Geir Hovland

• Subedi, Dipendra; Tyapin, Ilya & Hovland, Geir (2022). Control of Redundant Flexible Manipulators with Redundancy Resolution. I IEEE, . (Red.), The 8th International Conference on Mechatronics and Robotics Engineering (ICMRE). IEEE (Institute of Electrical and Electronics Engineers). ISSN 978-1-6654-8377-3. s. 116–121. doi: 10.1109/ICMRE54455.2022.9734097. Fulltekst i vitenarkiv Vis sammendrag

  This paper deals with the online control of a redundant flexible link manipulator to achieve minimum oscillations using the redundancy resolution technique. Different redundancy resolution techniques proposed and used for rigid link manipulators are tested for their use in the case of flexible link manipulators. The simulation model of a planar three-link flexible manipulator is used in this study. The redundancy resolution using kinetic energy minimization techniques is compared with the local joint acceleration minimization method to show the advantage of achieving minimum vibrations. Keywords—Elasticity, flexibility, redundant manipulator, redundancy resolution, vibration, optimization.

• Subedi, Dipendra; Aune, Teodor N.; Tyapin, Ilya & Hovland, Geir (2022). Static Deflection Compensation of Multi-Link Flexible Manipulators Under Gravity. IEEE Access. ISSN 2169-3536. 10, s. 9658–9667. doi: 10.1109/ACCESS.2022.3144404. Fulltekst i vitenarkiv Vis sammendrag

  The static deflection compensation method of a planar multi-link flexible manipulator is proposed using the feedback from inertial sensors mounted at the tip of each link. The proposed compensation technique is validated experimentally using a high-precision laser tracker. The proposed strategy is experimentally verified using a three-link flexible manipulator. A strategy to compensate for the centripetal and tangential acceleration induced on the accelerometer mounted on the rotating link is proposed for correct inclination estimation. The improvement in the inclination estimation using the proposed compensation technique is verified both in simulation and experimental studies.

• Dybedal, Joacim & Hovland, Geir (2021). CNN-based People Detection in Voxel Space using Intensity Measurements and Point Cluster Flattening. MIC Journal: Modeling, Identification and Control. ISSN 0332-7353. 42, s. 37–46. doi: 10.4173/mic.2021.2.1.
• Subedi, Dipendra; Tyapin, Ilya & Hovland, Geir (2021). Dynamic Modeling of Planar Multi-Link Flexible Manipulators. Robotics. ISSN 2218-6581. 10(2). doi: 10.3390/robotics10020070. Fulltekst i vitenarkiv Vis sammendrag

  A closed-form dynamic model of the planar multi-link flexible manipulator is presented. The assumed modes method is used with the Lagrangian formulation to obtain the dynamic equations of motion. Explicit equations of motion are derived for a three-link case assuming two modes of vibration for each link. The eigenvalue problem associated with the mass boundary conditions, which changes with the robot configuration and payload, is discussed. The time-domain simulation results and frequency-domain analysis of the dynamic model are presented to show the validity of the theoretical derivation.

• Jha, Ajit; Subedi, Dipendra; Løvsland, Per-Ove; Tyapin, Ilya; Cenkeramaddi, Linga Reddy & Beferull-Lozano, Baltasar [Vis alle 7 forfattere av denne artikkelen] (2020). Autonomous mooring towards autonomous maritime navigation and offshore operations, 15th IEEE Conference on Industrial Electronics and Applications. Institute of Electrical and Electronics Engineers (IEEE). ISSN 978-1-7281-5168-7. s. 1171–1175. doi: 10.1109/ICIEA48937.2020.9248169.
• Aalerud, Atle & Hovland, Geir (2020). Dynamic Augmented Kalman Filtering for Human Motion Tracking under Occlusion Using Multiple 3D Sensors. IEEE Conference on Industrial Electronics and Applications. ISSN 2158-2297. s. 533–540. doi: 10.1109/ICIEA48937.2020.9248091.
• Kaldestad, Knut Berg & Hovland, Geir (2020). Laser Triangulation 3D Point Cloud Sensor with Long Range and Large Field of View. IEEE Conference on Industrial Electronics and Applications. ISSN 2158-2297. s. 561–567. doi: 10.1109/ICIEA48937.2020.9248330.
• Dybedal, Joacim & Hovland, Geir (2020). GPU-Based Optimisation of 3D Sensor Placement Considering Redundancy, Range and Field of View. IEEE Conference on Industrial Electronics and Applications. ISSN 2158-2297. s. 1484–1489. doi: 10.1109/ICIEA48937.2020.9248170.
• Dybedal, Joacim & Hovland, Geir (2020). GPU-Based Occlusion Minimisation for Optimal Placement of Multiple 3D Cameras. IEEE Conference on Industrial Electronics and Applications. ISSN 2158-2297. s. 967–972. doi: 10.1109/ICIEA48937.2020.9248399.
• Landsverk, Ronny; Zhou, Jing; Hovland, Geir & Zhang, Houxiang (2020). Modeling of Offshore Crane and Marine Craft in Wave Motion. IEEE Conference on Industrial Electronics and Applications. ISSN 2158-2297. s. 1463–1470. doi: 10.1109/ICIEA48937.2020.9248110. Fulltekst i vitenarkiv
• Aalerud, Atle & Hovland, Geir (2020). Evaluation of Perception Latencies in a Human-Robot Collaborative Environment. IEEE International Conference on Robotics and Automation (ICRA). ISSN 1050-4729. s. 5018–5023. doi: 10.1109/ICRA40945.2020.9197067.
• Subedi, Dipendra; Tyapin, Ilya & Hovland, Geir (2020). Review on Modeling and Control of Flexible Link Manipulators. MIC Journal: Modeling, Identification and Control. ISSN 0332-7353. 41(3), s. 141–163. doi: 10.4173/mic.2020.3.2. Fulltekst i vitenarkiv
• Subedi, Dipendra; Jha, Ajit; Tyapin, Ilya & Hovland, Geir (2020). Camera-LiDAR Data Fusion for Autonomous Mooring Operation. IEEE Conference on Industrial Electronics and Applications. ISSN 2158-2297. s. 1176–1181. doi: 10.1109/ICIEA48937.2020.9248089. Fulltekst i vitenarkiv
• Subedi, Dipendra; Tyapin, Ilya & Hovland, Geir (2020). Modeling and Analysis of Flexible Bodies Using Lumped Parameter Method. I Kuppuswamy, Ramesh (Red.), Proceedings of the 2020 IEEE 11th International Conference on Mechanical and Intelligent Manufacturing Technologies. IEEE (Institute of Electrical and Electronics Engineers). ISSN 9781728153322. doi: 10.1109/ICMIMT49010.2020.9041188. Vis sammendrag

  The modeling, identification and analysis of a flexible beam is presented. The lumped parameter method is used to model a flexible beam. The use of camera measurements to identify lumped parameters, namely spring stiffness and damping coefficient, is described. The measurements of the tip oscillations using a high-speed camera and high-precision laser tracker are compared. The static and dynamic behavior of the flexible beam model is compared to the experimental results to show the validity of the model.

• Hatledal, Lars Ivar; Styve, Arne; Hovland, Geir & Zhang, Houxiang (2019). A Language and Platform Independent Co-Simulation Framework Based on the Functional Mock-Up Interface. IEEE Access. ISSN 2169-3536. 7, s. 109328–109339. doi: 10.1109/ACCESS.2019.2933275. Fulltekst i vitenarkiv Vis sammendrag

  The main goal of the Functional Mock-up Interface (FMI) standard is to allow the sharing of simulation models across tools. To accomplish this, FMI relies on a combination of XML-files and compiled C-code packaged in a zip archive. This archive is called a Functional Mock-up Unit (FMU). In theory, an FMU can support multiple platforms, but not necessarily in practice. Furthermore, software libraries for interacting with FMUs may not be available in a particular language or platform. Another issue is related to the protection of intellectual property (IP). While an FMU is free to only provide the C-code in its binary form, other resources within the FMU may be unprotected. Distributing models in binary form also opens up the possibility that they may contain malicious code. In order to meet these challenges, this paper presents an open-source co-simulation framework based on FMI, which is language and platform independent thanks to the use of well-established remote procedure call (RPC) technologies. One or more FMUs are wrapped inside a server program supporting one or more language independent RPC systems over various network protocols. Together, they allow cross-platform invocation of FMUs from multiple, including previously unsupported, languages. The client-server architecture allows the effective protection of IP while also providing a means of protecting users from malicious code.

