Morten Kjeld Ebbesen

• Bhola, Mohit; Andersen, Torben Ole & Ebbesen, Morten Kjeld (2023). Design of Novel Closed-Circuit Hydrostatic Transmission without Charge Pump. I Barth, Eric J. (Red.), Fluid Power Systems Technology. The American Society of Mechanical Engineers (ASME). ISSN 9780791887431. Vis sammendrag

  This paper deals with the design of the control system for novel two-pumps one-motor (TPOM) systems for applications which require the deployment of a closed-circuit hydro-static transmission (HST). In conventional closed-circuit HST, the charge/booster pump is an integral part of the main pump used to compensate the leakages occurring in the circuit in order to maintain the lowest system pressure to avoid cavitation. The charge/booster pump in the closed-circuit HST is a source of constant power loss and increases heat load in the system. This reduces the efficiency of the transmission at part load operation. Also, the lowest system pressure in the conventional circuit is held constant by the relief valve deployed at the charge pump outlet. Hence, the stiffness of the system cannot be controlled based upon the transmission working condition. To overcome this limitation and enhancing transmission efficiency, the TPOM system is designed and evaluated without changing the basic functionality of the closed-circuit transmission. In TPOM, one of the displacement machines driven by permanent magnet synchronous motors (PMSM) works in open-circuit configuration and the other in closed-circuit configuration, without the need of a charge/booster pump. The TPOM is capable to operate in four-quadrants and capable to regenerate the energy during assistive load condition. This arrangement does not require the need of pilot pressure for varying the displacement of pump and motor, which generally is supplied by a booster/charge pump in a conventional closed-circuit transmission. However, innovative use of a hydraulic intensifier is proposed for the fulfilment of pilot pressure requirements. The feasibility in control shows the energy-saving potential of the HST without booster/charge pump

• Mamo, Mebaye Belete; Ebbesen, Morten Kjeld & Poursina, Mohammad (2023). Closed-Form Dynamic Model of Planar Multilink Flexible Manipulator. I IEEE, . (Red.), IECON 2023- 49th Annual Conference of the IEEE Industrial Electronics Society. IEEE (Institute of Electrical and Electronics Engineers). ISSN 979-8-3503-3182-0. doi: 10.1109/IECON51785.2023.10312080.
• Mamo, Mebaye Belete; Ebbesen, Morten Kjeld & Poursina, Mohammad (2023). Dynamic Modelling and Simulation of Two-link Flexible Robot Using Rayleigh Beam Theory . I Zhou, Jing (Red.), 2023 11th International Conference on Control, Mechatronics and Automation (ICCMA). IEEE conference proceedings. ISSN 979-8-3503-1568-4. s. 164–170. doi: 10.1109/ICCMA59762.2023.10374812.
• Zhao, Wei; Ebbesen, Morten Kjeld & Andersen, Torben Ole (2023). Comparative Analysis of Energy Efficiency: Knuckle Boom Crane Driven by Motor-Controlled Cylinders Versus Valve-Controlled Cylinders. I Zhou, Jing (Red.), 2023 11th International Conference on Control, Mechatronics and Automation (ICCMA). IEEE conference proceedings. ISSN 979-8-3503-1568-4. s. 201–207. doi: 10.1109/ICCMA59762.2023.10374706. Vis sammendrag

  When a hydraulic differential cylinder is directly connected to fixed-displacement hydraulic pumps driven by independent electric servo motors, the cylinder motion is manipulated by controlling the velocities of the electric servo motors. This configuration is called a motor-controlled hydraulic cylinder (MCC) in this study. In contrast to valve-controlled hydraulic cylinders (VCCs), MCCs theoretically offer enhanced energy efficiency due to the absence of valve throttling. However, the energy efficiency performance of MCCs in multi-cylinder applications still needs to be explored in the existing research. This paper seeks to bridge this gap by comparing a knuckle boom crane driven by proposed two-motor-two-pump MCCs with a passive load-holding function and VCCs on the crane in energy efficiency. To achieve this, non-linear dynamic models of a knuckle boom crane driven by two-motor-two-pump MCCs and the original VCCs on the crane are created in MATLAB/Simulink. A realistic operation path for lifting a payload is designed, and three load cases are tested. Simulation results demonstrate better performance of the proposed MCCs in energy efficiency than VCCs. In conclusion, this study showcases the viability of the proposed MCCs for practical applications, highlighting their enhanced energy efficiency compared to traditional VCCs.

• Farsakoglou, Thomas; Pedersen, Henrik C.; Ebbesen, Morten Kjeld & Andersen, Torben O. (2023). Determining the Optimal Number of Pistons for Offshore Digital Winch Drives. Energies. ISSN 1996-1073. 16(21). doi: 10.3390/en16217371. Fulltekst i vitenarkiv Vis sammendrag

  In offshore winch drive applications, determining the required number of pistons in digital displacement motors is critical for minimizing torque ripples. Digital displacement motors have shown promise for improving energy efficiency for offshore operations, such as placing equipment on the seabed or mineral drilling. However, they are known for exhibiting significant torque ripples, which can affect load-handling precision. This paper estimates the required number of pistons for realizing a digital hydraulic winch drive based on information from a commercial winch. The proposed drive employs full-stroke displacement strategies at high speeds and partial-stroke at low speeds. By simulating steady-state operations, this study correlates torque output with position oscillations. The results show that 37 pistons are required to keep position oscillations below a benchmark threshold of 10 mm throughout the drive’s operating range to avoid hindering the drive’s performance. However, such a high piston count could result in high costs due to the large, expensive valves required for partial-stroke operations. Therefore, this paper suggests an alternative drive topology for future research, which could potentially reduce the number of pistons that are operated with partial strokes.

• Zhao, Wei; Bhola, Mohit; Ebbesen, Morten Kjeld & Andersen, Torben Ole (2023). A Motor-Controlled Hydraulic Cylinder With Cylinder Pressure Control and Load-Holding Function - An Experimental Study. I Barth, Eric J. (Red.), Fluid Power Systems Technology. The American Society of Mechanical Engineers (ASME). ISSN 9780791887431. doi: 10.1115/FPMC2023-111712.
• Zhao, Wei; Bhola, Mohit; Ebbesen, Morten Kjeld & Andersen, Torben Ole (2023). A Novel Control Design for Realizing Passive Load-Holding Function on a Two-Motor-Two-Pump Motor-Controlled Hydraulic Cylinder. MIC Journal: Modeling, Identification and Control. ISSN 0332-7353. 44(3), s. 125–139. doi: 10.4173/mic.2023.3.3. Fulltekst i vitenarkiv Vis sammendrag

  When a hydraulic cylinder connects two chambers directly to one or two hydraulic pumps driven by electric servo motors without any control valve in between, it can be called a motor-controlled hydraulic cylinder (MCC). Unlike valve-controlled cylinders, MCCs have no valve throttling, which significantly increases the energy efficiency. Among different MCC topologies, the two-motor-two-pump (2M2P) MCC has several advantages, such as cylinder pressure control and no mode switch oscillations. However, due to state coupling when controlling both piston position and minimum cylinder chamber pressure, the 2M2P MCC is a multi-input-multi-output (MIMO) system that usually requires advanced MIMO controller analysis and design. This paper presents a control algorithm for a 2M2P MCC with the minimum cylinder pressure control and passive load-holding function. This control algorithm is tested on a single-boom crane characterized by overrunning loads. It is designed based on the analysis of the system characteristics, requiring no MIMO controller analysis and design. A non-linear model of a single-boom crane driven by the proposed 2M2P MCC is created in MATLAB/Simulink and experimentally validated. Feedback controllers are designed and verified via simulations to realize position control, minimum cylinder pressure control, and load-holding under standstill command. For a given load and speed profile, the hydraulic system efficiency during pumping and motoring mode is 55-60% and 20-25%, respectively. The system's overall efficiency can be enhanced with electrical regenerative drives, which feeds the generated power from potential energy to the grid or battery and reused in the next working cycle. The experimental results presented in this paper verifies the efficacy of the proposed control algorithm and demonstrates its superior performance in achieving the desired system response under various operating conditions.

