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  • 1.
    Freidovich, Leonid B.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    La Hera, Pedro M.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Mettin, Uwe
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Robertsson, Anders
    Department of Automatic Control, LTH, Lund University.
    Shiriaev, Anton
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Johansson, Rolf
    Department of Automatic Control, LTH, Lund University.
    Shaping stable periodic motions of inertia wheel pendulum: theory and experiment2009In: Asian journal of control, ISSN 1561-8625, E-ISSN 1561-8625, Vol. 11, no 5, p. 549-556Article in journal (Refereed)
    Abstract [en]

    We consider an underactuated two-link robot called the inertia wheel pendulum. The system consists of a free planar rotational pendulum and a symmetric disk attached to its end, which is directly controlled by a DC-motor. The goal is to create stable oscillations of the pendulum, which is not directly actuated. We exploit a recently proposed feedback-control design strategy based on motion planning via virtual holonomic constraints. This strategy is shown to be useful for design of regulators for achieving orbitally exponentially stable oscillatory motions. The main contribution is a step-by-step procedure on how to achieve oscillations with pre-specified amplitude from a given range and an arbitrary independently chosen period. The theoretical results are verified via experiments with a real hardware setup.

  • 2.
    Khan, Muhammad Sikandar Lal
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    ur Réhman, Shafiq
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    La Hera, Pedro
    Liu, Feng
    Li, Haibo
    A pilot user's prospective in mobile robotic telepresence system2014In: 2014 Asia-Pacific Signal and Information Processing Association Annual Summit and Conference (APSIPA 2014), IEEE, 2014Conference paper (Refereed)
    Abstract [en]

    In this work we present an interactive video conferencing system specifically designed for enhancing the experience of video teleconferencing for a pilot user. We have used an Embodied Telepresence System (ETS) which was previously designed to enhance the experience of video teleconferencing for the collaborators. In this work we have deployed an ETS in a novel scenario to improve the experience of pilot user during distance communication. The ETS is used to adjust the view of the pilot user at the distance location (e.g. distance located conference/meeting). The velocity profile control for the ETS is developed which is implicitly controlled by the head of the pilot user. The experiment was conducted to test whether the view adjustment capability of an ETS increases the collaboration experience of video conferencing for the pilot user or not. The user study was conducted in which participants (pilot users) performed interaction using ETS and with traditional computer based video conferencing tool. Overall, the user study suggests the effectiveness of our approach and hence results in enhancing the experience of video conferencing for the pilot user.

  • 3.
    La Hera, Pedro
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Traversing from Point-to-Point along a straight line with a ballbot2010In: 8th IFAC Symposium on Nonlinear Control Systems, 2010Conference paper (Refereed)
  • 4.
    La Hera, Pedro
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Underactuated mechanical systems: Contributions to trajectory planning, analysis, and control2011Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Nature and its variety of motion forms have inspired new robot designs with inherentunderactuated dynamics. The fundamental characteristic of these controlled mechanicalsystems, called underactuated, is to have the number of actuators less than the number ofdegrees of freedom. The absence of full actuation brings challenges to planning feasibletrajectories and designing controllers. This is in contrast to classical fully-actuated robots.A particular problem that arises upon study of such systems is that of generating periodicmotions, which can be seen in various natural actions such as walking, running,hopping, dribbling a ball, etc. It is assumed that dynamics can be modeled by a classicalset of second-order nonlinear differential equations with impulse effects describing possibleinstantaneous impacts, such as the collision of the foot with the ground at heel strikein a walking gait. Hence, we arrive at creating periodic solutions in underactuated Euler-Lagrange systems with or without impulse effects. However, in the qualitative theory ofnonlinear dynamical systems, the problem of verifying existence of periodic trajectoriesis a rather nontrivial subject.The aim of this work is to propose systematic procedures to plan such motions and ananalytical technique to design orbitally stabilizing feedback controllers. We analyze andexemplify both cases, when the robotmodel is described just by continuous dynamics, andwhen continuous dynamics is interrupted from time to time by state-dependent updates.For trajectory planning, systems with one or two passive links are considered, forwhich conditions are derived to achieve periodicmotions by encoding synchronizedmovementsof all the degrees of freedom. For controller design we use an explicit form tolinearize dynamics transverse to the motion. This computation is valid for an arbitrarydegree of under-actuation. The linear system obtained, called transverse linearization, isused to analyze local properties in a vicinity of the motion, and also to design feedbackcontrollers. The theoretical background of these methods is presented, and developedin detail for some particular examples. They include the generation of oscillations forinverted pendulums, the analysis of human movements by captured motion data, and asystematic gait synthesis approach for a three-link biped walker with one actuator.