• Hatledal, Lars Ivar; Zhang, Houxiang; Styve, Arne & Hovland, Geir (2019). FMU-proxy: A Framework for Distributed Access to Functional Mock-up Units. I Haumer, Anton (Red.), Proceedings of the 13th International Modelica Conference. Linköping University Electronic Press. ISSN 978-91-7685-122-7. s. 79–86. doi: 10.3384/ecp1915779. Fulltekst i vitenarkiv Vis sammendrag

  The main goal of the Functional Mock-up Interface (FMI) standard is to allow simulation models to be shared across tools. To accomplish this, FMI relies on a combination of XML-files and compiled C-code packaged in a zip archive. This archive is called an Functional Mock-up Unit (FMU) and uses the extension .fmu. In theory, an FMU can support multiple platforms, however this is not always the case and depends on the type of binaries the exporting tool was able to provide. Furthermore, a library providing FMI support may not be available in a particular language, and/or it may not support the whole standard. Another issue is related to the protection of Intellectual Property (IP). While an FMU is free to only provide the C-code in binary form, other resources shipped with the FMU may be unprotected. In order to overcome these challenges, this paper presents FMU-proxy, an open-source framework for accessing FMUs across languages and platforms. This is done by wrapping one or more FMUs behind a server program supporting multiple language independent Remote Procedure Call (RPC) technologies over several network protocols. Currently, Apache Thrift (TCP/IP, HTTP), gRPC (HTTP/2) and JSON-RPC (HTTP, WebSockets, TPC/IP, ZeroMQ) are supported. Together, they allow FMUs to be invoked from virtually any language on any platform. As users don’t have direct access to the FMU or the resources within it, IP is more effectively protected.

• Røsjordet, Jan Fredrik & Hovland, Geir (2019). Methods for experimentally determining stiffness of a multi-axis machining centre. MIC Journal: Modeling, Identification and Control. ISSN 0332-7353. 40(1), s. 11–25. doi: 10.4173/mic.2019.1.2. Fulltekst i vitenarkiv
• Aalerud, Atle; Dybedal, Joacim & Hovland, Geir (2019). Automatic Calibration of an Industrial RGB-D Camera Network Using Retroreflective Fiducial Markers. Sensors. ISSN 1424-8220. 19(7). doi: 10.3390/s19071561. Fulltekst i vitenarkiv Vis sammendrag

  This paper describes a non-invasive, automatic, and robust method for calibrating a scalable RGB-D sensor network based on retroreflective ArUco markers and the iterative closest point (ICP) scheme. We demonstrate the system by calibrating a sensor network comprised of six sensor nodes positioned in a relatively large industrial robot cell with an approximate size of 10 m × 10 m × 4 m. Here, the automatic calibration achieved an average Euclidean error of 3 cm at distances up to 9.45 m. To achieve robustness, we apply several innovative techniques: Firstly, we mitigate the ambiguity problem that occurs when detecting a marker at long range or low resolution by comparing the camera projection with depth data. Secondly, we use retroreflective fiducial markers in the RGB-D calibration for improved accuracy and detectability. Finally, the repeating ICP refinement uses an exact region of interest such that we employ the precise depth measurements of the retroreflective surfaces only. The complete calibration software and a recorded dataset are publically available and open source.

• Dybedal, Joacim; Aalerud, Atle & Hovland, Geir (2019). Embedded Processing and Compression of 3D Sensor Data for Large Scale Industrial Environments. Sensors. ISSN 1424-8220. 19(3). doi: 10.3390/s19030636. Fulltekst i vitenarkiv Vis sammendrag

  This paper presents a scalable embedded solution for processing and transferring 3D point cloud data. Sensors based on the time-of-flight principle generate data which are processed on a local embedded computer and compressed using an octree-based scheme. The compressed data is transferred to a central node where the individual point clouds from several nodes are decompressed and filtered based on a novel method for generating intensity values for sensors which do not natively produce such a value. The paper presents experimental results from a relatively large industrial robot cell with an approximate size of 10 m × 10 m × 4 m. The main advantage of processing point cloud data locally on the nodes is scalability. The proposed solution could, with a dedicated Gigabit Ethernet local network, be scaled up to approximately 440 sensor nodes, only limited by the processing power of the central node that is receiving the compressed data from the local nodes. A compression ratio of 40.5 was obtained when compressing a point cloud stream from a single Microsoft Kinect V2 sensor using an octree resolution of 4 cm.

• Tørdal, Sondre Sanden & Hovland, Geir (2019). Ship-to-Ship State Observer using Sensor Fusion and the Extended Kalman Filter. Journal of Offshore Mechanics and Arctic Engineering. ISSN 0892-7219. 141(4). doi: 10.1115/1.4041643. Vis sammendrag

  In this paper, a solution for estimating the relative position and orientation between two ships in six degrees-of-freedom (6DOF) using sensor fusion and an extended Kalman filter (EKF) approach is presented. Two different sensor types, based on time-of-flight and inertial measurement principles, were combined to create a reliable and redundant estimate of the relative motion between the ships. An accurate and reliable relative motion estimate is expected to be a key enabler for future ship-to-ship operations, such as autonomous load transfer and handling. The proposed sensor fusion algorithm was tested with real sensors (two motion reference units (MRS) and a laser tracker) and an experimental setup consisting of two Stewart platforms in the Norwegian Motion Laboratory, which represents an approximate scale of 1:10 when compared to real-life ship-to-ship operations.

• Tyapin, Ilya & Hovland, Geir (2018). Long Arm Manipulator Path Interpolation Using 4th Order B-Splines. I -, IEEE (Red.), International Conference on Control, Automation and Systems (ICCAS), 18th. IEEE conference proceedings. ISSN 978-89-93215-16-8.
• Tørdal, Sondre Sanden; Hovland, Geir & Olsen, Jan Thomas (2018). The Norwegian Motion-Laboratory. MIC Journal: Modeling, Identification and Control. ISSN 0332-7353. 39(3), s. 191–208. doi: 10.4173/mic.2018.3.5. Vis sammendrag

  This paper contains an overview of the equipment currently available in the Norwegian Motion Laboratory,a description of the IT networking infrastructure in the laboratory, a GitHub link to open source codedeveloped, description of the PyQt-based graphical user interface, presentation of robot forward andinverse kinematics, presentation of equations of motion for the suspended load motion and a descriptionof the full system kinematics. The paper ends with a list of research experiments and publications fromthe laboratory to date.

• Hatledal, Lars Ivar; Zhang, Houxiang; Styve, Arne & Hovland, Geir (2018). FMI4j: A Software Package for working with Functional Mock-up Units on the Java Virtual Machine. I Øi, Lars Erik; Komulainen, Tiina M.; Bye, Robin Trulssen & Nord, Lars O. (Red.), Proceedings of The 59th Conference on Simulation and Modelling (SIMS 59). Linköping University Electronic Press. ISSN 978-91-7685-494-5. s. 37–42. doi: 10.3384/ecp1815337. Fulltekst i vitenarkiv
• Kucera, Jan & Hovland, Geir (2018). Tail removal block validation: Implementation and analysis. MIC Journal: Modeling, Identification and Control. ISSN 0332-7353. 39(3), s. 151–156. doi: 10.4173/mic.2018.3.1.
• Gøytil, Petter Hansen; Hansen, Michael Rygaard & Hovland, Geir (2018). Iterative learning applied to hydraulic pressure control. MIC Journal: Modeling, Identification and Control. ISSN 0332-7353. 39(1), s. 1–14. doi: 10.4173/mic.2018.1.1.
• Brunete, Alberto; Gambao, Ernesto; Koskinen, Jukka; Heikkila, Tapio; Kaldestad, Knut Berg & Tyapin, Ilya [Vis alle 11 forfattere av denne artikkelen] (2018). Hard material small-batch industrial machining robot. Robotics and Computer-Integrated Manufacturing. ISSN 0736-5845. 54, s. 185–199. doi: 10.1016/j.rcim.2017.11.004. Fulltekst i vitenarkiv
• Aalerud, Atle; Dybedal, Joacim; Ujkani, Erind & Hovland, Geir (2018). Industrial Environment Mapping Using Distributed Static 3D Sensor Nodes, 2018 14th IEEE/ASME International Conference on Mechatronic and Embedded Systems and Applications (MESA). IEEE conference proceedings. ISSN 978-1-5386-4643-4. doi: 10.1109/MESA.2018.8449203. Vis sammendrag

  This paper presents a system architecture for mapping and real-time monitoring of a relatively large industrial robotic environment of size 10 m × 15 m × 5 m. Six sensor nodes with embedded computing power and local processing of the 3D point clouds are placed close to the ceiling. The system architecture and data processing is based on the Robot Operating System (ROS) and the Point Cloud Library (PCL). The 3D sensors used are the Microsoft Kinect for Xbox One and point cloud data is collected at 20 Hz. A new manual calibration procedure is developed using reflective planes. The specified range of the used sensor is 0.8 m to 4.2 m, while depth data up to 9 m is used in this paper. Despite the fact that only six sensors are used and that the Kinect sensors are operated beyond the specified range, a benchmark of the accuracy compared with a Leica laser distance meter demonstrates an accuracy of 10 mm or better in the final 3D point cloud.