• Farsakoglou, Thomas; Pedersen, Henrik C.; Ebbesen, Morten Kjeld & Andersen, Torben O. (2023). Improving Energy Efficiency and Response Time of an Offshore Winch Drive with Digital Displacement Motors. MIC Journal: Modeling, Identification and Control. ISSN 0332-7353. 44(3), s. 111–124. doi: 10.4173/mic.2023.3.2. Fulltekst i vitenarkiv Vis sammendrag

  Offshore winch drives require high energy efficiency and control precision, making digital displacement motors an attractive solution due to their high efficiency and potential controllability. However, the response time and the realized energy efficiency of these motors are heavily dependent on the chosen displacement control strategy, especially at low-speed operation. This paper considers various displacement control strategies to investigate whether digital displacement motors are a viable solution for offshore winch drive applications. The motor specifications are derived based on the requirements of a commercial offshore winch drive system. The analysis reveals that various displacement control strategies should be used across the drive’s operational speed range to ensure both satisfactory performance and high efficiency. Full-stroke and partial-stroke strategies are optimal for speeds above 28 rpm and 20 rpm, respectively, but unsuited for lower-speed operation. For speeds below 20 rpm, an improved sequential-stroke strategy is therefore presented. The proposed displacement control strategy provides instantaneous motor response and maintains high energy efficiency, although its robustness is slightly reduced at higher operating speeds above 20 rpm.

• Jensen, Konrad Johan; Ebbesen, Morten Kjeld & Hansen, Michael Rygaard (2022). Online Deflection Compensation of a Flexible Hydraulic Loader Crane Using Neural Networks and Pressure Feedback. Robotics. ISSN 2218-6581. 11(2). doi: 10.3390/robotics11020034. Fulltekst i vitenarkiv Vis sammendrag

  The deflection compensation of a hydraulically actuated loader crane is presented. Measurement data from the laboratory are used to design a neural network deflection estimator. Kinematic expressions are derived and used with the deflection estimator in a feedforward topology to compensate for the static deflection. A dynamic deflection compensator is implemented, using pressure feedback and an adaptive bandpass filter. Simulations are conducted to verify the performance of the control system. Experimental results showcase the effectiveness of both the static and dynamic deflection compensator while running closed-loop motion control, with a 90% decrease in static deflection.

• Jensen, Konrad Johan; Ebbesen, Morten Kjeld & Hansen, Michael Rygaard (2021). Development of 3D anti-Swing control for hydraulic knuckle boom crane. MIC Journal: Modeling, Identification and Control. ISSN 0332-7353. 42(3), s. 113–129. doi: 10.4173/mic.2021.3.2. Fulltekst i vitenarkiv Vis sammendrag

  In this paper, 3D anti-swing control for a hydraulic loader crane is presented. The difference between hydraulic and electric cranes are discussed to show the challenges associated with hydraulic actuation. The hanging load dynamics and relevant kinematics of the crane are derived to model the system and create the 3D anti-swing controller. The anti-swing controller generates a set of tool point velocities which are added to the electro-hydraulic motion controller via feedforward. A dynamic simulation model of the crane is made, and the control system is evaluated in simulations with a path controller in actuator space. Simulation results show significant reduction in the load swing angles during motion using the proposed anti-swing controller in addition to pressure feedback. Experiments are carried out to verify the performance of the anti-swing controller. Results show that the implemented pressure feedback is crucial for reaching stability, and with it the control system yields good suppression of the swing angles in practice.

• Jensen, Konrad Johan; Ebbesen, Morten Kjeld & Hansen, Michael Rygaard (2021). Novel Concept for Electro-Hydrostatic Actuators for Motion Control of Hydraulic Manipulators. Energies. ISSN 1996-1073. 14(20). doi: 10.3390/en14206566. Fulltekst i vitenarkiv Vis sammendrag

  Abstract: Self-contained hydraulic cylinders have gained popularity in the recent years but have not been implemented for high power articulated hydraulic manipulators. This paper presents a novel concept for an electro-hydrostatic actuator applicable to large hydraulic manipulators. The actuator is designed and analyzed to comply with requirements such as load holding, overload handling, and differential flow compensation. The system is analyzed during four quadrant operation to investigate energy efficiency and regenerative capabilities. Numerical simulation is carried out using path control and 2DOF anti-swing of a hydraulic crane as a load case to illustrate a real world scenario. A comparison with traditional valve-controlled actuators is conducted, showing significantly improved efficiency and with similar dynamic response, as well as the possibility for regenerating energy.

• Jensen, Konrad Johan; Ebbesen, Morten Kjeld & Hansen, Michael Rygaard (2021). Anti-swing control of a hydraulic loader crane with a hanging load. Mechatronics (Oxford). ISSN 0957-4158. 77. doi: 10.1016/j.mechatronics.2021.102599. Fulltekst i vitenarkiv Vis sammendrag

  In this paper, anti-swing control for a hydraulic loader crane is presented. The difference between hydraulic and electric cranes are discussed to show the challenges associated with hydraulic actuation. The hanging load dynamics and relevant kinematics of the crane are derived to create the 2-DOF anti-swing controller. The anti-swing controller is added to the electro-hydraulic motion controller via feedforward. A dynamic simulation model of the crane is made, and the control system is evaluated in simulations with a path controller in actuator space. Simulation results show significant reduction in the load swing angle during motion. Experiments are carried out to verify the performance of the anti-swing controller, showing good suppression of the payload angle in practice.

