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  • 1. Liao, Qianfang
    et al.
    Sun, Da
    Örebro University, School of Science and Technology.
    Interaction Measures for Control Configuration Selection Based on Interval Type-2 Takagi-Sugeno Fuzzy Model2018In: IEEE transactions on fuzzy systems, ISSN 1063-6706, E-ISSN 1941-0034, Vol. 26, no 5, p. 2510-2523Article in journal (Refereed)
    Abstract [en]

    Interaction measure determines decentralized and parse control configurations for a multivariable process control. This paper investigates interval type-2 Takagi–Sugeno fuzzy (IT2TSF) model based interactionmeasures using two different criteria, one is controllability and observability gramians, the other is relative normalized gain array (RNGA). The main contributions are: first, a data-driven IT2TSF modeling method is introduced; econd, explicit formulas to execute the two measures based on IT2TSF models are given; third, two interaction indexes are defined from RNGA to select sparse control configuration; fourth, the calculations to derive sensitivities of the two measures with respect to parametric variations in the IT2TSF models are developed; and fifth, the discussion to compare the two measures is presented. Three multivariable processes are used as examples to show that the results calculated from IT2TSF models are more accurate than that from their type-1 counterparts, and compared to gramian-basedmeasure, RNGA selectsmore reasonable control configurations and is more robust to the parametric uncertainties.

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    Type-1 and Type-2 Effective Tagaki-Sugeno Fuzzy Models for Decentralized Control of Multi-Input-Multi-Output Processes
  • 2.
    Liao, Qianfang
    et al.
    Örebro University, School of Science and Technology.
    Sun, Da
    Örebro University, School of Science and Technology.
    Sparse and Decoupling Control Strategies based on Takagi-Sugeno Fuzzy Models2019In: IEEE transactions on systems, man and cybernetics. Part B. Cybernetics, ISSN 1083-4419, E-ISSN 1941-0492, Vol. 51, no 2, p. 947-960Article in journal (Refereed)
    Abstract [en]

    In order to better handle the coupling effects when controlling multiple-input multiple-output (MIMO) systems, taking the decentralized control structure as the basis, this paper proposes a sparse control strategy and a decoupling control strategy. Type-1 and type-2 Takagi-Sugeno (T-S) fuzzy models are used to describe the MIMO system, and the relative normalized gain array (RNGA) based criterion is employed to measure the coupling effects. The main contributions include: i). compared to the previous studies, a manner with less computational cost to build fuzzy models for the MIMO systems is provided, and a more accurate method to construct the so-called effective T-S fuzzy model (ETSM) to express the coupling effects is developed; ii). for the sparse control strategy, four indexes are defined in order to extend a decentralized control structure to a sparse one. Afterwards, an ETSM-based method is presented that a sparse control system can be realized by designing multiple independent single-input single-output (SISO) control-loops; iii). for the decoupling control strategy, a novel and simple ETSM-based decoupling compensator is developed that can effectively compensate for both steady and dynamic coupling effects. As a result, the MIMO controller design can be transformed to multiple non-interacting SISO controller designs. Both of the sparse and decoupling strategies allow to use linear SISO control algorithms to regulate a closely coupled nonlinear MIMO system without knowing its exact mathematical functions. Two examples are used to show the effectiveness of the proposed strategies.

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    Sparse and Decoupling Control Strategies based on Takagi-Sugeno Fuzzy Models
  • 3.
    Liao, Qianfang
    et al.
    Örebro University, School of Science and Technology.
    Sun, Da
    Örebro University, School of Science and Technology.
    Andreasson, Henrik
    Örebro University, School of Science and Technology.
    FuzzyPSReg: Strategies of Fuzzy Cluster-based Point Set Registration2022In: IEEE Transactions on robotics, ISSN 1552-3098, E-ISSN 1941-0468, Vol. 38, no 4, p. 2632-2651Article in journal (Refereed)
    Abstract [en]

    This paper studies the fuzzy cluster-based point set registration (FuzzyPSReg). First, we propose a new metric based on Gustafson-Kessel (GK) fuzzy clustering to measure the alignment of two point clouds.  Unlike the metric based on fuzzy c-means (FCM) clustering in our previous work, the GK-based metric includes orientation properties of the point clouds, thereby providing more information for registration. We then develop the registration quality assessment of the GK-based metric, which is more sensitive to small misalignments than that of the FCM-based metric. Next, by effectively combining the two metrics, we design two FuzzyPSReg strategies with global optimization: i). \textit{FuzzyPSReg-SS}, which extends our previous work and aligns two similar-sized point clouds with greatly improved efficiency; ii). \textit{FuzzyPSReg-O2S}, which aligns two point clouds with a relatively large difference in size and can be used to estimate the pose of an object in a scene. In the experiment, we use different point clouds to test and compare the proposed method with state-of-the-art registration approaches. The results demonstrate the advantages and effectiveness of our method.