• Aalerud, Atle; Dybedal, Joacim & Hovland, Geir (2018). Scalability of GPU-Processed 3D Distance Maps for Industrial Environments, 2018 14th IEEE/ASME International Conference on Mechatronic and Embedded Systems and Applications (MESA). IEEE conference proceedings. ISSN 978-1-5386-4643-4. doi: 10.1109/MESA.2018.8449160.
• Ujkani, Erind; Dybedal, Joacim; Aalerud, Atle; Kaldestad, Knut Berg & Hovland, Geir (2018). Visual Marker Guided Point Cloud Registration in a Large Multi-Sensor Industrial Robot Cell, 2018 14th IEEE/ASME International Conference on Mechatronic and Embedded Systems and Applications (MESA). IEEE conference proceedings. ISSN 978-1-5386-4643-4. doi: 10.1109/MESA.2018.8449195.
• Hovland, Geir & Kucera, Jan (2017). Nonlinear Feedback Control and Stability Analysis of a Proof-of-Work Blockchain. MIC Journal: Modeling, Identification and Control. ISSN 0332-7353. doi: 10.4173/mic.2017.4.1.
• Tørdal, Sondre Sanden & Hovland, Geir (2017). Inverse kinematic control of an industrial robot used in Vessel-to-Vessel Motion Compensation. I Koutsoukos, Xenofon & Bugeja, Marvin (Red.), 25th Mediterranean Conference on Control and Automation. IEEE conference proceedings. ISSN 978-1-5090-4533-4. doi: 10.1109/MED.2017.7984313.
• Tørdal, Sondre Sanden; Pawlus, Witold & Hovland, Geir (2017). Real-time 6-DOF Vessel-to-Vessel Motion Compensation using laser tracker, IEEE OCEANS 2017 - Aberdeen. IEEE conference proceedings. ISSN 978-1-5090-5278-3. doi: 10.1109/OCEANSE.2017.8084756.
• Ujkani, Erind; Eppeland, Petter Sait; Aalerud, Atle & Hovland, Geir (2017). Real-time human collision detection for industrial robot cells. I Hanebeck, Uwe D. (Red.), 2017 IEEE International Conference on Multisensor Fusion and Integration for Intelligent Systems (MFI). IEEE conference proceedings. ISSN 978-1-5090-6064-1. s. 488–493. doi: 10.1109/MFI.2017.8170368.
• Tørdal, Sondre Sanden & Hovland, Geir (2017). Relative vessel motion tracking using sensor fusion, Aruco markers, and MRU sensors. MIC Journal: Modeling, Identification and Control. ISSN 0332-7353. 38(2), s. 79–93. doi: 10.4173/mic.2017.2.3.
• Dybedal, Joacim & Hovland, Geir (2017). Optimal placement of 3D sensors considering range and field of view, Proceedings: IEEE International Conference on Advanced Intelligent Mechatronics (AIM 2017). IEEE (Institute of Electrical and Electronics Engineers). ISSN 9781509020669. s. 1588–1593. doi: 10.1109/AIM.2017.8014245. Vis sammendrag

  This paper describes a novel approach to the problem of optimal placement of 3D sensors in a specified volume of interest. The coverage area of the sensors is modelled as a cone having limited field of view and range. The volume of interest is divided into many, smaller cubes each having a set of associated Boolean and continuous variables. The proposed method could be easily extended to handle the case where certain sub-volumes must be covered by several sensors (redundancy), for example ex-zones, regions where humans are not allowed to enter or regions where machine movement may obstruct the view of a single sensor. The optimisation problem is formulated as a Mixed-Integer Linear Program (MILP) utilising logical constraints and piecewise linearisation of nonlinear functions. The final MILP problem is solved using the Cplex solver interfaced with Matlab.

• Pawlus, Witold; Liland, Fred; Nilsen, Nicolai; Øydna, Søren; Hovland, Geir & Wroldsen, Torstein Kurt (2017). Modeling and simulation of a cylinder hoisting system for real-time hardware-in-the-loop testing. SPE Drilling & Completion. ISSN 1064-6671. 32(1), s. 69–78. doi: 10.2118/184406-PA.
• Tørdal, Sondre Sanden; Hovland, Geir Edvin & Tyapin, Ilya (2017). Efficient Implementation of Inverse Kinematics on a 6-DOF Industrial Robot using Conformal Geometric Algebra. Advances in Applied Clifford Algebras. ISSN 0188-7009. 27(3), s. 2067–2082. doi: 10.1007/s00006-016-0698-2. Vis sammendrag

  This paper presents an implementation of the inverse kinematics (IK) solution for an industrial robot based on Conformal Geometric Algebra where the correct signs of the joint angles are extracted using the multivector coefficients and applying the forward kinematics. The solution presented is twice as fast as traditional IK algorithms implemented using matrix algebra, and more than 45 times faster than the IK provided by the robot manufacturer. The proposed solution has been successfully demonstrated and benchmarked in a 3-DOF motion compensation experiment. In addition to being efficient the presented solution requires less matrix operations than for the traditional IK.

• Pawlus, Witold; Hansen, Michael Rygaard; Choux, Martin Marie Hubert & Hovland, Geir (2016). Mitigation of Fatigue Damage and Vibration Severity of Electric Drivetrains by Systematic Selection of Motion Profiles. IEEE/ASME transactions on mechatronics. ISSN 1083-4435. 21(6), s. 2870–2880. doi: 10.1109/TMECH.2016.2573587.
• Pawlus, Witold; Choux, Martin Marie Hubert; Hansen, Michael Rygaard & Hovland, Geir (2016). Load torque estimation method to design electric drivetrains for offshore pipe handling equipment. Journal of Offshore Mechanics and Arctic Engineering. ISSN 0892-7219. 138(4). doi: 10.1115/1.4032897.
• Pawlus, Witold; Ebbesen, Morten Kjeld; Hansen, Michael Rygaard; Choux, Martin Marie Hubert & Hovland, Geir (2016). Comparative analysis of numerical models of pipe handling equipment used in offshore drilling applications. AIP Conference Proceedings. ISSN 0094-243X. 1738. doi: 10.1063/1.4952158.
• Tørdal, Sondre Sanden; Løvsland, Per-Ove & Hovland, Geir (2016). Testing of Wireless Sensor Performance in Vessel-to-Vessel Motion Compensation, 42nd Annual Conference of the IEEE Industrial Electronics Society (IECON2016). IEEE conference proceedings. ISSN 978-1-5090-3474-1. s. 654–659. doi: 0.1109/IECON.2016.7793951.
• Kaldestad, Knut Berg; Tyapin, Ilya & Hovland, Geir (2015). Robotic face milling path correction and vibration reduction, 2015 IEEE International Conference on Advanced Intelligent Mechatronics (AIM 2015). Curran Associates, Inc.. ISSN 9781467391085. s. 543–548. doi: 10.1109/AIM.2015.7222591.
• Tyapin, Ilya; Kaldestad, Knut Berg & Hovland, Geir (2015). Off-line path correction of robotic face milling using static tool force and robot stiffness, 2015 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS 2015). Curran Associates, Inc.. ISSN 9781479999958. s. 5506–5511. doi: 10.1109/IROS.2015.7354157.
• Pawlus, Witold; Hansen, Michael Rygaard; Hovland, Geir & Choux, Martin Marie Hubert (2015). Torque Peak Reduction and Overload Monitoring of Induction Motors in Offshore Drilling Operations, ACEMP 2015 Optim - Electromotion Joint Conference. IEEE Press. ISSN 978-1-4673-7240-4. s. 393–398. doi: 10.1109/OPTIM.2015.7426962.
• Pawlus, Witold; Frick, Damian; Morari, Manfred; Hovland, Geir & Choux, Martin Marie Hubert (2015). Drivetrain Design Optimization for Electrically Actuated Systems via Mixed Integer Programing, Proceedings IECON 2015 - 41st Annual Conference of the IEEE Industrial Electronics Society. IEEE conference proceedings. ISSN 978-1-4799-1761-7. s. 1465–1470. doi: 10.1109/IECON.2015.7392307.
• Magnussen, Øyvind; Ottestad, Morten & Hovland, Geir Edvin (2015). Multicopter design optimization and validation. MIC Journal: Modeling, Identification and Control. ISSN 0332-7353. 36(2), s. 67–79. doi: 10.4173/mic.2015.2.1.
• Pawlus, Witold; Liland, Fred; Nilsen, Nicolai; Søren, Øydna; Hovland, Geir & Wroldsen, Torstein Kurt (2014). Optimization of a High Fidelity Virtual Model of a Hydraulic Hoisting System for Real-Time Simulations, International Petroleum Technology Conference, 10-12 December, Kuala Lumpur, Malaysia. International Petroleum Technology Conference. ISSN 978-1-61399-371-2. s. 1–11. doi: 10.2523/iptc-17780-ms.
• Pawlus, Witold; Choux, Martin Marie Hubert; Hovland, Geir; Hansen, Michael Rygaard & Søren, Øydna (2014). Modeling and Simulation of An Offshore Pipe Handling Machine. I Rezania Kolaei, Alireza (Red.), The 55th Conference on Simulation and Modelling (SIMS 55) Proceedings. Linköping Electronic Conference Proceedings. ISSN 9789175193762. s. 277–284. doi: 10.1063/1.4952158.
• Tyapin, Ilya; Hovland, Geir & Brogårdh, Torgny (2014). Method for Estimating Combined Controller, Joint and Link Stiffnesses of an Industrial Robot. I NN, NN (Red.), 2014 IEEE International Symposium on Robotic and Sensors Environments (ROSE). Curran Associates, Inc.. ISSN 9781479949250. doi: 10.1109/ROSE.2014.6952974.
• Magnussen, Øyvind; Hovland, Geir; Ottestad, Morten & Kirby, Simon (2014). Experimental Study on the Influence of Controller Firmware on Multirotor Actuator Dynamics. I NN, NN (Red.), 2014 IEEE International Symposium on Robotic and Sensors Environments (ROSE). Curran Associates, Inc.. ISSN 9781479949250. doi: 10.1109/ROSE.2014.6952992.
• Kaldestad, Knut Berg; Haddadin, Sami; Belder, Rico; Hovland, Geir & Anisi, Alireza David (2014). Collision Avoidance with Potential Fields Based on Parallel Processing of 3D-Point Cloud Data on the GPU, 2014 IEEE International Conference on Robotics and Automation (ICRA 2014). Curran Associates, Inc.. ISSN 9781479936861. s. 3250–3257. doi: 10.1109/icra.2014.6907326.
• Magnussen, Øyvind; Hovland, Geir & Ottestad, Morten (2014). Multicopter UAV Design Optimization, 2014 IEEE/ASME 10th International Conference on Mechatronic and Embedded Systems and Applications(MESA). IEEE (Institute of Electrical and Electronics Engineers). ISSN 9781479922802. doi: 10.1109/MESA.2014.6935598.
• Tyapin, Ilya; Hovland, Geir; Kosonen, Petri & Linna, Tarmo (2014). Identification of a Static Tool Force Model for Robotic Face Milling, 2014 IEEE/ASME 10th International Conference on Mechatronic and Embedded Systems and Applications(MESA). IEEE (Institute of Electrical and Electronics Engineers). ISSN 9781479922802. doi: 10.1109/MESA.2014.6935591.
• Pawlus, Witold Pawel; Choux, Martin Marie Hubert; Hovland, Geir & Huynh, Khang (2014). Parameters Identification of Induction Motor Dynamic Model for Offshore Applications, 2014 IEEE/ASME 10th International Conference on Mechatronic and Embedded Systems and Applications(MESA). IEEE (Institute of Electrical and Electronics Engineers). ISSN 9781479922802. doi: 10.1109/MESA.2014.6935555.
• Luxcey, Neil; Reinholdtsen, Svein-Arne; Sauder, Thomas Michel; Fouques, Sébastien; Jin, Jingzhe & Kauczynski, Wojciech [Vis alle 7 forfattere av denne artikkelen] (2014). Influence of wave-induced skid motions on the launch of free-fall skid lifeboats from floating hosts: experimental and numerical investigations, 33rd International Conference on Ocean, Offshore and Arctic Engineering Volume 4B: Structures, Safety and Reliability. The American Society of Mechanical Engineers (ASME). ISSN 978-0-7918-4543-1. doi: 10.1115/OMAE2014-24644. Vis sammendrag