• Ketelsen, Søren; Michel, Sebastian; Andersen, Torben Ole; Ebbesen, Morten Kjeld; Weber, Jürgen & Schmidt, Lasse (2021). Thermo-Hydraulic Modelling and Experimental Validation of an Electro-Hydraulic Compact Drive. Energies. ISSN 1996-1073. 14(9). doi: 10.3390/en14092375. Fulltekst i vitenarkiv Vis sammendrag

  Electro-hydraulic compact drives (ECDs) are an emerging technology for linear actuation in a wide range of applications. Especially within the low power range of 5–10 kW, the plug-and-play capability, good energy efficiency and small space requirements of ECDs render this technology a promising alternative to replace conventional valve-controlled linear drive solutions. In this power range, ECDs generally rely on passive cooling to keep oil and system temperatures within the tolerated range. When expanding the application range to larger power classes, passive cooling may not be sufficient. Research investigating the thermal behaviour of ECDs is limited but indeed required for a successful expansion of the application range. In order to obtain valuable insights into the thermal behaviour of ECDs, thermo-hydraulic simulation is an important tool. This may enable system design engineers to simulate thermal behaviour and thus develop proper thermal designs during the early design phase, especially if such models contain few parameters that can be determined with limited information available. Our paper presents a lumped thermo-hydraulic model derived from the conservation of mass and energy. The derived model was experimentally validated based on experimental data from an ECD prototype. Results show good accuracy between measured and simulated temperatures. Even a simple thermal model containing only a few thermal resistances may be sufficient to predict steady-state and transient temperatures with reasonable accuracy. The presented model may be used for further investigations into the thermal behaviour of ECDs and thus toward proper thermal designs required to expand the application range.

• Ketelsen, Søren; Padovani, Damiano; Ebbesen, Morten Kjeld; Andersen, Torben Ole & Schmidt, Lasse (2020). A Gasless Reservoir Solution for Electro-Hydraulic Compact Drives With Two Prime Movers. I Johnston, Nigel (Red.), BATH/ASME 2020 Symposium on Fluid Power and Motion Control. The American Society of Mechanical Engineers (ASME). ISSN 978-0-7918-8375-4. doi: 10.1115/FPMC2020-2773. Vis sammendrag

  Due to an increased focus on improving the energy efficiency and compactness of hydraulic linear actuators, the electrohydraulic compact drive (ECD) has received increased attention lately. In this study the ECD consists of variable-speed electric motors and fixed-displacement pumps, which are directly connected to the cylinder, thus controlling the linear motion in a throttleless manner. Furthermore, ECDs are self-contained systems, i.e. based on a fully enclosed oil circuit, in order to avoid external contamination and air to enter the system and to increase system compactness. Conventionally a low-pressure gasloaded accumulator is used as an oil reservoir to compensate for the flow imbalance occurring whenever utilizing single-rod cylinders in closed systems. The accumulator pressure is to be kept relatively low to stay within the required limits governed by the permitted pump housing’s pressure. Generally, this pressure is not allowed to exceed 1-3 bar. To avoid violating this limitation, the gas volume must be significantly larger than the actual oil volume, which needs to be stored in the accumulator. This requirement decreases the obtainable compactness of the ECD, especially for systems with a large cylinder stroke. Furthermore, the accumulator represents a potential of gas leakage, which ultimately could result in the ECD being non-functional. This paper presents a gasless reservoir solution, improving the system compactness and avoiding the risk of gas leakage. The proposed solution is based on a bootstrap reservoir which is charged by the lowest cylinder chamber pressure. This strategy is feasible for the class of ECDs that is capable of controlling the lowest cylinder chamber pressure alongside the cylinder motion. An ECD consisting of two electric prime movers is considered as a case study. It is shown how the gasless reservoir may be integrated into the system, and an analysis of how this affects the operating range and the dynamic couplings of the system is presented. This leads to the derivation of a control strategy for the Multi- Input-Multi-Output (MIMO) system based on state decoupling, by defining virtual inputs to control virtual outputs. A numerical study suggests that the reservoir volume may be reduced by approximately 50% for the given system dimensions. The proposed control strategy shows good position tracking performance while also being able to control the reservoir pressure within the predefined limits of 1 to 3 bar.

• Donkov, Viktor Hristov; Andersen, Torben Ole; Linjama, Matti & Ebbesen, Morten Kjeld (2020). Digital Hydraulic Technology for Linear Actuation: A State of the Art Review. International Journal of Fluid Power. ISSN 1439-9776. 21(2). doi: 10.13052/ijfp1439-9776.2125. Vis sammendrag

  This paper analyses the current state of the art in linear actuation with digital hydraulics. Based on the differences in their aims the paper partitions the area into four actuation concepts - parallel valve solutions, single switching valve solutions, multi-chamber cylinders, and multi-pressure cylinders. The concepts are evaluated based on accuracy and smoothness of motion, switching load, reliability, efficiency and the number of components required.

• Ketelsen, Søren; Andersen, Torben Ole; Ebbesen, Morten Kjeld & Schmidt, Lasse (2020). A Self-Contained Cylinder Drive with Indirectly Controlled Hydraulic Lock. MIC Journal: Modeling, Identification and Control. ISSN 0332-7353. 41(3), s. 185–205. doi: 10.4173/MIC.2020.3.4. Fulltekst i vitenarkiv Vis sammendrag

  This paper presents a self-contained pump-controlled hydraulic linear drive including an innovative load holding sub-circuit. For safety critical applications such as crane manipulators, locking valves or load holding valves are enforced by legislation, but the load holding functionality may also be used actively to decrease the energy consumption for applications where the load is kept stationary for longer periods of time. The system proposed in this paper is based on a simple hydraulic architecture using two variable-speed electric motors each connected to a fixed-displacement pump. This architecture is well-known in academic literature, but in this paper a novel load holding sub-circuit has been included. To control this load holding functionality, the low chamber pressure needs to be controlled accurately, while still being able to control the motion of the cylinder piston as well. Due to strong cross-couplings between cylinder piston motion and chamber pressures this task is non-trivial. The control for opening the locking valves is indirect in the sense that it is controlled via the chamber pressures, which are actively controlled. The fundamental control strategy presented in this paper is based on transforming the highly coupled physical states to virtual states, significantly reducing cross-couplings.

• Jensen, Konrad Johan; Ebbesen, Morten Kjeld & Hansen, Michael Rygaard (2020). Adaptive Feedforward Control of a Pressure Compensated Differential Cylinder. Applied Sciences. ISSN 2076-3417. 10(21). doi: 10.3390/app10217847. Fulltekst i vitenarkiv Vis sammendrag

  This paper presents the design, simulation and experimental verification of adaptive feedforward motion control for a hydraulic differential cylinder. The proposed solution is implemented on a hydraulic loader crane. Based on common adaptation methods, a typical electro-hydraulic motion control system has been extended with a novel adaptive feedforward controller that has two separate feedforward states, i.e, one for each direction of motion. Simulations show convergence of the feedforward states, as well as 23% reduction in root mean square (RMS) cylinder position error compared to a fixed gain feedforward controller. The experiments show an even more pronounced advantage of the proposed controller, with an 80% reduction in RMS cylinder position error, and that the separate feedforward states are able to adapt to model uncertainties in both directions of motion.

• Donkov, Viktor Hristov; Andersen, Torben Ole & Ebbesen, Morten Kjeld (2020). An analysis of model predictive control with integral action applied to digital displacement cylinders. MIC Journal: Modeling, Identification and Control. ISSN 0332-7353. 41(3), s. 223–239. doi: 10.4173/MIC.2020.3.6. Fulltekst i vitenarkiv Vis sammendrag

  This article aims to analyze Model Predictive Control (MPC) for the control of multi-chamber cylinders. MPC with and without integral action has been introduced. Three different algorithms have been used to solve the optimization problem in the MPC. The different algorithms have been compared with an industrial solver. The influence of changing mass, choosing a different middle line pressure, system delays, signal noise, velocity estimation, and changing pressure levels has been investigated. It is concluded that for the small prediction horizon used in the paper a simple algorithm such as A* can produce results as good as the previously used Differential Evolution algorithm in less than half the time. It is further concluded that unknown software delays and unknown changes in mass have the largest effect on system performance.