  • 5.
    La Hera, Pedro
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Freidovich, Leonid
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Shiriaev, Anton
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Mettin, Uwe
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    New approach for swinging up the Furuta pendulum: theory and experiments2009In: Mechatronics (Oxford), ISSN 0957-4158, E-ISSN 1873-4006, Vol. 19, no 8, p. 1240-1250Article in journal (Refereed)
    Abstract [en]

    The problem of swinging up inverted pendulums has often been solved by stabilizing a particular class of homoclinic structures present in the dynamics of a physical pendulum. Here, new arguments are suggested to show how other homoclinic curves can be preplanned for dynamics of the passive-link of the robot. This is done by reparameterizing the motions according to geometrical relations among the generalized coordinates, which are known as virtual holonomic constraints. After that, conditions that guarantee the existence of periodic solutions surrounding the planned homoclinic orbits are derived. The corresponding trajectories, in contrast to homoclinic curves, admit efficient design of feedback control laws ensuring exponential orbital stabilization. The method is illustrated by simulations and supported by experimental studies on the Furuta pendulum. The implementation issues are discussed in detail.

  • 6.
    La Hera, Pedro M
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Mettin, Uwe
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Westerberg, Simon
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Shiriaev, Anton S
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Modeling and control of hydraulic rotary actuators used in forestry cranes2009In: ICRA: 2009 IEEE international conference on robotics and automation, vols 1-7, 2009, p. 2161-2166Conference paper (Refereed)
    Abstract [en]

    The steps for modeling and control of a hydraulic rotary actuator are discussed. Our aim is to present experimental results working with a particular sensing device for angular position as a complement to pressure sensing devices. We provide the steps in experimental system identification used for modeling the system dynamics. The cascade controller designed contains an inner loop for an accurate tracking of torque while stabilizing position reference trajectories. The performance of this design is experimentally verified.

  • 7.
    La Hera, Pedro M.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Shiriaev, Anton S.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Freidovich, Leonid B.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Mettin, Uwe
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Gait synthesis for a three-link planar biped walker with one actuator2010In: IEEE International Conference on Robotics and Automation (ICRA), 2010, 2010, p. 1715-1720Conference paper (Refereed)
    Abstract [en]

    We consider a 3-link planar walker with two legs and an upper body. An actuator is introduced between the legs, and the torso is kept upright by torsional springs. The model is a 3-DOF impulsive mechanical system, and the aim is to induce stable limit-cycle walking in level ground. To solve the problem, the ideas of the virtual holonomic constraints approach are explored, used and extended. The contribution is a novel systematic motion planning procedure for solving the problem of gait synthesis, which is challenging for non-feedback linearizable mechanical systems with two or more passive degrees of freedom. For a preplanned gait we compute an impulsive linear system that approximates dynamics transversal to the periodic solution. This linear system is used for the design of a stabilizing feedback controller. Results of numerical simulations are presented to illustrate the performance of the closed loop system.

  • 8.
    La Hera, Pedro M.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Shiriaev, Anton S.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Freidovich, Leonid B.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Mettin, Uwe
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Orbital stabilization of a pre-planned periodic motion to swing up the Furuta pendulum: theory and experiments2009In: ICRA: 2009 IEEE International conference in robotics an automation, 7 vol., 2009, p. 3562-3567Conference paper (Refereed)
    Abstract [en]

    The problem of swinging up inverted pendulums has often been solved by stabilization of a particular class of homoclinic structures present in the dynamics of the standard pendulum. In this article new arguments are suggested to show how different homoclinic curves can be preplanned for dynamics of the passive-link of the robot. This is done by reparameterizing the motion according to geometrical relations among the generalized coordinates. It is also shown that under certain conditions there exist periodic solutions surrounding such homoclinic orbits. These trajectories admit designing feedback controllers to ensure exponential orbital stabilization. The method is illustrated by simulations and supported by experimental studies.