  The evacuation of personnel from offshore installations in severe weather conditions is generally ensured by free-fall lifeboats. Their performance can be assessed by means of numerical simulations to estimate accelerations loads on occupants, structural loads on the lifeboat hull, as well as forward speed after water-exit. These parameters strongly depend on the water entry conditions of the lifeboat, which in turn are very sensitive to the previous phases of the launch that starts on the skid. On floating production, storage and offloading (FPSO) vessels in the Norwegian Sea, lifeboats are often installed on skids at the bow so that waves may induce large skid motions with typical extreme vertical amplitude of fifteen to twenty meters in a 100-year storm condition. Moreover, wave-induced motions may also cause trim and list of the skid, which initiates more complex six degrees-of-freedom trajectories during free-fall. In such conditions, a proper modelling of the lifeboat trajectory on the moving skid is necessary in order to assess the performance of the lifeboat with numerical simulations. This paper investigates the effects of the wave-induced skid motion on the launch of free-fall lifeboats from floating hosts. The first part of the paper describes the six-degrees-of-freedom numerical skid model used in MARINTEK’s lifeboat launch simulator VARUNA. The second part presents two model test campaigns aimed at validating the numerical skid model. The model test results are compared to those obtained from the numerical simulations. Finally, the importance of the skid motion on the lifeboat trajectory is discussed.

• Magnussen, Øyvind; Ottestad, Morten & Hovland, Geir (2013). Experimental Validation of a Quaternion-based Attitude estimation with Direct Input to a Quadcopter Control System, Unmanned Aircraft Systems (ICUAS), 2013 International Conference On. IEEE conference proceedings. ISSN 978-1-4799-0817-2. s. 480–485. doi: 10.1109/ICUAS.2013.6564723. Vis sammendrag

  This paper presents a method to calculate the attitude quaternion of a quadcopter with few calculations. The quaternion calculation is based on accelerometers and gyroscopes from an Inertial Measurement Unit (IMU). The quaternion from the accelerometer is calculated as the shortest rotation arc from the gravity vector in the navigation frame. The quaternion from the gyroscope is calculated based on equations of the quaternion derivative. A complementary filter is combining the two quaternions with a componentwise comparison. The attitude estimation is calculated without any trigonometric functions. The quaternion is directly used as an input to the attitude controller. The attitude controller is a PD controller running at 400Hz. A model of the quadcopter in Matlab verified that the control system worked as intended. The estimator was verified with a Stewart platform, by mounting the quadcopter on top of it and comparing the angles from the Stewart platform with the angles from the filter. Finally the algorithms were implemented on a quadcopter controller board, and the attitude estimator were compared with the attitude estimation from a high-end IMU from MicroStrain. The complete control system was also tested on a 8-bit microcontroller running at 16 MHz. The relatively slow processor on the microcontroller was also able to do every calculations within 2.5ms.

• Tyapin, Ilya & Hovland, Geir (2013). Kinematic calibration method for a 5-DOF Gantry-Tau parallel kinematic machine. IEEE International Conference on Robotics and Automation (ICRA). ISSN 1050-4729. s. 4665–4670. doi: 10.1109/ICRA.2013.6631241. Vis sammendrag

  In this paper a new step-wise approach to kinematic calibration of a 5-DOF Gantry-Tau parallel kinematic machine (PKM) is presented. The approach can be adapted to the modular design of the PKM and the calibration could easily perform part of the assembly instructions for the machine. By using measurements from a laser tracker and least-squares estimates of polynomial functions, a typical accuracy of about 20 micrometer was achieved for the base actuators. The remaining set of 30 general parameters for the hexapod link structure and spherical joint connections were successfully estimated using the Complex search-based evolutionary algorithm.

• Klimchik, Alexandr; Pashkevich, Anatol; Chablat, Damien & Hovland, Geir (2013). Compliance error compensation technique for parallel robots composed of non-perfect serial chains. Robotics and Computer-Integrated Manufacturing. ISSN 0736-5845. 29(2), s. 385–393. doi: 10.1016/j.rcim.2012.09.008. Vis sammendrag

  The paper presents the compliance errors compensation technique for over-constrained parallel manipulators under external and internal loadings. This technique is based on the non-linear stiffness modeling which is able to take into account the influence of non-perfect geometry of serial chains caused by manufacturing errors. Within the developed technique, the deviation compensation reduces to an adjustment of a target trajectory that is modified in the off-line mode. The advantages and practical significance of the proposed technique are illustrated by an example that deals with groove milling by the Orthoglide manipulator that considers different locations of the workpiece. It is also demonstrated that the impact of the compliance errors and the errors caused by inaccuracy in serial chains cannot be taken into account using the superposition principle.

• Kaldestad, Knut Berg; Hovland, Geir & Anisi, David (2012). 3D Sensor-Based Obstacle Detection Comparing Octrees and Point Clouds Using CUDA. MIC Journal: Modeling, Identification and Control. ISSN 0332-7353. 33(4), s. 123–130. doi: 10.4173/mic.2012.4.1. Vis sammendrag

  This paper presents adaptable methods for achieving fast collision detection using the GPU and Nvidia CUDA together with Octrees. Earlier related work have focused on serial methods, while this paper presents a parallel solution which shows that there is a great increase in time if the number of operations is large. Two different models of the environment and the industrial robot are presented, the first is Octrees at different resolutions, the second is a point cloud representation. The relative merits of the two different world model representations are shown. In particular, the experimental results show the potential of adapting the resolution of the robot and environment models to the task at hand.

