrics (Print), ISSN 0167-4943, E-ISSN 1872-6976, Vol. 94, artikel-id 104345Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Background:

    Hand grip strength is frequently used as a measurement of muscle strength, especially among older adults. Muscle strength is only one of the many components in postural control and it is currently unclear to what extent hand grip strength is associated with postural control. The aim was to analyze the association between hand grip strength and lower limb muscle strength, and postural control among older adults.

    Methods:

    Forty-five community-dwelling individuals over 70 years of age provided isometric hand grip strength and lower limb strength (including hip extension and abduction, knee flexion and extension, and ankle dorsiflexion and plantarflexion), as well as postural control measurements. In the latter, center of pressure excursions were recorded for quiet stance and limits of stability tests on a force plate. Orthogonal projection of latent structures regression models were used to analyze associations between hand grip strength and lower limb strength as well as postural control, respectively.

    Results:

    Lower limb strength explained 74.4% of the variance in hand grip strength. All lower limb muscle groups were significantly associated with hand grip strength. In a corresponding model, postural control measured with center of pressure excursions explained 20.7% of the variance in a statistically significant, albeit weak, model.

    Conclusions:

    These results support that hand grip strength is a valid method to estimate lower limb strength among older adults on a group level. However, strength measurements seem insufficient as a substitute for measuring postural control, and therefore specific balance tests are necessary.

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