  • 9.
    La Hera, Pedro
    et al.
    Umeå University, Faculty of Science and Technology, Applied Physics and Electronics.
    Mettin, Uwe
    Umeå University, Faculty of Science and Technology, Applied Physics and Electronics.
    Manchester, Ian
    Computer Science and Artificial Intelligence Lab, Massachusetts Institute of Technology, Cambridge MA, 02139, USA.
    Shiriaev, Anton
    Umeå University, Faculty of Science and Technology, Applied Physics and Electronics.
    Identification and control of a hydraulic forestry crane2008In: Proceedings of the 17th IFAC World Congress: COEX, South Korea, Elsevier , 2008, p. 2306-2311Conference paper (Refereed)
    Abstract [en]

    This article presents the identification and control of an electro-hydraulic crane. The crane is of the type used on forestry vehicles known as forwarders, which travel off-road collecting logs cut by the harvesters. The dynamics identified include significant frictional forces, dead zones, and structural and hydraulic vibrations. The control algorithm proposed, comprised of a linear controller and a compensator for nonlinearities, is able to accurately track a reference trajectory for the end effector, despite uncertainties in the arm mechanics and hydraulic system dynamics. A further control design is presented which uses an inner loop to compensate for vibrations in the hydraulic system, and its performance is experimentally verified.

  • 10. La Hera, Pedro
    et al.
    Morales, Daniel Ortiz
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Model-Based Development of Control Systems for Forestry Cranes2015In: Journal of Control Science and Engineering, ISSN 1687-5249, E-ISSN 1687-5257, Vol. 2015, article id 256951Article in journal (Refereed)
    Abstract [en]

    Model-based methods are used in industry for prototyping concepts based on mathematical models. With our forest industry partners, we have established a model-based workflow for rapid development of motion control systems for forestry cranes. Applying this working method, we can verify control algorithms, both theoretically and practically. This paper is an example of this workflow and presents four topics related to the application of nonlinear control theory. The first topic presents the system of differential equations describing the motion dynamics. The second topic presents nonlinear control laws formulated according to sliding mode control theory. The third topic presents a procedure for model calibration and control tuning that are a prerequisite to realize experimental tests. The fourth topic presents the results of tests performed on an experimental crane specifically equipped for these tasks. Results of these studies show the advantages and disadvantages of these control algorithms, and they highlight their performance in terms of robustness and smoothness.

  • 11.
    La Hera, Pedro
    et al.
    Sveriges lantbruksuniversitet .
    Ortiz Morales, Daniel
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Designing and testing control systems for forestry cranesManuscript (preprint) (Other academic)
    Abstract [en]

    Motivated by the interest, and in collaboration of forestry machine manufacturers, a number of motion control algorithms have been designed, implemented, and tested in a forwarder crane. The aim has been to achieve the robust tracking of reference link motion trajectories based on sensory feedback coming from pressure and angular displacement sensors mounted in the manipulator. To this end, a procedure employing computer aided model-based methods and simulation technology have been suggested, in order to produce systematical tools for model analysis, tuning of controllers, and rapid prototyping for hardware-in-the-loop testing. The controllers derived have the objective to form the background of a new generation of crane control modes, which will be subsequently designed by the use of different motion planning techniques. We present results of experimental studies carried out on a medium-size crane, which has been properly equipped for the task of rapid-prototyping.

  • 12.
    La Hera, Pedro
    et al.
    Sveriges lantbruksuniversitet .
    Ortiz Morales, Daniel
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Non-linear dynamics modelling description for simulating the behavior of forestry cranes2014In: International journal of Modeling, identification and control, ISSN 1746-6172, E-ISSN 1746-6180, Vol. 21, no 2, p. 125-138Article in journal (Refereed)
    Abstract [en]

    Model-based design is a standard framework widely adopted in modern industry. It is used for designing multi-domain engineering solutions based on computer-aided simulation technology. Currently, this approach is also being viewed as a tentative method for designing modern heavy-duty machine technology. Under this motivation, our aim is to present how modeling techniques can be used for simulating dynamics of forestry machines. To this end, we consider a forestry crane, and propose mathematical models and calibration techniques, such that model-based methods can subsequently be applied. The complexity of the machine is represented by first principle laws, in which the mechanical system is modeled by Euler-Lagrange formulations, and the hydraulic system is modeled by principles of fluid dynamics. The calibration algorithms are performed by statistical algorithms based on linear and nonlinear least-squares methods. The results of simulation show a significant correspondence between the simulated and observed variables, validating our procedures.

  • 13.
    La Hera, Pedro
    et al.
    Swedish University of Agricultural Sciences, Umeå, Sweden.
    Rehman, Bilal Ur
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Morales, Daniel Ortiz
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Electro-hydraulically actuated forestry manipulator: Modeling and Identification2012In: 2012 IEEE/RSJ Iinternational Conference on Intelligent Robots and Systems (IROS), New York: IEEE conference proceedings, 2012, p. 3399-3404Conference paper (Refereed)
    Abstract [en]

    We present results of modeling dynamics of a forestry manipulator, in which we consider its mechanics, as well as its hydraulic actuation system. The mathematical model of its mechanics is formulated by Euler-Lagrange equations, for which the addition of friction forces is straightforward. Dynamics of the hydraulic system is modeled upon first principle laws, which concern flow through orifices and fluid compressibility. These models lead to a set of equations with various unknown parameters, which are related to the inertias, masses, location of center of masses, friction forces, and valve coefficients. The numerical values of these parameters are estimated by the use of least-square methods, which is made feasible by transforming the models into linear representations. The results of simulation tests show a significant correspondence between measured and estimated variables, validating our modeling and identification approach.