• Choux, Martin Marie Hubert; Tyapin, Ilya & Hovland, Geir (2012). Extended friction model of a hydraulic actuated system, Reliability and Maintainability Symposium (RAMS), 2012 Proceedings. IEEE conference proceedings. ISSN 978-1-4577-1851-9. doi: 10.1109/rams.2012.6175517. Vis sammendrag

  The main contribution of this paper is an experimental validation and comparison of three different friction models for an electro-hydraulic servo system. The first is the wellknown LuGre model which incorporates dynamic friction effects. The second model is based on a relatively recent publication by Yanada in 2008 [6], which incorporates liquid film thickness in the servo valve. The third model is a new contribution presented in this paper, where valve underlap and mass acceleration are combined with the LuGre model. The experimental results show that for hydraulic systems, the film thickness model is an improvement over the LuGre model, while the new model presented in this paper is an improvement over both the LuGre and the film thickness models. An accurate friction model is an important tool for reliability engineers when distinguishing maintenance related degradation from dynamic effects.

• Choux, Martin Marie Hubert; Tyapin, Ilya & Hovland, Geir (2012). Leakage-detection in blade pitch control systems for wind turbines, Reliability and Maintainability Symposium (RAMS), 2012 Proceedings. IEEE conference proceedings. ISSN 978-1-4577-1851-9. doi: 10.1109/rams.2012.6175515. Vis sammendrag

  The main contribution of the work is a systematic study evaluating the performance of different filters for leakage detection in pitch control systems. The effectiveness of the proposed methods is examined in a Matlab/Simulink real-time environment. The test bed consists of the following elements: hydraulic power unit, servo valve, two leakage bypasses, hydraulic cylinder, payload and xPC-based control system. The filters are tested with the state-augmentation and the hypothesis testing approaches. To our knowledge, the comparison of these different approaches has not been done previously for this type of application. The paper concludes on the accuracy and sensitivity of the leakage detection as well as the computational complexity and the real-time performance.

• Choux, Martin Marie Hubert; Hovland, Geir & Blanke, Mogens (2012). Cascade Controller Including Backstepping for Hydraulic-Mechanical Systems. I Imsland, Lars Struen (Red.), 2012 IFAC Workshop on Automatic Control in Offshore Oil and Gas Production : Norwegian University of Science and Technology 31.5-1.6 2012. Elsevier. ISSN 978-3-902661-99-9. doi: 10.3182/20120531-2-no-4020.00046. Vis sammendrag

  Development of a cascade controller structure including adaptive backstepping for a nonlinear hydraulic-mechanical system is considered in this paper where a dynamic friction (LuGre) model is included to obtain the necessary accuracy. The paper compares the performance of two variants of an adaptive backstepping tracking controller with earlier results. The new control architecture is analysed and enhanced tracking performance is demonstrated when including the extended friction model. The complexity of the backstepping procedure is significantly reduced due to the cascade structure. Hence, the proposed control structure is better suited to real-time implementation.

• Kaldestad, Knut Berg; Hovland, Geir & Anisi, David (2012). Obstacle Detection in an Unstructured Industrial Robotic System: Comparison of Hidden Markov Model and Expert System. I Petrovic, Ivan (Red.), Proceedings 10th IFAC Symposium on Robot Control. IFAC Papers Online. ISSN 978-3-902823-11-3. doi: 10.3182/20120905-3-hr-2030.00059. Vis sammendrag

  This paper presents a comparison of two approaches for detecting unknown obstacles inside the workspace of an industrial robot using a laser rangefinder for 2-D measurements. The two approaches are based on Expert System (ES) and Hidden Markov Model (HMM). The results presented in the paper demonstrate that both approaches are able to correctly detect and classify unknown objects. The ES is characterised by low computational requirements and an easy setup when relatively few known objects are to be included inside the workspace. HMMs are characterised by a higher flexibility and the ability to handle a larger amount of known objects inside the workspace. Another significant benefit of the HMM approach taken in this paper, in contrast to voice recognition, is the fact that the learnt parameters of the HMMs have physical meaningful geometrical interpretations.

• Haaø, Jørgen; Vangen, Steffen; Tyapin, Ilya; Choux, Martin Marie Hubert; Hovland, Geir & Hansen, Michael Rygaard (2012). The Effect of Friction in Passive and Active Heave Compensation of Crown Block Mounted Compensators. I Imsland, Lars Struen (Red.), 2012 IFAC Workshop on Automatic Control in Offshore Oil and Gas Production : Norwegian University of Science and Technology 31.5-1.6 2012. Elsevier. ISSN 978-3-902661-99-9. doi: 10.3182/20120531-2-no-4020.00040. Vis sammendrag

  This paper studies the effects of friction model during passive and active heave compensation of offshore drilling equipment. The main purpose of heave compensation while drilling from vessels or semi-submersible platforms is to maintain the drilling operation unaffected by the wave induced motion. The investigated system is of an existing crown mounted compensator. A model of the system is developed which includes mechanics, hydraulics and pneumatics. The passive heave compensation scheme is described including force equalising hydraulic cylinders. In this paper the detrimental effect of friction on the heave compensation performance in both passive and active heave compensation is investigated and discussed.

• Kjelland, Magnus Berthelsen; Hansen, Michael Rygaard; Tyapin, Ilya & Hovland, Geir (2012). Tool-Point Control for a Redundant Heave Compensated Hydraulic Manipulator. I Imsland, Lars Struen (Red.), 2012 IFAC Workshop on Automatic Control in Offshore Oil and Gas Production : Norwegian University of Science and Technology 31.5-1.6 2012. Elsevier. ISSN 978-3-902661-99-9. doi: 10.3182/20120531-2-no-4020.00034. Vis sammendrag

  In this paper, theoretical and experimental implementation of heave compensation on a redundant hydraulically actuated manipulator with 3-dof has been carried out. The redundancy is solved using the pseudo-inverse Jacobian method. Techniques for minimizing velocities and avoiding mechanical joint saturations is implemented in the null space joint motion. Model based feed-forward, combined with a PI-controller handles the velocity control of each joint.A time domain simulation model has been developed, experimentally verified, and used for controller parameter tuning. Model verification and experimental results are obtained while the manipulator is exposed to wave disturbances created in a dry environment by means of a Stewart platform.

• Kaldestad, Knut Berg; Hovland, Geir & Anisi, David (2012). CAD-Based Training of an Expert System and a Hidden Markov Model for Obstacle Detection in an Industrial Robot Environment. I Imsland, Lars Struen (Red.), 2012 IFAC Workshop on Automatic Control in Offshore Oil and Gas Production : Norwegian University of Science and Technology 31.5-1.6 2012. Elsevier. ISSN 978-3-902661-99-9. doi: 10.3182/20120531-2-no-4020.00036. Vis sammendrag

  Deploying industrial robots in harsh outdoor environments require additional functionalities not currently provided. For instance, movement of standard industrial robots are pre-programmed to avoid collision. In dynamic and less structured environments, however, the need for online detection and avoidance of unmodelled objects arises. This paper focus on online obstacle detection using a laser sensor by proposing three different approaches, namely a CAD-based Expert System (ES) and two probabilistic methods based on a Hidden Markov Model (HMM) which requires observation based training. In addition, this paper contributes by providing a comparison between the CAD-based ES and the two versions of the HMM, one trained with real sensor data, and one where virtual sensor data has been extracted from the CAD-model and used during the training phase.

• Cibulka, Jaroslav; Ebbesen, Morten Kjeld; Hovland, Geir; Robbersmyr, Kjell G & Hansen, Michael Rygaard (2012). A Review on Approaches for Condition Based Maintenance in Applications with Induction Machines Located Offshore. MIC Journal: Modeling, Identification and Control. ISSN 0332-7353. 33(2), s. 69–86. doi: 10.4173/mic.2012.2.4. Vis sammendrag

  This paper presents a review of different approaches for Condition Based Maintenance (CBM) of induction machines and drive trains in offshore applications. The paper contains an overview of common failure modes, monitoring techniques, approaches for diagnostics, and an overview of typical maintenance actions. Although many papers have been written in this area before, this paper puts an emphasis on recent developments and limits the scope to induction machines and drive trains applied in applications located offshore.

• Kjelland, Magnus Berthelsen; Hansen, Michael Rygaard; Tyapin, Ilya & Hovland, Geir (2012). Tool-Point Control of a Planar Hydraulically Actuated Manipulator with Compensation of Non-Actuated Degree of Freedom, 2012 12th International Conference on Control, Automation and Systems, Proceedings. IEEE conference proceedings. ISSN 978-89-93215-04-5. s. 672–677. Vis sammendrag

  The current work is on motion control of a hydraulically actuated manipulator with a view to handle offshore payload transfer between moving frames. The manipulator has redundant actuation and also, a non-actuated degree of freedom. The motion control has two targets: tool point control and compensation of the non-actuated degree of freedom. The redundancy is handled by means of pseudo-inverse kinematics while optimizing a cost function, avoiding mechanical joint limits. The compensation of the un-actuated degree of freedom employs LQR control, minimizing position and velocity error while maintaining the tracking reference for the tool-point. The proposed control scheme is implemented and experimentally validated in a practical system where the manipulator is mounted on a Stewart platform that allows for the simulation of wave induced heave motion as a disturbance.