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    FuzzyPSReg: Strategies of Fuzzy Cluster-based Point Set Registration
  • 4.
    Liao, Qianfang
    et al.
    Örebro University, School of Science and Technology.
    Sun, Da
    Örebro University, School of Science and Technology.
    Andreasson, Henrik
    Örebro University, School of Science and Technology.
    Point Set Registration for 3D Range Scans Using Fuzzy Cluster-based Metric and Efficient Global Optimization2021In: IEEE Transactions on Pattern Analysis and Machine Intelligence, ISSN 0162-8828, E-ISSN 1939-3539, Vol. 43, no 9, p. 3229-3246Article in journal (Refereed)
    Abstract [en]

    This study presents a new point set registration method to align 3D range scans. In our method, fuzzy clusters are utilized to represent a scan, and the registration of two given scans is realized by minimizing a fuzzy weighted sum of the distances between their fuzzy cluster centers. This fuzzy cluster-based metric has a broad basin of convergence and is robust to noise. Moreover, this metric provides analytic gradients, allowing standard gradient-based algorithms to be applied for optimization. Based on this metric, the outlier issues are addressed. In addition, for the first time in rigid point set registration, a registration quality assessment in the absence of ground truth is provided. Furthermore, given specified rotation and translation spaces, we derive the upper and lower bounds of the fuzzy cluster-based metric and develop a branch-and-bound (BnB)-based optimization scheme, which can globally minimize the metric regardless of the initialization. This optimization scheme is performed in an efficient coarse-to-fine fashion: First, fuzzy clustering is applied to describe each of the two given scans by a small number of fuzzy clusters. Then, a global search, which integrates BnB and gradient-based algorithms, is implemented to achieve a coarse alignment for the two scans. During the global search, the registration quality assessment offers a beneficial stop criterion to detect whether a good result is obtained. Afterwards, a relatively large number of points of the two scans are directly taken as the fuzzy cluster centers, and then, the coarse solution is refined to be an exact alignment using the gradient-based local convergence. Compared to existing counterparts, this optimization scheme makes a large improvementin terms of robustness and efficiency by virtue of the fuzzy cluster-based metric and the registration quality assessment. In the experiments, the registration results of several 3D range scan pairs demonstrate the accuracy and effectiveness of the proposed method, as well as its superiority to state-of-the-art registration approaches.

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    Point Set Registration for 3D Range Scans Using Fuzzy Cluster-based Metric and Efficient Global Optimization
  • 5.
    Liao, Qianfang
    et al.
    School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore, Singapore.
    Sun, Da
    Department of Biomedical Engineering, National University, Singapore, Singapore.
    Cai, Wen-Jian
    School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore, Singapore.
    Li, Shao-Yuan
    Department of Automation, Shanghai Jiao Tong University, Shanghai, PR China.
    Wang, You-Li
    School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore, Singapore.
    Type-1 and Type-2 effective Takagi-Sugeno fuzzy models for decentralized control of multi-input-multi-output processes2017In: Journal of Process Control, ISSN 0959-1524, E-ISSN 1873-2771, Vol. 52, p. 26-44Article in journal (Refereed)
    Abstract [en]