  • 14.
    La Hera, Pedro
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics. SLU, Dept Forestry Technol, Umeå, Sweden and Swedish Cluster Forest Technol, Vindeln, Sweden.
    Shiriaev, Anton S.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics. Norwegian Univ Sci & Technol, Dept Engn Cybernet, Trondheim, Norway.
    Freidovich, Leonid B
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Mettin, Uwe
    Gusev, Sergey V.
    Stable walking gaits for a three-link planar biped robot with one actuator2013In: IEEE Transactions on robotics, ISSN 1552-3098, E-ISSN 1941-0468, IEEE transactions on robotics, Vol. 29, no 3, p. 589-601Article in journal (Refereed)
    Abstract [en]

    We consider a benchmark example of a three-link planar biped walker with torso, which is actuated in between the legs. The torso is thought to be kept upright by two identical torsional springs. The mathematical model reflects a three-degree-of-freedom mechanical system with impulse effects, which describe the impacts of the swing leg with the ground, and the aim is to induce stable limit-cycle walking on level ground. The main contribution is a novel systematic trajectory planning procedure for solving the problem of gait synthesis. The key idea is to find a system of ordinary differential equations for the functions describing a synchronization pattern for the time evolution of the generalized coordinates along a periodic motion. These functions, which are known as virtual holonomic constraints, are also used to compute an impulsive linear system that approximates the time evolution of the subset of coordinates that are transverse to the orbit of the continuous part of the periodic solution. This auxiliary system, which is known as transverse linearization, is used to design a nonlinear exponentially orbitally stabilizing feedback controller. The performance of the closed-loop system and its robustness with respect to various perturbations and uncertainties are illustrated via numerical simulations.

  • 15.
    La Hera, Pedro X
    et al.
    Swedish University of Agricultural Sciences.
    Ortíz Morales, Daniel
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Modeling dynamics of an electro-hydraulic servo actuated manipulator: A case study of a forestry forwarder crane2012In: World Automation Congress (WAC), 2012, 2012Conference paper (Refereed)
    Abstract [en]

    System modeling and parameters estimation are key elements to realize model-based control. Here, we present a discussion of modeling dynamics of a forestry forwarder crane, for which standard Euler-Lagrange formulations are used to describe its equations of motion. To calibrate this model according to experimental data, we perform parameter estimation based on the method of least squares. This procedure allows identifying various unknown parameters, which are related to the inertias, masses, location of center of masses, and friction forces coefficients. The results of simulation tests show a significant correspondence between measured and estimated variables, validating our modeling approach.

  • 16.
    Lindroos, Ola
    et al.
    SLU.
    Ringdahl, Ola
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Pedro, La Hera
    SLU.
    Hohnloser, Peter
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Hellström, Thomas
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Estimating the position of the harvester head: a key step towards the precision forestry of the future?2015In: Croatian Journal of Forest Engineering, ISSN 1845-5719, E-ISSN 1848-9672, Vol. 36, no 2, p. 147-164Article in journal (Refereed)
    Abstract [en]

    Modern harvesters are technologically sophisticated, with many useful features such as the ability to automatically measure stem diameters and lengths. This information is processed in real time to support value optimization when cutting stems into logs. It can also be transferred from the harvesters to centralized systems and used for wood supply management. Such information management systems have been available since the 1990s in Sweden and Finland, and are constantly being upgraded. However, data on the position of the harvester head relative to the machine are generally not recorded during harvesting. The routine acquisition and analysis of such data could offer several opportunities to improve forestry operations and related processes in the future. Here, we analyze the possible benefits of having this information, as well as the steps required to collect and process it. The benefits and drawbacks of different sensing technologies are discussed in terms of potential applications, accuracy and cost. We also present the results of preliminary testing using two of the proposed methods. Our analysis indicates that an improved scope for mapping and controlling machine movement is the main benefit that is directly related to the conduct of forestry operations. In addition, there are important indirect benefits relating to ecological mapping. Our analysis suggests that both of these benefits can be realized by measuring the angles of crane joints or the locations of crane segments and using the resulting information to compute the head's position. In keeping with our findings, two companies have recently introduced sensor equipped crane solutions.