• Jensen, Konrad Johan; Ebbesen, Morten Kjeld & Hansen, Michael Rygaard (2020). Development of Point-to-Point Path Control in Actuator Space for Hydraulic Knuckle Boom Crane. Actuators. ISSN 2076-0825. 9(2). doi: 10.3390/act9020027. Fulltekst i vitenarkiv
• Ketelsen, Søren; Andersen, Torben O.; Ebbesen, Morten Kjeld & Schmidt, Lasse (2019). Mass Estimation of Self-Contained Linear Electro-Hydraulic Actuators and Evaluation of the Influence on Payload Capacity of a Knuckle Boom Crane, ASME/BATH 2019 Symposium on Fluid Power and Motion Control. The American Society of Mechanical Engineers (ASME). ISSN 978-0-7918-5933-9. doi: 10.1115/FPMC2019-1689.
• Nordås, Sondre; Ebbesen, Morten Kjeld & Andersen, Torben O. (2019). Definition of Performance Requirements and Test Cases for Offshore/Subsea Winch Drive Systems With Digital Hydraulic Motors, ASME/BATH 2019 Symposium on Fluid Power and Motion Control. The American Society of Mechanical Engineers (ASME). ISSN 978-0-7918-5933-9. doi: 10.1115/FPMC2019-1670. Vis sammendrag

  A subsea crane is normally mounted on a floating vessel and equipped with a winch system. The crane can operate in water down to 3000 m. The vessel tends to move up and down due to waves. This heave motion makes offshore lifting operations challenging. In order to ease the winch operation in rough sea, the winch can be equipped with additional systems like active heave compensation and constant tension. In active heave compensation and constant tension system, both motion and force control of the winch are important. This paper presents a digital displacement winch drive system and gives a description of challenges related to subsea lifting operations. The operation challenges are used to design a set of test cases for evaluating the performance of the digital displacement winch drive system.

• Donkov, Viktor Hristov; Andersen, Torben Ole; Ebbesen, Morten Kjeld; Linjama, Matti & Paloniitty, Miika (2019). Investigation of the fault tolerance of digital hydraulic cylinders. I Huhtala, Kalevi; Tikkanen, Seppo & Uusi-Heikkilä, Janne (Red.), The Sixteenth Scandinavian International Conference on Fluid Power, SICFP19: Proceedings. Tampere University of Technology. ISSN 978-952-03-1302-9. Vis sammendrag

  This paper investigates the fault tolerance of Discrete Displacement Cylinders (DDCs) controlled with a Model Predictive Controller(MPC). Due to the nature of DDCs there are multiple components such as several pressure chambers, constant pressure rails, and on/off valves, which operate in parallel. Some of these components do similar jobs, i.e. more than one cylinder chamber provides a positive force when pressurized. This modularity in design is an often stated benefit of digital hydraulics because failed components have less influence on the behaviour of the whole system. The exact influence of faults in the components, when the fault is detected and when it is not, is shown through a sensitivity study. Certain faults are tested in a laboratory setting to verify the simulation results. The results show that different component failures lead to different types of loss of capability of the system because the components are not equivalent in size. Furthermore the results show that the performance of the system is better when the fault is detected and the controller is able to take appropriate action.

• Nordås, Sondre; Beck, Michael M.; Ebbesen, Morten Kjeld & Andersen, Torben Ole (2019). Dynamic response of a digital displacement motor operating with various displacement strategies. Energies. ISSN 1996-1073. 12(9). doi: 10.3390/en12091737. Fulltekst i vitenarkiv Vis sammendrag

  Digital displacement technology has the potential of revolutionizing the performance of hydraulic piston pumps and motors. Instead of connecting each cylinder chamber to high and low pressure in conjunction with the shaft position, two electrically-controlled on/off valves are connected to each chamber. This allows for individual cylinder chamber control. Variable displacement can be achieved by using different displacement strategies, like for example the full stroke, partial stroke, or sequential partial stroke displacement strategy. Each displacement strategy has its transient and steady-state characteristics. This paper provides a detailed simulation analysis of the transient and steady-state response of a digital displacement motor running with various displacement strategies. The non-linear digital displacement motor model is verified by experimental work on a radial piston motor.

• Ketelsen, Søren; Padovani, Damiano; Andersen, Torben O.; Ebbesen, Morten Kjeld & Schmidt, Lasse (2019). Classification and review of pump-controlled differential cylinder drives. Energies. ISSN 1996-1073. 12:1293(7), s. 1–27. doi: 10.3390/en12071293. Fulltekst i vitenarkiv
• Donkov, Viktor Hristov; Andersen, Torben Ole; Pedersen, Henrik Clemmensen & Ebbesen, Morten Kjeld (2018). Application of Model Predictive Control in Discrete Displacement Cylinders to Drive a Knuckle Boom Crane, 2018 Global Fluid Power Society PhD Symposium (GFPS) . IEEE conference proceedings. ISSN 978-1-5386-4785-1. doi: 10.1109/GFPS.2018.8472363. Vis sammendrag

  In this paper, two Discrete Displacement Cylinders (DDCs) are used to drive the boom of a knuckle boom crane. DDCs operate by connecting one of several available pressure levels to each chamber in order to produce different forces. A trade-off exists with such systems, between the accuracy of tracking and energy dissipation due to switching. A popular way to approach this problem is a Force Shifting Algorithm (FSA). However, in this paper, the trade-off is managed by use of a Model Predictive Control (MPC) algorithm. The tracking accuracy and energy efficiency of the MPC and FSA strategies for DDCs are compared to a PID strategy for standard cylinders. The comparison is obtained by use of a computer simulation of a knuckle boom crane performing a realistic load cycle. The load cycle consists of the crane extending to pick up a load and then retracting to place it at an appropriate location. The main results show that MPC can deliver smoother and more accurate motion than FSA, while using less energy. Compared with standard cylinders and PID control, MPC uses less energy, but due to the switching of chamber pressures, the motion is smoother with the standard strategy. Both FSA and MPC can have degraded performance when a large change in load is introduced.