    tEffective model is a novel tool for decentralized controller design to handle the interconnected inter-actions in a multi-input-multi-output (MIMO) process. In this paper, Type-1 and Type-2 effectiveTakagi-Sugeno fuzzy models (ETSM) are investigated. By means of the loop pairing criterion, simple cal-culations are given to build Type-1/Type-2 ETSMs which are used to describe a group of non-interactingequivalent single-input-single-output (SISO) systems to represent an MIMO process, consequently thedecentralized controller design can be converted to multiple independent single-loop controller designs,and enjoy the well-developed linear control algorithms. The main contributions of this paper are: i)Compared to the existing T-S fuzzy model based decentralized control methods using extra terms tocharacterize interactions, ETSM is a simple feasible alternative; ii) Compared to the existing effectivemodel methods using linear transfer functions, ETSM can be carried out without requiring exact mathe-matical process functions, and lays a basis to develop robust controllers since fuzzy system is powerful tohandle uncertainties; iii) Type-1 and Type-2 ETSMs are presented under a unified framework to provideobjective comparisons. A nonlinear MIMO process is used to demonstrate the ETSMs’ superiority overthe effective transfer function (ETF) counterparts as well as the evident advantage of Type-2 ETSMs interms of robustness. A multi-evaporator refrigeration system is employed to validate the practicabilityof the proposed methods.

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    fulltext
  • 6.
    Liao, Qianfang
    et al.
    Örebro University, School of Science and Technology.
    Sun, Da
    Örebro University, School of Science and Technology.
    Zhang, Shiyu
    Örebro University, School of Science and Technology.
    Loutfi, Amy
    Örebro University, School of Science and Technology.
    Andreasson, Henrik
    Örebro University, School of Science and Technology.
    Fuzzy Cluster-based Group-wise Point Set Registration with Quality Assessment2023In: IEEE Transactions on Image Processing, ISSN 1057-7149, E-ISSN 1941-0042, Vol. 32, p. 550-564Article in journal (Refereed)
    Abstract [en]

    This article studies group-wise point set registration and makes the following contributions: "FuzzyGReg", which is a new fuzzy cluster-based method to register multiple point sets jointly, and "FuzzyQA", which is the associated quality assessment to check registration accuracy automatically. Given a group of point sets, FuzzyGReg creates a model of fuzzy clusters and equally treats all the point sets as the elements of the fuzzy clusters. Then, the group-wise registration is turned into a fuzzy clustering problem. To resolve this problem, FuzzyGReg applies a fuzzy clustering algorithm to identify the parameters of the fuzzy clusters while jointly transforming all the point sets to achieve an alignment. Next, based on the identified fuzzy clusters, FuzzyQA calculates the spatial properties of the transformed point sets and then checks the alignment accuracy by comparing the similarity degrees of the spatial properties of the point sets. When a local misalignment is detected, a local re-alignment is performed to improve accuracy. The proposed method is cost-efficient and convenient to be implemented. In addition, it provides reliable quality assessments in the absence of ground truth and user intervention. In the experiments, different point sets are used to test the proposed method and make comparisons with state-of-the-art registration techniques. The experimental results demonstrate the effectiveness of our method.The code is available at https://gitsvn-nt.oru.se/qianfang.liao/FuzzyGRegWithQA

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    Fuzzy Cluster-based Group-wise Point Set Registration with Quality Assessment
  • 7.
    Stoyanov, Todor
    et al.
    Örebro University, School of Science and Technology.
    Krug, Robert
    Robotics, Learning and Perception lab, Royal Institute of Technology, Stockholm, Sweden.
    Kiselev, Andrey
    Örebro University, School of Science and Technology.
    Sun, Da
    Örebro University, School of Science and Technology.
    Loutfi, Amy
    Örebro University, School of Science and Technology.
    Assisted Telemanipulation: A Stack-Of-Tasks Approach to Remote Manipulator Control2018In: 2018 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS), IEEE Press, 2018, p. 6640-6645Conference paper (Refereed)
    Abstract [en]

    This article presents an approach for assisted teleoperation of a robot arm, formulated within a real-time stack-of-tasks (SoT) whole-body motion control framework. The approach leverages the hierarchical nature of the SoT framework to integrate operator commands with assistive tasks, such as joint limit and obstacle avoidance or automatic gripper alignment. Thereby some aspects of the teleoperation problem are delegated to the controller and carried out autonomously. The key contributions of this work are two-fold: the first is a method for unobtrusive integration of autonomy in a telemanipulation system; and the second is a user study evaluation of the proposed system in the context of teleoperated pick-and-place tasks. The proposed approach of assistive control was found to result in higher grasp success rates and shorter trajectories than achieved through manual control, without incurring additional cognitive load to the operator.