  • 17.
    Mettin, Uwe
    et al.
    Department of Engineering Cybernetics, Norwegian University of Science and Technology.
    La Hera, Pedro
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Freidovich, Leonid
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Shiriaev, Anton
    Department of Engineering Cybernetics, Norwegian University of Science and Technology.
    How Springs Can Help to Stabilize Motions of Underactuated Systems with Weak Actuators2008Conference paper (Refereed)
    Abstract [en]

    In the field of robotics the energy spent for actuation is always an issue. It is often the case that some desired motions cannot be achieved by the robot due to limitations in actuation power. We suggest a simple solution to the problem: complement the actuators by some configuration of mechanical springs which delivers a torque profile that is well-tuned for the desired robot motion. As a result, the control effort for the original actuator will be reduced. In this case study we consider an underactuated planar two-link robot for experimental demonstration of the concept. The virtual holonomic constraints approach serves as analytical tool to parameterize, plan, and stabilize desired periodic motions.

  • 18.
    Mettin, Uwe
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    La Hera, Pedro M.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Freidovich, Leonid B.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Shiriaev, Anton
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Generating human-like motions for an underactuated three-link robot based on the virtual constraints approach2007In: Proceedings of the 46th IEEE conference on decision and control, 2007, p. 5138-5143Conference paper (Refereed)
    Abstract [en]

    In the field of robotics there is a great interest in developing strategies and algorithms to reproduce human-like behavior. In this paper, we consider motion planning and generation for humanoid robots based on the concept of virtual holonomic constraints. For this purpose, recorded kinematic data from a particular human motion are analyzed in order to extract geometric relations among various joint angles defining the instantaneous postures. The analysis of a simplified human body representation leads to dynamics of a corresponding underactuated mechanical system with parameters based on anthropometric data of an average person. The motion planning is realized by considering solutions of reduced system dynamics assuming the virtual holonomic constraints are kept invariant The relevance of such a mathematical model in accordance to the real human motion under study is shown. An appropriate controller design procedure is presented together with simulation results of a feedback-controlled robot.

  • 19.
    Mettin, Uwe
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    La Hera, Pedro M.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Freidovich, Leonid
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Shiriaev, Anton
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Helbo, Jan
    Aalborg university, Denmark.
    Motion planning for humanoid robots based on virtual constraints extracted from recorded human movements2008In: Intelligent Service Robotics, ISSN 1861-2776, Vol. 1, no 4, p. 289-301Article in journal (Refereed)
    Abstract [en]

    In the field of robotics there is a great interest in developing strategies and algorithms to reproduce human-like behavior. In this paper, we consider motion planning for humanoid robots based on the concept of virtual holonomic constraints. At first, recorded kinematic data of particular human motions are analyzed in order to extract consistent geometric relations among various joint angles defining the instantaneous postures. Second, a simplified human body representation leads to dynamics of an underactuated mechanical system with parameters based on anthropometric data. Motion planning for humanoid robots of similar structure can be carried out by considering solutions of reduced dynamics obtained by imposing the virtual holonomic constraints that are found in human movements. The relevance of such a reduced mathematical model in accordance with the real human motions under study is shown. Since the virtual constraints must be imposed on the robot dynamics by feedback control, the design procedure for a suitable controller is briefly discussed.

  • 20.
    Mettin, Uwe
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    La Hera, Pedro
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Shiriaev, Anton
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Freidovich, Leonid
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Reducing control efforts for preplanned motions by parallel elastic actuators2010In: The international journal of robotics research, ISSN 0278-3649, E-ISSN 1741-3176, Vol. 29, no 9, p. 1186-1198Article in journal (Refereed)
    Abstract [en]

    A lack of sufficient actuation power as well as the presence of passive degrees of freedom are often serious constraints for feasible motions of a robot. Installing passive elastic mechanisms in parallel with the original actuators is one of a few alternatives that allows for large modifications of the range of external forces or torques that can be applied to the mechanical system. If some motions are planned that require a nominal control input above the actuator limitations, then we can search for auxiliary spring-like mechanisms complementing the control scheme in order to overcome the constraints. The intuitive idea of parallel elastic actuation is that spring-like elements generate most of the nominal torque required along a desired trajectory, so the control efforts of the original actuators can be mainly spent in stabilizing the motion. Such attractive arguments are, however, challenging for robots with non-feedback linearizable non-minimum phase dynamics that have one or several passive degrees of freedom. We suggest an approach to resolve the apparent difficulties and illustrate the method with an example of an underactuated planar double pendulum. The results are tested both in simulations and through experimental studies.