• Tyapin, Ilya; Hovland, Geir & Jorde, Jørgen (2011). Comparison of Markov Theory and Monte Carlo Simulations for Analysis of Marine Operations Related to Installation of an Offshore Wind Turbine. I Singh, Maneesh; Raj B. K. N., Rao & Liyanage, Jayantha Prasanna (Red.), Proceedings of the 24th International Congress on Condition Monitoring and Diagnostics Engineering Management (COMADEM2011). COMADEM International. ISSN 0-9541307-2-3. s. 1071–1081. Vis sammendrag

  This paper contains a comparison study of two different methods for estimating weather downtime and duration of marine operations related to the installation of bottom-fixed offshore wind turbines. The first method is based on numerical Monte Carlo simulations. The second method is based on an approach using Markov theory as published in (Anastasiou and Tsekos, 1996), and it differs from the Monte Carlo technique in that it establishes analytically, not through simulation, the probability distribution of the duration of the marine operations. Having established the probability distribution of individual activities in the operations scenario, the probability distribution of the duration of an entire marine operation is determined with the aid of the Probabilistic Network and Evaluation Technique (PNET), see (Ang et al., 1975). The combination of Markov theory and PNET provides a useful means for predicting the duration of a marine operation. Both activities which do and do not require a weather window are included in the analysis, as well as the possibility to execute activities as a combination of parallel and sequential operations. A comparison of the computational time efforts using the analytical approach and Monte Carlo simulation are presented in in this paper, where Markov theory based approach is several times faster than Monte Carlo simulations. The paper includes an illustrative example related to the installation process of bottom-fixed offshore wind turbines.. The sea state generator used in the example is based on observed weather data for the North Sea. The paper concludes with a summary of advantages and disadvantages of the two approaches based on Monte Carlo simulations and Markov Theory/PNET.

• Alabakhshizadeh, Abozar; Iskandarani, Yousef; Hovland, Geir & Midtgård, Ole-Morten (2011). Analysis, Modeling and Simulation of Mechatronic Systems using the Bond Graph Method. MIC Journal: Modeling, Identification and Control. ISSN 0332-7353. 32(1), s. 35–45. doi: 10.4173/mic.2011.1.3. Vis sammendrag

  The Bond Graph is the proper choice of physical system used for: (i) Modeling which can be applied to systems combining multidisciplinary energy domains, (ii) Analysis to provide a great value proposition for finding the algebraic loops within the system enabling the process of troubleshooting and eliminating the defects by using the proper component(s) to fix the causality conflict even without being acquainted in the proper system, and (iii) Simulation facilitated through derived state space equations from the Bond Graph model is solved using industrial simulation software, such as 20-Sim. The Bond Graph technique is a graphical language of modeling, in which component energy ports are connected by bonds that specify the transfer of energy between system components. Following a brief introduction of the Bond Graph methodology and techniques, two separate case studies are comprehensively addressed. The first case study is a systematic implementation of a fourth order electrical system and conversion to mechanical system while the second case study presents modeling of the Dielectric Electro Active Polymer (DEAP) actuator. Building the systematic Bond Graph of multifaceted system and ease of switching between different domains are aims of the first case study while the second study shows how a complex mechatronic system could be analyzed and built by the Bond Graph. The respective Bond Graphs in each case is evaluated in the light of mathematical equations and simulations. Excellent correlation has been achieved between the simulation results and proper system equations.

• Tyapin, Ilya & Hovland, Geir (2011). The Gantry-Tau parallel kinematic machine-kinematic and elastodynamic design optimisation. Meccanica (Milano. Print). ISSN 0025-6455. 46(1), s. 113–129. doi: 10.1007/s11012-010-9394-9.
• Murray, Matthew; Hovland, Geir & Brogårdh, Torgny (2011). Optimised assembly mode reconfiguration of the 5-DOF Gantry-Tau using mixed-integer programming. Meccanica (Milano. Print). ISSN 0025-6455. 46(1), s. 101–111. doi: 10.1007/s11012-010-9404-y.
• Tyapin, Ilya & Hovland, Geir (2010). Multi-Objective Design Optimisation of a Class of PKMs - The 3-DOF Gantry-Tau. Proceedings of the IASTED International Conference on Modelling, Identification, and Control (MIC). ISSN 1025-8973. s. 255–262. Vis sammendrag

  The main contribution of this paper is the use of the evolutionary multi-objective methodology based on the complex search algorithm and geometric approaches to optimise a parallel kinematic structure. The design optimisation scheme includes the kinematic (collisions free workspace), elastostatic (Cartesian stiffness in the Y direction) and elastodynamic (first resonance frequency) properties of the PKM as the objectives. The optimisation constraints are the support frame lengths, actuator positions, end-effector?s kinematic parameters and the robot?s arm lengths. The optimisation results are presented in this paper.

• Choux, Martin Marie Hubert & Hovland, Geir (2010). Adaptive Backstepping Control of Nonlinear Hydraulic-Mechanical System Including Valve Dynamics. MIC Journal: Modeling, Identification and Control. ISSN 0332-7353. 31(1), s. 35–44. doi: 10.4173/mic.2010.1.3. Vis sammendrag

  The main contribution of the paper is the development of an adaptive backstepping controller for a nonlinear hydraulic-mechanical system considering valve dynamics. The paper also compares the performance of two variants of an adaptive backstepping tracking controller with a simple PI controller. The results show that the backstepping controller considering valve dynamics achieves significantly better tracking performance than the PI controller, while handling uncertain parameters related to internal leakage, friction, the orifice equation and oil characteristics.

• Breivik, Morten; Hovland, Geir & From, Pål Johan (2009). Trends in Research and Publication: Science 2.0 and Open Access. MIC Journal: Modeling, Identification and Control. ISSN 0332-7353. 30(3), s. 181–190. Vis sammendrag

  This paper presents recent trends in scientific publication and research as seen from the research fields of modeling, identification and control (MIC). The topic of Open Access (OA) publication and the effect OA has on citations and funding mechanisms have received particular attention. The paper includes a statistical survey of 50 journals and the most cited papers during the last decade in fields close to MIC. In addition, new mechanisms for user-generated contents and social-networking sites are described.

• Tyapin, Ilya & Hovland, Geir (2009). Kinematic and Elastostatic Design Optimisation of the 3-DOF Gantry-Tau Parallel Kinematic Manipulator. MIC Journal: Modeling, Identification and Control. ISSN 0332-7353. 30(2), s. 39–56. doi: 10.4173/mic.2009.2.1. Vis sammendrag

  One of the main advantages of the Gantry-Tau machine is a large accessible workspace/footprint ratio compared to many other parallel machines. The Gantry-Tau improves this ration further by allowing a change of assembly mode without internal link collisions or collisions between the links and end-effector. The reconfigurable Gantry-Tau kinematic design obtained by multi-objective optimisation according to this paper gives the following features: 3-D workspace/footprint ratio is more than 3.19, lowest Cartesian stiffness in the workspace is

• Choux, Martin; Karimi, Hamid Reza; Hovland, Geir; Hansen, Michael Rygaard; Ottestad, Morten & Blanke, Mogens (2009). Robust Adaptive Backstepping Control Design for a Nonlinear Hydraulic-Mechanical System, Proceedings of the 48th IEEE Conference on Decision and Control, Shanghai. IEEE conference proceedings. ISSN 978-1-4244-3872-3. s. 2460–2467. Vis sammendrag

  The complex dynamics that characterize hydraulic systems make it difficult for the control design to achieve prescribed goals in an efficient manner. In this paper, we present the design and analysis of a robust nonlinear controller for a Nonlinear Hydraulic-Mechanical (NHM) System. The system consistes in an electrohydraulic servo valve and two hydraulic cylinders. Specifically, by considering a part of the dynamics of the NHM system as a norm-bounded uncertainty, two adaptive controllers are developed based on the backstepping technique that ensure the tracking error signals asymptotically converge to zero despite the uncertainties in the system according to the Barbalat lemma. The resulting controllers are able to take into account the interval uncertainties in Coulomb friction parameters and in the internal leakage parameters in the cylinders. Two adaptation laws are obtained by using the Lyapunov functional method and inequality techniques. Simulation results demonstrate the performance and feasibility of the proposed method.

• Hovland, Geir (2008). Evaluation of an online inverted pendulum control experiment. IEEE Transactions on Education. ISSN 0018-9359. 51(1), s. 114–122. doi: 10.1109/TE.2007.906612. Vis sammendrag

  This paper presents an evaluation of the inverted pendulum experiment in control engineering from a statistical and pedagogical point of view. Student usage statistics and success rates were collected over a period of three years at the University of Queensland, Brisbane, Australia. The results in the paper show that an online experiment can both increase student satisfaction and success rate while decreasing the costs to the university associated with a traditional laboratory setup. In particular, the number of laboratory benches has been reduced from seven to one. At the same time the number of laboratory contact hours for the course administrator was more than halved.