• Nordås, Sondre; Ebbesen, Morten Kjeld & Andersen, Torben Ole (2018). Analysis of requirements for valve accuracy and repeatability in high efficiency digital displacement motors, BATH/ASME 2018 Symposium on Fluid Power and Motion Control. The American Society of Mechanical Engineers (ASME). ISSN 978-0-7918-5196-8. doi: 10.1115/FPMC2018-8908.
• Hagen, Daniel; Padovani, Damiano & Ebbesen, Morten Kjeld (2018). Study of a Self-Contained Electro-Hydraulic Cylinder Drive, 2018 Global Fluid Power Society PhD Symposium (GFPS) . IEEE conference proceedings. ISSN 978-1-5386-4785-1. doi: 10.1109/GFPS.2018.8472360.
• Nordås, Sondre; Ebbesen, Morten Kjeld & Andersen, Toben Ole (2017). Feasibility Study of a Digital Hydraulic Winch Drive System, The Ninth Workshop on Digital Fluid Power. Aalborg Universitetsforlag. ISSN 9788792846754. doi: 10.1115/fpmc2019-1670.
• Donkov, Viktor Hristov; Andersen, Toben Ole; Ebbesen, Morten Kjeld & Pedersen, Henrik Clemmensen (2017). Applying Digital Hydraulic Technology on a Knuckle Boom Crane, The Ninth Workshop on Digital Fluid Power. Aalborg Universitetsforlag. ISSN 9788792846754.
• Nordås, Sondre; Ebbesen, Morten Kjeld & Andersen, Toben Ole (2017). The Potential of a Digital Hydraulic Winch Drive System, The Ninth Workshop on Digital Fluid Power. Aalborg Universitetsforlag. ISSN 9788792846754. Vis sammendrag

  This paper aims to evaluate the benefits and disadvantages of applying a digital hydraulic concept to actuate a knuckle boom crane. The standard cylinders of the knuckle boom crane will be substituted with multi-chamber cylinders of comparable size. The performance of one of the multi-chamber cylinders will be compared with the standard differential cylinder. The standard cylinder will be actuated with a constant pressure supply, a proportional directional valve and a proportional controller. Control performance and energy consumption for the two configurations have been considered. It is concluded that more research is needed into the control strategies in order to improve robustness and performance.

• Hagen, Daniel; Pawlus, Witold; Ebbesen, Morten Kjeld & Andersen, Torben Ole (2017). Feasibility Study of Electromechanical Cylinder Drivetrain for Offshore Mechatronic Systems. MIC Journal: Modeling, Identification and Control. ISSN 0332-7353. 38(2), s. 59–77. doi: 10.4173/mic.2017.2.2.
• 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.
• Sørensen, Jesper Kirk; Hansen, Michael Rygaard & Ebbesen, Morten Kjeld (2016). Numerical and experimental study of a novel concept for hydraulically controlled negative loads. MIC Journal: Modeling, Identification and Control. ISSN 0332-7353. 37(4), s. 195–211. doi: 10.4173/mic.2016.4.1.
• Sørensen, Jesper Kirk; Hansen, Michael Rygaard & Ebbesen, Morten Kjeld (2016). Novel concept for stabilising a hydraulic circuit containing counterbalance valve and pressure compensated flow supply. International Journal of Fluid Power. ISSN 1439-9776. 17(3), s. 153–162. doi: 10.1080/14399776.2016.1172446.
• Sørensen, Jesper Kirk; Hansen, Michael Rygaard & Ebbesen, Morten Kjeld (2015). Load independent velocity Control on boom motion using pressure Control valve. I Laamanen, Arto & Huhtala, Kalevi (Red.), The Fourteenth Scandinavian International Conference on Fluid Power, SICFP15. Proceedings. Tampere University of Technology. ISSN 978-952-15-3658-8. doi: 10.1115/fpni2014-7853.
• Langer, Thomas Heegaard; Ebbesen, Morten Kjeld & Kordestani, Ario (2015). Experimental analysis of occupational whole-body vibration exposure of agricultural tractor with large square baler. International Journal of Industrial Ergonomics. ISSN 0169-8141. 47, s. 79–83. doi: 10.1016/j.ergon.2015.02.009. Vis sammendrag

  This study investigates longitudinal whole-body vibration in agricultural tractors powering a large square baler. The aim is to test the hypothesis that four-wheel drive has an influence on the longitudinal dynamic response. A number of experimental measurements are carried out on a specific vehicle combination driving uphill and downhill. The whole-body vibration exposure is measured at the operator seat under different conditions. The statistic results show a significant difference on the whole-body vibration exposure depending on operating conditions. Driving uphill and downhill with four-wheel drive activated showed the highest difference with increased vibration level at downhill driving. The results indicate that four-wheel drive influences the longitudinal dynamics and hence the wholebody vibration exposure on tractors with large square balers. Relevance to industry: The findings of this work are highly relevant to the manufacturers of agricultural tractors and machinery as well advisers within occupational health. The paper demonstrates potential in reducing damaging vibrations by simple manual or automatic control of four-wheel drive.

• Sørensen, Jesper Kirk; Hansen, Michael Rygaard & Ebbesen, Morten Kjeld (2014). Boom Motion Control Using Pressure Control Valve, 8th FPNI Ph.D Symposium on Fluid Power, Proceedings. International symposium of product innovation management. ISSN 978-0-7918-4582-0. doi: 10.1115/FPNI2014-7853.
• Sørensen, Søren Emil; Hansen, Michael Rygaard; Ebbesen, Morten Kjeld & Mouritsen, Ole Østergaard (2013). Non-linear optimization of track layouts in loop-sorting-systems. Automation in Construction. ISSN 0926-5805. 31(3), s. 19–30. doi: 10.1016/j.autcon.2012.11.031. Vis sammendrag

  Optimization used for enhancing geometric structures is well known. Applying obstacles to the shape optimization problem is on the other hand not very common. It requires a fast contact search algorithm and an exact continuous formulation to solve the problem robustly. This paper focuses on combining shape optimization problems with collision avoidance constraints by which a collision detection algorithm is presented. The presented method is tested against the commercial loop-sorting-system used for sorting of medium sized items. The objective is to minimize price and footprint of the system while maintaining its functionality. Contact constraints are in this context important to include as various obstacles may surround the loop-sorting-system.

• Langer, Thomas; Iversen, Thorkil K.; Mouritsen, Ole Østergaard; Ebbesen, Morten Kjeld & Hansen, Michael Rygaard (2013). Suspension system performance optimization with discrete design variables. Structural And Multidisciplinary Optimization. ISSN 1615-147X. 47(4), s. 621–630. doi: 10.1007/s00158-013-0888-7. Vis sammendrag

  Suspension systems on commercial vehicles have become an important feature meeting the requirements from costumers and legislation. The performance of the suspension system is often limited by available catalogue components. Additionally the suspension performance is restricted by the travel speed which highly influences the ride comfort. In this article a suspension system for an articulated dump truck is optimized in sense of reducing elapsed time for two specified duty cycles without violating a certain comfort threshold level. The comfort threshold level is here defined as a whole-body vibration level calculated by ISO 2631-1. A three-dimensional multibody dynamics simulation model is applied to evaluate the suspension performance. A non-gradient optimization routine is used to find the best possible combination of continuous and discrete design variables including the optimum operational speed without violating a set of side constraints. The result shows that the comfort level converges to the comfort threshold level. Thus it is shown that the operational speed and hence the operator input influences the ride comfort level. Three catalogue components are identified by the optimization routine together with a set of continuous design variables and two operational speeds one for each load case. Thus the work demonstrates handling of human factors in optimization of a mechanical system with discrete and continuous design variables.