  • 21.
    Mettin, Uwe
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    La Hera, Pedro X.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Freidovich, Leonid B.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Shiriaev, Anton S.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Parallel elastic actuators as a control tool for preplanned trajectories of underactuated mechanical systems2009In: The international journal of robotics research, ISSN 0278-3649, E-ISSN 1741-3176, Vol. 29, no 9, p. 1186-1198Article in journal (Refereed)
    Abstract [en]

    A lack of sufficient actuation power as well as the presence of passive degrees of freedom are often serious constraints for feasible motions of a robot. Installing passive elastic mechanisms in parallel with the original actuators is one of a few alternatives that allows for large modifications of the range of external forces or torques that can be applied to the mechanical system. If some motions are planned that require a nominal control input above the actuator limitations, then we can search for auxiliary spring-like mechanisms complementing the control scheme in order to overcome the constraints. The intuitive idea of parallel elastic actuation is that spring-like elements generate most of the nominal torque required along a desired trajectory, so the control efforts of the original actuators can be mainly spent in stabilizing the motion. Such attractive arguments are, however, challenging for robots with non-feedback linearizable non-minimum phase dynamics that have one or several passive degrees of freedom. We suggest an approach to resolve the apparent difficulties and illustrate the method with an example of an underactuated planar double pendulum. The results are tested both in simulations and through experimental studies.

  • 22.
    Mettin, Uwe
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    La Hera, Pedro X.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Ortiz Morales, Daniel
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Shiriaev, Anton
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Freidovich, Leonid
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Westerberg, Simon
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Trajectory planning and time-independent motion control for a kinematically redundant hydraulic manipulator2009In: Advanced Robotics, 2009. ICAR 2009. International Conference on, IEEE conference proceedings, 2009, p. 1-6Conference paper (Refereed)
    Abstract [en]

    In this paper we consider the problem of motion planning and control of a kinematically redundant manipulator, which is used on forestry machines for logging. Once a desired path is specified in the 3D world frame, a trajectory can be planned and executed such that all joints are synchronized and constrained to the Cartesian path. We introduce an optimization procedure that takes advantage of the kinematic redundancy so that time-efficient joint and velocity profiles along the path can be obtained. Differential constraints imposed by the manipulator dynamics are accounted for by employing a phase-plane technique for admissible path timings. In hydraulic manipulators, such as considered here, the velocity constraints of the individual joints are particularly restrictive. We suggest a time-independent control scheme for the planned trajectory which is built upon the standard reference tracking controllers. Experimental tests underline the benefits and efficiency of the model-based trajectory planning and show success of the proposed control strategy.

  • 23.
    Mettin, Uwe
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Westerberg, Simon
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Shiriaev, Anton
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    La Hera, Pedro X.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Analysis of human-operated motions and trajectory replanning for kinematically redundant manipulators2009In: 2009 IEEE/RSJ International Conference on Intelligent Robots and Systems: St.Louis, USA, 2009, p. 795-800Conference paper (Refereed)
    Abstract [en]

    We consider trajectory planning for kinematically redundant manipulators used on forestry machines. The analysis of recorded data from human operation reveals that the driver does not use the full potential of the machine due to the complexity of the manipulation task. We suggest an optimization procedure that takes advantage of the kinematic redundancy so that time-efficient joint and velocity profiles along the path can be obtained. Differential constraints imposed by the manipulator dynamics are accounted for by employing a phase-plane technique for admissible path timings. Velocity constraints of the individual joints are particularly restrictive in hydraulic manipulators. Our study aims for semi-autonomous schemes that can provide assistance to the operator for executing global motions.

  • 24.
    Miranda La Hera, Pedro
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Rehman, Bilal Ur
    Sandberg, Anders
    Modeling an industrial flotation process: A case study at the mining company Boliden AB2012In: 2012 WORLD AUTOMATION CONGRESS (WAC), IEEE , 2012, p. 1-5Conference paper (Refereed)
    Abstract [en]

    We present results of modeling dynamics of a copper flotation pl'ocess, for which conventional system identification methods are applied. To this end, experimental studies are performed at an open pit mine belonging to the Swedish mining company Boliden AB. The main idea is to identify linear plants, that approximate dynamics of the process around neighborhoods of cost efficient working conditions. These models are intended to be applied for the design of model based control strategies, and to assess better studies of performance optimization. The results of simulation tests show a satisfactory agreement in between the identified models performance and the measured variables.