• Brogårdh, Torgny & Hovland, Geir (2008). The Tau PKM Structures, Smart Devices and Machines for Advanced Manufacturing. Springer Publishing Company. s. 79–110. Vis sammendrag

  In this paper a new family of PKM structures based on the Tau concept is described. It is shown that the non-symmetrical Tau link structures solve the problem of obtaining a large accessible work space in relation to the footprint of a PKM and examples of large work space Tau PKMs are given both for rotating and linear actuators. Some results are presented from an investigation of the SCARA Tau manipulator with respect to its work space and elastodynamical properties, showing its potential for applications with high performance requirements. The main part of the paper is about the Gantry Tau manipulator, which is based on the same non-symmetrical link structure as the SCARA Tau manipulator. It is shown that this manipulator will get a large accessible work space, that it can be reconfigured to increase the work space further, that it can be calibrated to non-parallel linear guide-ways and that it can be designed for very high stiffness and bandwidth. The nominal kinematics as well as the kinematics with non parallel linear guide ways are derived and the stiffness is calculated using the duality between the statics and the link Jacobian for a PKM. The mechanical bandwidth calculations are based on a new method with mass-spring-damper link models. With the promising performance results obtained with the Tau family of manipulators, the potential for the use of these in industry is discussed.

• Tyapin, Ilya; Hovland, Geir & Brogårdh, Torgny (2007). Workspace optimisation of a reconfigurable parallel kinematic manipulator, Proceedings of the 2007 IEEE/ASME International Conference on Intelligent Advanced Mechatronics. IEEE conference proceedings. s. 1–6. Vis sammendrag

  One significant limitation of parallel kinematic machines in the past has been the limited workspace to installation space ratio. The Gantry-Tau is an example of a relatively new PKM which improves this ratio by allowing a change of assembly mode without internal link collisions or collisions between the links and the moving TCP platform. The avoidance of these internal collisions is made possible by using a triangular-mounted link pair. This paper introduces for the first time the unreachable workspace for the Gantry-Tau. The unreachable area can occur in the middle of the workspace of reconfigurable PKMs with fixed length actuators. It is important to eliminate unreachable areas when designing the Gantry-Tau PKM because they appear in the middle of the workspace which is often the most useful part of the workspace. A geometric approach which describes both the reachable and unreachable workspace has been developed. This approach is significantly faster than analytical workspace calculation methods based on the inverse kinematics. Because of the fast computational speed of the geometric approach presented in this paper, the method is an ideal candidate for inclusion in a design optimisation framework. An optimised kinematic design of the Gantry-Tau is presented in the paper.

• Hovland, Geir; Murray, Matthew & Brogårdh, Torgny (2007). Experimental verification of friction and dynamic models of a parallel kinematic machine, Proceedings of the 2007 IEEE/ASME Advanced Intelligent Mechatronics International Conference. IEEE conference proceedings. s. 1–6. Vis sammendrag

  The Gantry-Tau is a parallel kinematic manipulator (PKM) that overcomes the workspace limitations of typical PKMs, while retaining PKM benefits such as small moving masses and high stiffness. An experimental verification of the dynamics of the Gantry-Tau is presented for the first time in this paper. A new friction model based on axial forces in the links of the 3-DOF Gantry-Tau combined with a recent inverse dynamics model for parallel kinematic machines is also presented and verified experimentally. The inverse dynamics model combining the friction model and the Jacobians shows a good match to the measured linear actuator forces from a full-scale prototype machine.

Se alle arbeider i Cristin

• Wyckaert, Sébastien; Røsjordet, Jan Fredrik; Bergstøl, Hanne; Lyngroth, Tomas; Auen, Andreas & Aune, Teodor N. [Vis alle 10 forfattere av denne artikkelen] (2023). Calibration of a Translational 3-DOF Parallel Kinematic Machine using Full Pose Measurements and Mechanical Adjustments. International Conference on Control, Mechatronics and Automation. ISSN 2837-5114. doi: 10.1109/ICCMA59762.2023.10374825. Vis sammendrag

  This paper presents a complete calibration method for a translational Parallel Kinematic Machine (PKM) with three degrees of freedom (DOF). The method takes advantage of the geometric specificities of this type of machine to easily compute the kinematic parameters from full pose measurements. The work presented here also includes a process to mechanically adjust the machine in order to reduce the rotational error, unlike other calibration methods where the results are only used in software to compensate for the positional errors. The inaccuracies of the linear actuators are also measured and included into the kinematic model of the machine to allow for a better compensation of the errors. The effectiveness of the procedure has been verified by experiments on a specific PKM prototype, but the method may also be applied to other configurations of translational 3-DOF PKMs.

• Jha, Ajit; Subedi, Dipendra; Løvsland, Per-Ove; Tyapin, Ilya; Cenkeramaddi, Linga Reddy & Beferull-Lozano, Baltasar [Vis alle 7 forfattere av denne artikkelen] (2020). Autonomous mooring towards autonomous maritime navigation and offshore operations.
• Pawlus, Witold; Frick, Damian; Morari, Manfred; Hovland, Geir & Choux, Martin Marie Hubert (2015). Drivetrain Design Optimization for Electrically Actuated Systems via Mixed Integer Programing.
• Pawlus, Witold; Ebbesen, Morten Kjeld; Hansen, Michael Rygaard; Choux, Martin Marie Hubert & Hovland, Geir (2015). Comparative Analysis of Numerical Models of Pipe Handling Equipment Used in Offshore Drilling Applications.
• Pawlus, Witold; Hansen, Michael Rygaard; Hovland, Geir & Choux, Martin Marie Hubert (2015). Torque Peak Reduction and Overload Monitoring of Induction Motors in Offshore Drilling Operations.
• Pawlus, Witold; Inouva, Ivar C.; Øydna, Søren; Wroldsen, Torstein Kurt & Hovland, Geir (2015). Next Generation Hardware-in-the-Loop Simulation Enables Advanced Testing of Offshore Hydraulic Systems.
• Hovland, Geir Edvin (2015). SFI Offshore Mechatronics Website. Vis sammendrag

  Website for SFI Offshore Mechatronics

• Luxcey, Neil; Reinholdtsen, Svein-Arne; Sauder, Thomas Michel; Fouques, Sébastien; Jin, Jingzhe & Kauczynski, Wojciech [Vis alle 7 forfattere av denne artikkelen] (2014). Influence of wave-induced skid motions on the launch of free-fall skid lifeboats from floating hosts: experimental and numerical investigations.
• Hovland, Geir; Choux, Martin; Murray, Matthew; Tyapin, Ilya & Brogårdh, Torgny (2008). The Gantry-Tau ¿ Summary of Latest Development at ABB, University of Agder and University of Queensland. Vis sammendrag

  The Gantry-Tau is a PKM structure having a large accessible work space in relation to its footprint. In this paper some of the features of the Gantry-Tau structure will be described and a summary of some results will be presented from the analysis of the kinematic, elastostatic and elastodynamic properties of the PKM. In the case of kinematics a 5 axes Gantry-Tau will be described as well as methods for the calibration and reconfiguration of the structure. For the elastostatic and elastodynamic analysis a method assuming that each PKM link can be described as a mass-spring-damper model will be presented. A new design optimisation scheme taking the kinematic and elastostatic properties into account will also summarized.

• Choux, Martin & Hovland, Geir (2008). Design of A Hydraulic Servo System for Robotic Manipulation. Vis sammendrag

  In this document the design, control and simulation of a hydraulic model for grasping an object is presented. The principal equations that constraint such a system are first investigated through the presentation of the hydraulic components which constitute the model. Their intrinsic characteristics are discussed as well as their interactions with each other. The controller that best fit this application is found to be a hybrid position/force control where the external forces are considered as a disturbance. In the last part of this document the model is simulated with more realistic component parameters including Stribeck effect friction, leakage and nonlinear valve characteristics. The results found with this simplified model show good correlation with the more realistic simulated environment.

• Hovland, Geir; Brogårdh, Torgny & Tyapin, Ilya (2008). Kinematic and Elastodynamic Design Optimisation of the 3-DOF Gantry-Tau Parallel Kinematic Manipulator. Vis sammendrag

  One of the main advantages of the Gantry-Tau machine is a large accessible workspace/footprint ratio compared to many other parallel machines. The Gantry-Tau improves this ratio by allowing a change of assembly mode without internal link collisions or collisions between the links and the moving TCP platform. However, the optimal kinematic, elastostatic and elastodynamic design parameters of the machine are still difficult to calculate and this paper introduces an optimisation scheme based on the geometric approach for the workspace area and the functional dependencies of the elements of the static matrix and the Laplace transform to define the first resonance frequency. The method to calculate the first resonance stiffness assumes that each link and universal joint can be described by a mass-springdamper model and calculates the transfer function from a Cartesian force or torque to Cartesian position or orientation. These approaches are significantly faster than analytical methods based on the inverse kinematics or the general Finite Elements Method (FEM). Kinematic design obtained by optimisation according to this paper gives a workspace/footprint ratio of more than 2.7 and the first resonance frequency of more than 50 Hz with components of an existing lab prototype at the University of Agder.