• Haastrup, Morten; Hansen, Michael Rygaard; Ebbesen, Morten Kjeld & Mouritsen, Ole Østergaard (2012). Modeling and Parameter Identification of Deflections in Planetary Stage of Wind Turbine Gearbox. MIC Journal: Modeling, Identification and Control. ISSN 0332-7353. 33(1), s. 1–11. doi: 10.4173/mic.2012.1.1. Vis sammendrag

  The main focus of this paper is the experimental and numerical investigation of a 750kW wind turbine gearbox. A detailed model of the gearbox with main shaft has been created using MSC.Adams. Special focus has been put on modeling the planet carrier (PLC) in the gearbox. For this purpose experimental data from a drive train test set up has been analyzed using parameter identification to quantify misalignments. Based on the measurements a combination of main shaft misalignment and planet carrier deflection has been identified. A purely numerical model has been developed and it shows good accordance with the experimental data.

• Sørensen, Søren Emil; Hansen, Michael Rygaard; Ebbesen, Morten Kjeld & Mouritsen, Ole Østergaard (2012). Enhanced chain dynamics in loop-sorting-systems by means of layout optimization and a kinematic model of the polygon action. Structural And Multidisciplinary Optimization. ISSN 1615-147X. 45(6), s. 907–916. doi: 10.1007/s00158-011-0743-7. Vis sammendrag

  Poor dynamics owing to polygon action is a known concern in mechanical applications of closed articulated chains. In this paper a kinematic model of the polygon action in large chains of loop-sorting-systems is proposed. Through optimization techniques the chain dynamics is improved by minimizing the polygon action using a parametric model of the track layout as design variables. Three formulations of the kinematic polygon action are tested on an average sized planer tracks layout to find a superior model. Verification of the proposed optimization method is performed using a state-of-the-art multi-body simulation model of the chain dynamics.

• Cibulka, Jaroslav; Ebbesen, Morten Kjeld & Robbersmyr, Kjell (2012). Bearing Fault Detection in Induction Motor-Gearbox Drivetrain. Journal of Physics: Conference Series (JPCS). ISSN 1742-6588. 364. doi: 10.1088/1742-6596/364/1/012140. Vis sammendrag

  The main contribution in the hereby presented paper is to investigate the fault detection capability of a motor current signature analysis by expanding its scope to include the gearbox, and not only the induction motor. Detecting bearing faults outside the induction motor through the stator current analysis represents an interesting alternative to traditional vibration analysis. Bearing faults cause changes in the stator current spectrum that can be used for fault diagnosis purposes. A time-domain simulation of the drivetrain model is developed. The drivetrain system consists of a loaded single stage gearbox driven by a line-fed induction motor. Three typical bearing faults in the gearbox are addressed, i.e. defects in the outer raceway, the inner raceway, and the rolling element. The interaction with the fault is modelled by means of kinematical and mechanical relations. The fault region is modelled in order to achieve gradual loss and gain of contact. A bearing fault generates an additional torque component that varies at the specific bearing defect frequency. The presented dynamic electromagnetic dq-model of an induction motor is adjusted for diagnostic purpose and considers such torque variations. The bearing fault is detected as a phase modulation of the stator current sine wave at the expected bearing defect frequency.

• 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.

• Sørensen, Søren Emil; Hansen, Michael Rygaard; Ebbesen, Morten Kjeld & Mouritsen, Ole Østergaard (2011). Implicit Identification of Contact Parameters in a Continuous Chain Model. MIC Journal: Modeling, Identification and Control. ISSN 0332-7353. 32(1), s. 1–15. doi: 10.4173/mic.2011.1.1. Vis sammendrag

  Accurate contact modeling is of great importance in the field of dynamic chain simulations. In this paper emphasis is on contact dynamics for a time-domain simulation model of large chains guided in a closed loop track. The chain model is based on theory for unconstrained rigid multibody dynamics where contact within the chain and with the track is defined through continuous point contacts using the contact indentation and rate as means. This paper presents an implicit method to determine contact parameters of the chain model through the use of none gradient optimization methods. The set of model parameters are estimated by minimizing the residual between simulated and measured results. The parameter identification is tested on four different formulations of the Hunt-Crossly hysteresis damping factor with the aim of recognizing a superior model.

• Sørensen, Søren Emil; Hansen, Michael Rygaard; Ebbesen, Morten Kjeld & Mouritsen, Ole Østergaard (2011). Time domain simulation of large-scale material handling chains using an unconstrained formulation. Proceedings of the Institution of mechanical engineers. Proceedings part K, journal of multi-body dynamics. ISSN 1464-4193. 225(2), s. 95–110. doi: 10.1177/1464419311406952. Vis sammendrag

  This article presents a dynamic time domain simulation model of loop-sortation systems. Loop-sortation systems for sortation of medium-size items are designed as a closed chain of carts guided in a closed loop track with a view to meet customers’ requirements of capacity and space available. Loop-sortation systems are complex mechatronic systems which require the use of simulation models in order to analyse, predict, and improve the dynamic performance in a cost efficient way. The model utilizes theory for unconstrained rigid multibody dynamics where contact between carts and between cart and track are modelled through the use of force elements. To determine contact between the track and the chain of carts, a rapid and robust contact search formulation has been developed and implemented in the model. Comparisons of main forces of the chain model are made with experimental measurements on three different test layouts. Verification results show that the normalized root mean square deviations are generally less than 10  percent.

• Haastrup, Morten; Hansen, Michael Rygaard & Ebbesen, Morten Kjeld (2011). Modeling of Wind Turbine Gearbox Mounting. MIC Journal: Modeling, Identification and Control. ISSN 0332-7353. 32(4), s. 141–149. doi: 10.4173/mic.2011.4.2. Vis sammendrag

  In this paper three bushing models are evaluated to find a best practice in modeling the mounting of wind turbine gearboxes. Parameter identification on measurements has been used to determine the bushing parameters for dynamic simulation of a gearbox including main shaft. The stiffness of the main components of the gearbox has been calculated. The torsional stiffness of the main shaft, gearbox and the mounting of the gearbox are of same order of magnitude, and eigenfrequency analysis clearly reveals that the stiffness of the gearbox mounting is of importance when modeling full wind turbine drivetrains.

• Ebbesen, Morten Kjeld & Hansen, Michael Rygaard (2011). Tool Point Control of Material Handling Crane in Marine Operations. 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. 1233–1241. Vis sammendrag

  In the current paper tool point control of hydraulically actuated manipulators is investigated. The considered application is a mobile loader crane. It is modeled as a planar mechanism with three degrees of freedom. In previous work a path planner has been developed that handles the redundancy by means of power consumption minimization while observing the different saturation phenomena associated with hydraulic actuation of mobile machinery. In this way a reference velocity is continuously computed and served to the controller that determines the optimal cylinder actuation. However, since one of the main competition parameters for mobile loader cranes is low weight it is clear that the deflection of the tool point caused by structural flexibility is something that cannot be ignored. In this paper this problem is handled by adding a correction procedure to the path planner that effectively reduces the trajectory error. The method calls for increased instrumentation in the shape of strain gauge measurements at a number of strategic points on the structure.

• Cibulka, Jaroslav; Ebbesen, Morten Kjeld & Robbersmyr, Kjell G (2011). Modeling of an Induction Motor-Gearbox Transmission with Respect to Condition Monitoring. 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. 808–816. Vis sammendrag

  Induction motors and gearboxes are used in many applications in the offshore oil industry. Faults in such drivetrains and especially in gearboxes lead to expensive downtime in the drilling or the production. A model of the Motor-Gearbox system addressing classical roller bearing damage is developed. The proposed model considers influence on the stator current from torque variations caused by bearing fault. In this paper it is shown that stator current monitoring is a possible technique for detecting faults in bearings outside the induction motor. In the present simulation model the torque variations due to the bearing fault are shown to cause periodic variations in the stator current. Detecting faults through current monitoring is expected to become an alternative to traditional vibration monitoring.