  • 25.
    Miranda La Hera, Pedro Xavier
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Contributions to motion planning and orbital stabilization: case studies: Furuta pendulum swing up, inertia wheel oscillations and biped robot walking2008Licentiate thesis, monograph (Other academic)
    Abstract [en]

    Generating and stabilizing periodic motions in nonlinear systems is a challenging task. In the control system community this topic is also known as limit cycle control. In recent years a framework known as Virtual Holonomic Constraints (VHC) has been developed as one of the solutions to this problem. The aim of this thesis is to give an insight into this approach and its practical application.

    The contribution of this work is primarily the experimental validation of the theory. A step by step procedure of this methodology is given for motion planning, as well as for controller design. Three particular setups were chosen for experiments: the inertia wheel pendulum, the Furuta pendulum and the two-link planar pendulum. These under-actuated mechanical systems are well known benchmarking setups for testing advanced control design methods.

    Further application is intended for cases such as biped robot walking/running, human and animal locomotion analysis, etc.

  • 26.
    Ortiz Morales, Daniel
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    La Hera, Pedro
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Mettin, Uwe
    Department of Engineering Cybernetics, Norwegian University of Science and Technology.
    Freidovich, Leonid
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Shiriaev, Anton
    Department of Engineering Cybernetics, Norwegian University of Science and Technology.
    Westerberg, Simon
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Steps in trajectory planning and controller design for a hydraulically driven crane with limited sensing2010In: IEEE International Conference on Intelligent Robots and Systems, IEEE conference proceedings, 2010, p. 3836-3841Conference paper (Refereed)
    Abstract [en]

    In the forest industry, trees are logged and harvested by human-operated hydraulic manipulators. Eventually, these tasks are expected to be automated with optimal performance. However, with todays technology the main problem is implementation. While prototypes may have rich sensing information, real cranes lack certain sensing devices, such as encoders for position sensing. Automating these machines requires unconventional solutions. In this paper, we consider the motion planning problem, which involves a redesign of optimal trajectories, so that open loop control strategies can be applied using feed-forward control signals whenever sensing information is not available.

  • 27.
    Ortiz Morales, Daniel
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    La Hera, Pedro
    Sveriges lantbruksuniversitet .
    Ur Rehman, Shafiq
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Generating Periodic Motions for the Butterfly Robot2013In: Intelligent Robots and Systems (IROS), 2013 IEEE/RSJ International Conference on / [ed] Amato, N., IEEE conference proceedings, 2013, p. 2527-2532Conference paper (Refereed)
    Abstract [en]

    We analyze the problem of dynamic non-prehensile manipulation by considering the example of thebutterfly robot. Our main objective is to study the problem of stabilizing periodic motions, which resemble some form of juggling acrobatics. To this end, we approach the problem by considering theframework of virtual holonomic constraints. Under this basis, we provide an analytical and systematic solution to the problems of trajectory planning and design of feedback controllers to guarantee orbital exponential stability. Results are presented in the form of simulation tests.

  • 28.
    Ortiz Morales, Daniel
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    La Hera, Pedro
    Sveriges lantbruksuniversitet .
    Westerberg, Simon
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Freidovich, Leonid
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Shiriaev, Anton
    Norwegian University of Science and Technology.
    Path-constrained motion analysis: an algorithm to understand human performance on hydraulic manipulators2015In: IEEE Transactions on Human-Machine Systems, ISSN 2168-2291, Vol. 45, no 2, p. 187-199Article in journal (Refereed)
    Abstract [en]

    We propose a novel method to analyze how human operators use hydraulic manipulators of heavy-duty equipment. The approach is novel in the sense that it applies knowledge of motion planning and optimization techniques used in robotics. As an example, we consider the case of operating a forestry crane. To that end, we use motion data that has been recorded during standard operation with the help of sensors and a data acquisition unit. The data backs up the notion that operators work by performing repeatable patterns observed in the trajectories of the manipulator's joints. We show how this nominal behavior is computed, and consequently this allow us to present the following: 1) an analytical procedure to analyze motions, 2) how to represent the "performance" of the operator in a 2D plot, 3) an example of how to use this information to suggest customized control settings, and 4) some complementary ideas needed for improving efficiency through automation.