• Hovland, Geir; Brogårdh, Torgny & Murray, Matthew (2008). Singularity-Free Reconfiguration of the 5-DOF Gantry-Tau Parallel Kinematic Machine. Vis sammendrag

  This paper presents a systematic approach based on Mixed Integer Linear Programming for finding a near optimal singularity-free reconfiguration path of the 5-DOF Gantry-Tau parallel kinematic machine. The results in the paper demonstrate that singularity-free reconfiguration (change of assembly mode) of the machine is possible, which significantly increases the usable workspace. The method has been applied to a full-scale prototype and the singularity-free path has been verified both in simulations and with physical experiments using real-time control of the prototype.

• Hovland, Geir (2008). Robotisert Maskinering. Vis sammendrag

  Robotisert maskinering er et kostnadseffektiv alternativ til 5-akse CNC maskiner. En industrirobot har typisk et mye større arbeidsområde sammenligned med en 5-akse CNC maskin, i tillegg til en sjette akse som gjør det lettere å orientere verktøyet og komme til vanskelige og trange områder. Roboten kan også utvides med rotasjonsbord eller bli plassert på en lineærbane for ytterligere å øke arbeidsområdet. En ulempe med industriroboter sammenligned med CNC maskiner, er en lavere mekanisk stivhet. Dette gjør at industriroboter ikke kan benyttes for maskinering av harde metaller, for eksempel stål. En industrirobot kan likevel maskinere mykere materialer så som skumplast, tre, kompositter, glassfiber, kjeramikk og aluminium. Typiske industrier for robotisert maskinering er marin (produksjon av former og plugger i skumplast), flyindustrien (kompositter), møbel (tre) og bilindustrien (lette metaller). RobotStudio er et 3D grafisk simuleringsverktøy for offline programmering av ABB roboter. Denne programvaren er veldig nyttig for testing av verktøybanene for rekkevidde og kollisjoner før banene blir overført til den fysiske roboten. Programvaren IRBCAM kombinerer ABB roboter med CAD/CAM programvare, for eksempel SurfCAM, som normalt assosieres med CNC maskiner. Ved å bruke programvare fra IRBCAM og SurfCAM, ABB roboter kan nå programmeres direkte fra 3D CAD filer. Typiske CAD format som støttes er IGES, ACIS SAT og AutoCAD DWG files. Robotic milling is a cost-efficient alternative to 5-axis CNC machines. An industrial robot typically has a much larger workspace compared to a 5-axis CNC machine, in addition to the 6th robot axis which makes it easier to re-orient the tool and get access to difficult and narrow areas. The robot can also be extended with rotary tables or be placed on an external linear track to increase to workspace area even further. One drawback of industrial robots compared to CNC machines, is a lower mechanical stiffness. Hence, a standard industrial robot can not be used for machining in hard metals, such as steel. However, an industrial robot can easily machine softer materials such as foam, wood, composites, glass fibres, ceramics and aluminium. Some common industries for robotic milling applications are marine (manufacture of moulds and plugs in foam), aerospace (composites), furniture (wood) and automotive (light metals). RobotStudio is a 3D graphical simulation engine for offline programming of ABB robots. This software is invaluable for testing the toolpaths for reachability and collisions before transferring the toolpath to the real robot. The company IRBCAM has taken the next step and combined ABB robots with CAD/CAM software such as SurfCAM which is typically associated with CNC machines. By using software from IRBCAM and SurfCAM, ABB robots can now be programmed for rapid prototyping directly from 3D CAD files. Typical CAD formats which are supported are IGES, ACIS SAT and AutoCAD DWG files.

• Hovland, Geir (2007). Roboter hindrer utflagging.
• Hovland, Geir (2007). A Geometrical Method for Calculating the Unreachable Workspace of the 3-DOF Gantry-Tau Parallel Manipulator. Vis sammendrag

  One of the main advantages of the Gantry-Tau machine is a large accessible workspace/footprint ratio compared to many other parallel machines. The Gantry-Tau improves this ratio by allowing a change of assembly mode without internal link collisions or collisions between the links and the moving TCP platform. This paper introduces the geometric approach for the unreachable workspace area for the Gantry-Tau. The unreachable area can occur in the middle of the workspace of reconfigurable PKMs with fixed length actuators. It is important to eliminate unreachable areas when designing the Gantry-Tau PKM because they appear in the middle of the workspace which is often the most useful part of the workspace. This approach is significantly faster than analytical workspace calculation methods based on the inverse kinematics. Because of the fast computational speed of the geometric approach, the method is ideal for inclusion in a design optimisation framework. The design presented in this paper achieves a workspace/footprint ratio of more than 2.7 with a zero unreachable workspace. Typical PKMs, for example the Delta robot, has a ratio less than one. In addition, a workspace optimisation method is presented where the parameters are the support frame lengths and the robot¿s arm lengths.

• Hovland, Geir & Robbersmyr, Kjell G. (2007). A Survey of Mechatronics Education in the Nordic and Baltic Countries. Vis sammendrag

  This paper describes mechatronics education programs in terms of the extent to which mechatronic courses are developed and their course content emphasis (i.e., electrical/computer engineering vs mechanical engineering and system courses vs analytical courses). A selective survey of some mechatronics education programs in the Nordic and Baltic countries is presented and the programs are compared. The survey revealed that the investigated universities have self-contained mechatronic departments with research activity and their programs are optimized from a mechatronics point of view. The small universities focus their education towards the local industry, while the larger universities¿ programs are more general.

• Hovland, Geir (2007). Workspace Optimisation of a Reconfigurable Parallel Kinematic Manipulator. Vis sammendrag

  One significant limitation of parallel kinematic machines in the past has been the limited workspace to installation space ratio. The Gantry-Tau is an example of a relatively new PKM which improves this ratio by allowing a change of assembly mode without internal link collisions or collisions between the links and the moving TCP platform. The avoidance of these internal collisions is made possible by using a triangular-mounted link pair. This paper introduces for the first time the unreachable workspace for the Gantry-Tau. The unreachable area can occur in the middle of the workspace of reconfigurable PKMs with fixed length actuators. It is important to eliminate unreachable areas when designing the Gantry-Tau PKM because they appear in the middle of the workspace which is often the most useful part of the workspace. A geometric approach which describes both the reachable and unreachable workspace has been developed. This approach is significantly faster than analytical workspace calculation methods based on the inverse kinematics. Because of the fast computational speed of the geometric approach presented in this paper, the method is an ideal candidate for inclusion in a design optimisation framework. An optimised kinematic design of the Gantry-Tau is presented in the paper.

• Hovland, Geir (2007). Experimental Verification of Friction and Dynamic Models of a Parallel Kinematic Machine. Vis sammendrag

  The Gantry-Tau is a parallel kinematic manipulator (PKM) that overcomes the workspace limitations of typical PKMs, while retaining PKM benefits such as small moving masses and high stiffness. An experimental verification of the dynamics of the Gantry-Tau is presented for the first time in this paper. A new friction model based on axial forces in the links of the 3-DOF Gantry-Tau combined with a recent inverse dynamics model for parallel kinematic machines is also presented and verified experimentally. The inverse dynamics model combining the friction model and the Jacobians shows a good match to the measured linear actuator forces from a full-scale prototype machine.

• Dybedal, Joacim & Hovland, Geir (2023). 3D Sensor Placement and Embedded Processing for People Detection in an Industrial Environment. Universitetet i Agder. ISSN 978-82-8427-150-7. Fulltekst i vitenarkiv Vis sammendrag

  At a time when autonomy is being introduced in more and more areas, computer vision plays a very important role. In an industrial environment, the ability to create a real-time virtual version of a volume of interest provides a broad range of possibilities, including safety-related systems such as vision based anti-collision and personnel tracking. In an offshore environment, where such systems are not common, the task is challenging due to rough weather and environmental conditions, but the result of introducing such safety systems could potentially be lifesaving, as personnel work close to heavy, huge, and often poorly instrumented moving machinery and equipment. This thesis presents research on important topics related to enabling computer vision systems in industrial and offshore environments, including a review of the most important technologies and methods. A prototype 3D sensor package is developed, consisting of different sensors and a powerful embedded computer. This, together with a novel, highly scalable point cloud compression and sensor fusion scheme allows to create a real-time 3D map of an industrial area. The question of where to place the sensor packages in an environment where occlusions are present is also investigated. The result is algorithms for automatic sensor placement optimisation, where the goal is to place sensors in such a way that maximises the volume of interest that is covered, with as few occluded zones as possible. The method also includes redundancy constraints where important sub-volumes can be defined to be viewed by more than one sensor. Lastly, a people detection scheme using a merged point cloud from six different sensor packages as input is developed. Using a combination of point cloud clustering, flattening and convolutional neural networks, the system successfully detects multiple people in an outdoor industrial environment, providing real-time 3D positions. The sensor packages and methods are tested and verified at the Industrial Robotics Lab at the University of Agder, and the people detection method is also tested in a relevant outdoor, industrial testing facility. The experiments and results are presented in the papers attached to this thesis.

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