• Sørensen, Søren Emil; Hansen, Michael Rygaard & Ebbesen, Morten Kjeld (2010). An Experimentally Verified Model for Time Domain Simulation of Large Scale Material Handling Chains. I Klodowski, Adam (Red.), The First Joint International Conference on Multibody System Dynamics [Recurs electrònic] : Lappeenranta, Finland, May 25 - 27, 2010. Lappeenranta University of Technology. ISSN 9789522147783. Vis sammendrag

  A loop sorter system for sortation of medium size items is constructed as a closed chain of carts is running in a customer defined track. The complex mechatronic system makes the use of simulation models a vital tool in order to analyze and further improve the dynamic performance of the loop sorter. Theory in unconstrained rigid multibody dynamics is utilized to develop a time domain simulation model of the dynamics in the chain of carts. The contact between carts and between carts and track is modeled through the use of a penalty formulation. Two contact models of the wheel contacts are tested. A combination of analytic and numeric contact search algorithms is utilized to determine contact between the track and the wheels. Verification of the developed chain model is done by comparing experimental obtained data of forces in different contact points of the carts with corresponding data from conducted simulations. Data for the verification is obtained via a customized transducer cart on different loop sorter test layouts. The transducer cart is equipped to measure forces in all wheel contacts and forces in the links between the carts. Forces are measured for one lap on each test layout at the normal operation speed. Two different loop sorter layouts are used for verification of the presented multibody model. Accordance between measured and simulated data shows promising results. Forces in the joint between carts have a normal root mean square deviation that is less then 10%. Forces on the wheels also match the measured data well although the combination of static and impact contact makes it hard for the utilized contact models to compute forces correctly in both situations. Additional research on the wheel contact model may induce further improvements to the wheel contact forces.

• Ebbesen, Morten Kjeld & Hansen, Michael Rygaard (2010). Correction Scheme for Tool Point Velocity Control of a Flexible Hydraulically Actuated Manipulator. Proceedings of the IASTED International Conference on Modelling, Identification, and Control (MIC). ISSN 1025-8973. s. 298–305. Vis sammendrag

  In the current paper tool point control of hydraulically actuated manipulators is investigated. The considered application is a mobile loader crane. It is modeled as a planar mechanism with three degrees of freedom. In previous work a path planner has been developed that handles the redundancy by means of power consumption minimization while observing the different saturation phenomena associated with hydraulic actuation of mobile machinery. In this way a reference velocity is continuously computed and served to the controller that determines the optimal cylinder actuation. However, since one of the main competition parameters for mobile loader cranes is low weight it is clear that the deflection of the tool point caused by structural flexibility is something that cannot be ignored. In this paper this problem is handled by adding a correction procedure to the path planner that effectively reduces the trajectory error. The method utilizes only two of the three degrees of freedom and emphasis is on vertical adjustment and the simulation results show highly encouraging results. The method calls for increased instrumentation in the shape of strain gauge measurements at a number of strategic points on the structure.

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• Bhola, Mohit; Andersen, Torben Ole & Ebbesen, Morten Kjeld (2023). Design of Novel Closed-Circuit Hydrostatic Transmission without Charge Pump. Vis sammendrag

  This paper deals with the design of the control system for novel two-pumps one-motor (TPOM) systems for applications which require the deployment of a closed-circuit hydro-static transmission (HST). In conventional closed-circuit HST, the charge/booster pump is an integral part of the main pump used to compensate the leakages occurring in the circuit in order to maintain the lowest system pressure to avoid cavitation. The charge/booster pump in the closed-circuit HST is a source of constant power loss and increases heat load in the system. This reduces the efficiency of the transmission at part load operation. Also, the lowest system pressure in the conventional circuit is held constant by the relief valve deployed at the charge pump outlet. Hence, the stiffness of the system cannot be controlled based upon the transmission working condition. To overcome this limitation and enhancing transmission efficiency, the TPOM system is designed and evaluated without changing the basic functionality of the closed-circuit transmission. In TPOM, one of the displacement machines driven by permanent magnet synchronous motors (PMSM) works in open-circuit configuration and the other in closed-circuit configuration, without the need of a charge/booster pump. The TPOM is capable to operate in four-quadrants and capable to regenerate the energy during assistive load condition. This arrangement does not require the need of pilot pressure for varying the displacement of pump and motor, which generally is supplied by a booster/charge pump in a conventional closed-circuit transmission. However, innovative use of a hydraulic intensifier is proposed for the fulfilment of pilot pressure requirements. The feasibility in control shows the energy-saving potential of the HST without booster/charge pump.

• Mamo, Mebaye Belete; Ebbesen, Morten Kjeld & Poursina, Mohammad (2023). Dynamic Modelling and Simulation of Two-link Flexible Robot Using Rayleigh Beam Theory.
• Mamo, Mebaye Belete; Ebbesen, Morten Kjeld & Poursina, Mohammad (2023). Closed-Form Dynamic Model of Planar Multilink Flexible Manipulator.
• Zhao, Wei; Ebbesen, Morten Kjeld & Andersen, Torben Ole (2022). Identifying The Future Research Trend for Using Speed-Controlled Hydraulic Cylinders in Offshore Applications through Literature Survey.
• Nordås, Sondre; Ebbesen, Morten Kjeld & Andersen, Torben Ole (2019). Definition of Performance Requirements and Test Cases for Offshore/Subsea Winch Drive Systems With Digital Hydraulic Motors. Vis sammendrag

  A subsea crane is normally mounted on a floating vessel and equipped with a winch system. The crane can operate in water down to 3000 m. The vessel tends to move up and down due to waves. This heave motion makes offshore lifting operations challenging. In order to ease the winch operation in rough sea, the winch can be equipped with additional systems like active heave compensation and constant tension. In active heave compensation and constant tension system, both motion and force control of the winch are important. This paper presents a digital displacement winch drive system and gives a description of challenges related to subsea lifting operations. The operation challenges are used to design a set of test cases for evaluating the performance of the digital displacement winch drive system.

• Hagen, Daniel; Padovani, Damiano & Ebbesen, Morten Kjeld (2018). Study of a Self-Contained Electro-Hydraulic Cylinder Drive.
• Donkov, Viktor Hristov; Andersen, Torben Ole; Ebbesen, Morten Kjeld & Pedersen, Henrik clemmensen (2017). Applying Digital Hydraulic Technology on a Knuckle Boom Crane. Vis sammendrag

  This paper aims to evaluate the benefits and disadvantages of applying a digital hydraulic concept to actuate a knuckle boom crane. The standard cylinders of the knuckle boom crane will be substituted with multi-chamber cylinders of comparable size. The performance of one of the multi-chamber cylinders will be compared with the standard differential cylinder. The standard cylinder will be actuated with a constant pressure supply, a proportional directional valve and a proportional controller. Control performance and energy consumption for the two configurations have been considered. It is concluded that more research is needed into the control strategies in order to improve robustness and performance.