  • 8.
    Sun, Da
    et al.
    Örebro University, School of Science and Technology.
    Kiselev, Andrey
    Örebro University, School of Science and Technology.
    Liao, Qianfang
    Örebro University, School of Science and Technology.
    Stoyanov, Todor
    Örebro University, School of Science and Technology.
    Loutfi, Amy
    Örebro University, School of Science and Technology.
    A New Mixed Reality - based Teleoperation System for Telepresence and Maneuverability Enhancement2020In: IEEE Transactions on Human-Machine Systems, ISSN 2168-2305, Vol. 50, no 1, p. 55-67Article in journal (Refereed)
    Abstract [en]

    Virtual Reality (VR) is regarded as a useful tool for teleoperation system that provides operators an immersive visual feedback on the robot and the environment. However, without any haptic feedback or physical constructions, VR-based teleoperation systems normally have poor maneuverability and may cause operational faults in some fine movements. In this paper, we employ Mixed Reality (MR), which combines real and virtual worlds, to develop a novel teleoperation system. New system design and control algorithms are proposed. For the system design, a MR interface is developed based on a virtual environment augmented with real-time data from the task space with a goal to enhance the operator’s visual perception. To allow the operator to be freely decoupled from the control loop and offload the operator’s burden, a new interaction proxy is proposed to control the robot. For the control algorithms, two control modes are introduced to improve long-distance movements and fine movements of the MR-based teleoperation. In addition, a set of fuzzy logic based methods are proposed to regulate the position, velocity and force of the robot in order to enhance the system maneuverability and deal with the potential operational faults. Barrier Lyapunov Function (BLF) and back-stepping methods are leveraged to design the control laws and simultaneously guarantee the system stability under state constraints.  Experiments conducted using a 6-Degree of Freedom (DoF) robotic arm prove the feasibility of the system.

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    A New Mixed Reality - Based Teleoperation System for Telepresence and Maneuverability Enhancement
  • 9.
    Sun, Da
    et al.
    Örebro University, School of Science and Technology.
    Liao, Qianfang
    Örebro University, School of Science and Technology.
    A Framework of Robot Manipulability Learning and Control and Its Application in Telerobotics2024In: IEEE transactions on fuzzy systems, ISSN 1063-6706, E-ISSN 1941-0034, Vol. 32, no 1, p. 266-280Article in journal (Refereed)
    Abstract [en]

    Manipulability ellipsoid on the Riemannian manifold serves as an effective criterion to analyze, measure, and control the dexterous performance of robots. For asymmetric bilateral telerobotics, due to the different structures of master and slave robots, it is difficult or even impossible for the operator to manually regulate the manipulability of the remote slave robot. Thus, it is desired that the slave robot can automatically regulate its manipulability to assist the operator in remote different task executions, like humans regulating their own postures to enhance manipulability and adapt to different task scenarios. This article proposes a novel framework for manipulability transfer from human to robot. In this framework, we develop a Type-2 fuzzy model-based imitation learning method to encode and reproduce manipulability ellipsoids from demonstrations. This method can achieve high performance in accuracy and computational efficiency. In addition, it supports learning from a single demonstration. Then, we combine this method with a Riemannian manifold-based quadratic programming control algorithm such that the robot manipulability can fast track the desired manipulability profile. This framework is applied to telerobotics, in which a bilateral teleoperation controller is designed that enables the robot to follow the operator's command and simultaneously self-regulate its manipulability to perform the task adaptively. Meanwhile, the operator can receive force feedback relating to the manipulability regulation. Evaluations using comparative studies and practical experiments with a 3-DoF haptic device and 7-DoF robots are presented to show the effectiveness of the proposed framework.

  • 10.
    Sun, Da
    et al.
    Örebro University, School of Science and Technology.
    Liao, Qianfang
    Örebro University, School of Science and Technology.
    A Fuzzy Cluster-based Framework for Robot-Environment Collision Reaction2024In: IEEE transactions on fuzzy systems, ISSN 1063-6706, E-ISSN 1941-0034, Vol. 32, no 1, p. 75-89Article in journal (Refereed)
    Abstract [en]