  • 29.
    Ortiz Morales, Daniel
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    La Hera, Pedro X
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Design of energy efficient walking gaits for a three-link planar biped walker with two unactuated degrees of freedom2012In: Robotics and Automation (ICRA), 2012 IEEE International Conference on, New York: IEEE Computer Society, 2012, p. 148-153Conference paper (Other academic)
    Abstract [en]

    We consider the example of a three-link planar biped walker with two passive links. The main objective is to design symmetric periodic gaits in flat ground, that can be exponentially stabilized by feedback control. To this end, we apply recent advances in nonlinear control, to propose a systematic procedure to the problems of gait synthesis and control design. The core of the method lays on a nontrivial coordinate transformation, in order to approach the problem in a state-dependent form. For gait synthesis, such procedure allows a reduction of the search space, with the feasibility of considering energetic performance for optimization. For control design, this allows to apply concepts of transverse linearization, to design a nonlinear feedback control law, which performance is studied by numerical simulations.

  • 30.
    Ortiz Morales, Daniel
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Westerberg, Simon
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    La Hera, Pedro
    Sveriges lantbruksuniversitet .
    Mettin, Uwe
    Department of Transmission and Hybrid Systems, IAV Automotive Engineering, Berlin, Germany.
    Freidovich, Leonid
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Shiriaev, Anton
    Norwegian University of Science and Technology.
    Increasing the level of automation in the forestry logging process with crane trajectory planning and control2014In: Journal of Field Robotics, ISSN 1556-4959, E-ISSN 1556-4967, Vol. 31, no 3, p. 343-363Article in journal (Refereed)
    Abstract [en]

    Working with forestry machines requires great amount of training to be sufficiently skilledto operate forestry cranes. In view of this, introducing automated motions, as those seenin robotic arms, is ambitioned by this industry for shortening the amount of training timeand make the work of the operator easier. Motivated by this fact, we have developedtwo experimental platforms for testing control systems and motion planning algorithms inreal-time. They correspond to a laboratory setup and a commercial version of a hydraulicmanipulator used in forwarder machines. The aim of this article is to present the results ofthis development by providing an overview of our trajectory planning algorithm and motioncontrol method, with a subsequent view of the experimental results. For motion control,we design feedback controllers that are able to track reference trajectories based on sensormeasurements. Likewise, we provide arguments to design controllers in open-loop for thecase of machines lacking of sensing devices. Relying on the tracking efficiency of thesecontrollers, we design time efficient reference trajectories of motions that correspond tologging tasks. To demonstrate performance, we provide an overview of an extensive testingdone on these machines.

  • 31.
    Ortíz Morales, Daniel
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    La Hera, Pedro X
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Design of stable walking gaits for biped robots with several underactuated degrees of freedom2012In: Dynamic Walking Conference 2012, Pensacola, Florida, U.S.A., 2012Conference paper (Refereed)
    Abstract [en]

    Dynamic walking gaits are theoretically reflected by theperiodic solutions exhibited by nonlinear impulsive dynamicalsystems [1]. In practice, such solutions, knownas limit cycles, can exist either as a natural responseof the system, e.g. passive walkers, or by the use offeedback control. Analytically, finding these solutionsis certainly challenging, and the complexity of the problemincreases considerably if a mixture in between passiveand actuated joints are considered, i.e. underactuatedrobots.

  • 32.
    Ortíz Morales, Daniel
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Westerberg, Simon
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    La Hera, Pedro X.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Mettin, Uwe
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics. The Department of Engineering Cybernetics, Norwegian University of Science and Technology, Trondheim, Norway.
    Freidovich, Leonid
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Shiriaev, Anton S.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics. The Department of Engineering Cybernetics, Norwegian University of Science and Technology, Trondheim, Norway.
    Open-loop control experiments on driver assistance for crane forestry machines2011In: 2011 IEEE International Conference on Robotics and Automation (ICRA), IEEE conference proceedings, 2011, p. 1797-1802Conference paper (Refereed)
    Abstract [en]

    A short term goal in the forest industry is semi-automation of existing machines for the tasks of logging and harvesting. One way to assist drivers is to provide a set of predefined trajectories that can be used repeatedly in the process. In recent years much effort has been directed to the design of control strategies and task planning as part of this solution. However, commercialization of such automatic schemes requires the installation of various sensing devices, computers and most of all a redesign of the machine itself, which is currently undesired by manufacturers. Here we present an approach of implementing predefined trajectories in an open-loop fashion, which avoids the complexity of sensor and computer integration. The experimental results are carried out on a commercial hydraulic crane to demonstrate that this solution is feasible in practice.

  • 33.
    Westerberg, Simon
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Manchester, Ian
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Mettin, Uwe
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    La Hera, Pedro
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Shiriaev, Anton
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Virtual Environment Teleoperation of a Hydraulic Forestry Crane2008In: IEEE International Conference on Robotics and Automation, 2008, p. 4049-4054Conference paper (Refereed)
1 - 33 of 33
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