• Nordås, Sondre; Ebbesen, Morten Kjeld & Andersen, Torben Ole (2017). Feasibility Study of a Digital Hydraulic Winch Drive System. Vis sammendrag

  The offshore oil and gas industry has traditionally used hydraulically driven applications. Hydraulic systems are known to suffer from relatively low efficiency. Due to environmental issues, more efficient systems are now required. Today, the offshore oil and gas industry is experiencing a shift in driveline systems; high efficient electric motors tend to replace low efficient hydraulic systems. In addition to the electric motors, a new alternative to the conventional hydraulic system is digital hydraulic machines. This paper investigates the feasibility of using a digital hydraulic winch drive system and presents a new digital hydraulic winch drive control system. The simulated system is based on a 20000 kg hydraulic offshore auxiliary winch with a drum capacity of 3600 m of wire. The digital hydraulic winch drive system is a closed-circuit system with one high-speed digital pump and one low-speed high-torque digital motor. One of the biggest challenges in digital hydraulic pump/motor technology is the fast switching on/off valves. The valves must have high durability, low power consumption, zero leakage and low response time. The on/off valves in this study are modeled with an ideal behavior. The simulation results show that the payload follows the reference trajectory when using a digital hydraulic winch drive system for a wide range of loads and speeds.

• Nordås, Sondre; Ebbesen, Morten Kjeld & Torben Ole, Andersen (2017). The Potential of a Digital Hydraulic Winch Drive System. Vis sammendrag

  Digital hydraulic piston pumps and motors have shown the potential of improving efficiency in hydraulic systems. Two independently controlled fast switching on/off valves are connected to each piston chamber and allows for optimal valve timing and independent piston control. Each piston chamber is only pressurized when necessary, resulting in losses that almost scale with motor and pump displacement. This simulation study investigates the potential of using digital hydraulic pumps and motors to increase efficiency in a hydraulic offshore auxiliary winch with a safe working load equal to 20000 kg. One digital hydraulic winch drive system and one conventional hydraulic winch drive system are simulated hoisting two different loads. The payload in the first load case is 18000 kg and the payload in the second load case is 4000 kg. The efficiency and control performance of the two different winch drive systems are then evaluated. The simulation results show that digital hydraulic winch drive systems have the potential of increasing efficiency of hydraulic offshore winches.

• Ebbesen, Morten Kjeld (2016). Mekatronikkstudiet på UiA.
• 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.
• Ebbesen, Morten Kjeld (2015). Mekatronikkstudiet på UiA og laboratorieaktiviteter.
• Ebbesen, Morten Kjeld (2015). Mekatronikkstudiet på UiA.
• Ebbesen, Morten Kjeld (2014). Opposisjonsinnlegg ved Behnam Ghalamchis doktordisputas på Lappeenranta University of Technology (LUT), Finland i forbindelse med forsvaret av avhandlingen "Dynamic Analysis Model of Spherical Roller Bearings with Defects".
• Ebbesen, Morten Kjeld (2014). Mekatronikkstudiet på UiA.
• Ebbesen, Morten Kjeld (2013). Mekatronikkstudiet på UiA.
• Ebbesen, Morten Kjeld (2012). Mekatronikk på UiA.
• Ebbesen, Morten Kjeld (2012). Mekatronikkstudiet på UiA for Mandal videregående skole.
• Ebbesen, Morten Kjeld (2012). Mekatronikkstudiet på UiA.
• Sørensen, Søren Emil; Ebbesen, Morten Kjeld & Mouritsen, Ole Østergaard (2009). An Improved Multibody Model of Closed Chains in Loop-sorter-systems An Improved Multibody Model of Closed Chains in Loop-sorter-systems, Proceedings of the Twenty Second Nordic Seminar on computational Mechanics. Aalborg Universitetsforlag. Vis sammendrag

  An improved formulation for simulation of closed chains in loop-sorter-systems is presented. Previous models have shown that reasonable results can be reached using rigid multibody dynamic. The improvements done to the model has been aimed on increased accuracy, reduced evaluation time and improved pre and post processing of simulation data. The evaluation time is reduced significantly although the presented results show only minor improvements to the accuracy.

• Donkov, Viktor Hristov; Andersen, Torben Ole & Ebbesen, Morten Kjeld (2020). Secondary Control of Multi-chamber Cylinders for Low-speed, High-force, Offshore Applications. Aalborg Universitetsforlag. ISSN 978-87-7210-810-0. Vis sammendrag

  The ongoing global warming crisis and the increasing cost of energy demand improvements in many industries. Technologies and methods, which were once sufficient, must again and again be examined and improved. One of these technologies is hydraulic actuation. Hydraulic systems may have efficiencies as low as 30 %. Due to their many benefits such inefficiencies have been disregarded to some extent. In recent years both academia and industry have put a higher focus on efficiency, and different paradigm shifts are being investigated. Digital hydraulics is one such paradigm, which relies on the notion that a component, which is switched off, does not incur losses, while one that is used to its maximum potential can be designed to be efficient for that operation condition. Multi-chamber cylinders are a part of the digital hydraulics field. They are hydraulic cylinders, which have more than two chambers. Each chamber has a different cross-sectional area. Different forces can be generated by connecting the chambers to different predefined pressures. This concept removes the need for proportional control valves and throttling. Removing throttling removes a major part of the losses in hydraulic systems. When a system is controlled in such a way as to only extract the necessary energy from a source, without changing the sources output, it is called secondary control. One of the challenges in implementing secondary controlled multi-chamber cylinders is that the hydraulic cylinder in such a solution is more complex than a standard hydraulic cylinder. Very limited research has been conducted, documenting the performance of digitally controlled cylinders on low-speed, high-force applications. Concerns about the smoothness of motion, the possibility of pressure spikes, and the computational complexity of the control structure have been raised. This thesis addresses these difficulties. First it investigates the performance of a multi-chamber cylinder in a low-speed, high-force application such as a knuckle boom crane. It is shown that while simpler control structures can get the job done, a more complicated structure such as Model Predictive Control (MPC) can give better performance. The optimization problem inherent in MPC, the controllers sensitivity, and the controllers robustness are also studied. In trying to study the smoothness of motion of a cylinder, the project faced a lack of tools with which to measure it and the use of total harmonic distortion, a concept from electrical engineering is proposed. The project concludes that multi-chamber cylinders can have smooth, energy efficient motion if MPC with integral action is used and certain conditions are met - mostly known or selected system parameters. When changes are introduced the energy efficiency suffers first followed by smoothness of motion. The project also concludes that when MPC is used for position control, a short time horizon can be sufficient. In this case a much simpler optimization method can still give good results. In this case MPC works more like model based control. Overall, multi-chamber cylinders are an intriguing solution, but more research into making their performance more robust is needed before they can find wider popularity.

• Nordås, Sondre; Ebbesen, Morten Kjeld & Andersen, Torben Ole (2020). Using Digital Hydraulics in Secondary Control of Motor Drive. Wittusen & Jensen. ISSN 978-82-7117-966-3. Fulltekst i vitenarkiv

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