    Environmental collision is a challenging issue in human-robot collaboration. This article proposes a novel fuzzy cluster-based framework for robots to have reactive responses to various environmental collision scenarios. This framework makes four contributions: First, a fuzzy cluster-based environmental collision detection algorithm is developed to efficiently classify the collision area and non-collision (free) area of the environment. Second, based on the collision detection algorithm, a p-norm approximation-based collision avoidance algorithm is proposed to enable robots to avoid environmental collisions with guaranteed stability. Third, by extending the collision avoidance algorithm, an environmental collision adaptation algorithm is proposed to allow robots to adapt to environmental collisions with intelligently regulated contact force. Fourth, a teleoperation controller is designed to strengthen haptic force rendering and enhance the operator’s perception of collisions. Going beyond existing methods, the proposed framework allows teleoperated robots to have real-time responses to collisions in quasi-static environments without suffering from local optima, where the environments can be unstructured, non-convex, and detected with noisy outliers. In addition, this framework is simple in implementation because the proposed collision avoidance and collision adaptation algorithms work as several linear Quadratic Programming (QP) constraints that can be flexibly used by Inverse Kinematics (IK) solvers. Several experiments using 7-Degree of Freedom (DoF) robots are conducted to test and compare the proposed framework with existing methods, demonstrating the effectiveness of our work.

  • 11.
    Sun, Da
    et al.
    Örebro University, School of Science and Technology.
    Liao, Qianfang
    Örebro University, School of Science and Technology.
    A Reactive Approach to Handling Multirobot Collision Based on p-Norm Approximation2023In: IEEE Transactions on Industrial Electronics, ISSN 0278-0046, E-ISSN 1557-9948Article in journal (Refereed)
    Abstract [en]

    In this article, we propose a new method for multi-robot systems to have reactive responses to various collision scenarios in real time. This method contains a novel p-norm approximation-based reactive approach, which allows multiple robots to avoid mutual collisions or to adapt to the collisions with intelligently regulated force. Compared with existing approaches, the implementation of the proposed method is simpler and more convenient since our reactive approach works as several linear Quadratic Programming (QP) constraints, allowing for flexible utilization by Inverse Kinematics (IK) solvers. In addition, it requires low computational complexity, achieves high accuracy, and does not need training. In the experiments, we employ a multi-robot system to conduct comprehensive comparisons between the proposed method and state-of-the-art approaches, effectively showcasing the efficacy of our work.

  • 12.
    Sun, Da
    et al.
    Örebro University, School of Science and Technology.
    Liao, Qianfang
    Örebro University, School of Science and Technology.
    Asymmetric Bilateral Telerobotic System with Shared Autonomy Control2021In: IEEE Transactions on Control Systems Technology, ISSN 1063-6536, E-ISSN 1558-0865, Vol. 29, no 5, p. 1863-1876Article in journal (Refereed)
    Abstract [en]

    The asymmetry in bilateral teleoperation, i.e., the differences of mechanical structures, sizes, and number of joints between the master and slave robots, can introduce kinematicsr edundancy and workspace inequality problems. In this article, a novel shared autonomy control strategy is proposed for handling the asymmetry of bilateral teleoperation, which has two main contributions. First, to deal with kinematics redundancy, the proposed strategy provides a self-regulation algorithm of orientation that allows the operator to solely use the master position command to simultaneously control the slave’s position and orientation. Second, to deal with workspace inequality, the proposed strategy enables the slave’s workspace to be dynamically tunable to adapt to various task spaces without influencing the smoothness of the robot’s movement. The experiments on a platform consisting of a six-degree of freedom (DoF) UR10 robot and a 3-DoF haptic device are given to validate the effectiveness of the proposed control strategy.

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    Asymmetric Bilateral Telerobotic System WithShared Autonomy Control
  • 13.
    Sun, Da
    et al.
    Örebro University, School of Science and Technology. Department of Biomedical Engineering, National University of, Singapore, Singapore.
    Liao, Qianfang
    Research & Development Center, Nidec Singapore Pte Ltd, Singapore, Singapore; Department of Biomedical Engineering, National University of ,Singapore, Singapore.
    Type-2 Fuzzy Logic based Time-delayed Shared Control in Online-switching Tele-operated and Autonomous Systems2018In: Robotics and Autonomous Systems, ISSN 0921-8890, E-ISSN 1872-793X, Vol. 101, p. 138-152Article in journal (Refereed)
    Abstract [en]

    This paper develops a novel shared control scheme for online-switching tele-operated and autonomous system with time-varying delays. Type-2 Takagi-Sugeno (T-S) fuzzy model is used to describe the dynamics of master and slave robots in this system. A novel non-singular fast terminal siding mode (NFTSM)-based algorithm combined with an extended wave-based time domain passivity approach (TDPA) is presented to enhance the master-slave motion synchronization in the tele-operated mode and reference-slave motion synchronization in the autonomous mode, while simultaneously ensuring the stability of the overall system in the presence of arbitrary time delays. In addition, based on the Type-2 Fuzzy model, a new torque observer is designed to estimate the external torques and then the torque tracking method is employed in the control laws to let the slave apply the designated force to further improve the operator’s force perception for the environment. The stability of the closed-loop system is proven using the Lyapunov-Krasovskii functions. Finally, experiments using two haptic devices prove the superiority of the proposed strategy.

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    Type-2 Fuzzy Logic based Time-delayed Shared Control in Online-switching Tele-operated and Autonomous Systems
  • 14.
    Sun, Da
    et al.
    Department of Biomedical Engineering, National University of Singapore, Singapore.
    Liao, Qianfang
    Department of Biomedical Engineering, National University of Singapore, Singapore.
    Gu, Xiaoyi
    Department of Biomedical Engineering, National University of Singapore, Singapore; NUS (Suzhou) Research Institute (NUSRI), Suzhou, China.
    Changsheng, Li
    Department of Biomedical Engineering, National University of Singapore, Singapore.
    Ren, Hongliang
    Department of Biomedical Engineering, National University of Singapore, Singapore; NUS (Suzhou) Research Institute (NUSRI), Suzhou, China; Singapore Institute for Neurotechnology (SINAPSE), Singapore.
    Multilateral Teleoperation With New Cooperative Structure Based on Reconfigurable Robots and Type-2 Fuzzy Logic2019In: IEEE Transactions on Cybernetics, ISSN 2168-2267, E-ISSN 2168-2275, Vol. 49, no 8, p. 2845-2859Article in journal (Refereed)
    Abstract [en]

    This paper develops an innovative multilateral teleoperation system with two haptic devices in the master side and a newly-designed reconfigurable multi-fingered robot hand in the slave side. A novel non-singular fast terminal sliding mode (NFTSM) algorithm together with varying dominance factors for cooperation is proposed to offer this system fast position and force tracking, as well as an integrate perception for the operator on the robot hand. Type-2 fuzzy model is used to describe the overall system dynamics, and accordingly a new fuzzy-model-based state observer is proposed to compensate for the system uncertainties. A sliding mode adaptive controller is designed to deal with the varying zero drift of the force sensors and force observers. The stability of the closed-loop system under time-varying delays is proved using Lyapunov-Krasovskii functions. Finally, experiments to grasp different objects are performed to verify the effectiveness of this multilateral teleoperation system.

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    A Multilateral Teleoperation System: New Cooperative Structure based on Reconfigurable Robot Hand and Controller Design based on Type-2 Fuzzy Model
  • 15.
    Sun, Da
    et al.
    Örebro University, School of Science and Technology.
    Liao, Qianfang
    Örebro University, School of Science and Technology.
    Kiselev, Andrey
    Örebro University, School of Science and Technology.
    Stoyanov, Todor
    Örebro University, School of Science and Technology.
    Loutfi, Amy
    Örebro University, School of Science and Technology.
    Shared mixed reality-bilateral telerobotic system2020In: Robotics and Autonomous Systems, ISSN 0921-8890, E-ISSN 1872-793X, Vol. 134, article id 103648Article in journal (Refereed)
    Abstract [en]

    This study proposes a new shared mixed reality (MR)-bilateral telerobotic system. The main contribution of this study is to combine MR teleoperation and bilateral teleoperation, which takes advantage of the two types of teleoperation and compensates for each other's drawbacks. With this combination, the proposed system can address the asymmetry issues in bilateral teleoperation, such as kinematic redundancy and workspace inequality, and provide force feedback, which is lacking in MR teleoperation. In addition, this system effectively supports long-distance movements and fine movements. In this system, a new MR interface is developed to provide the operator with an immersive visual feedback of the workspace, in which a useful virtual controller known as an interaction proxy—is designed. Compared with previous virtual reality-based teleoperation systems, this interaction proxy can freely decouple the operator from the control loop, such that the operational burden can be substantially alleviated. Additionally, the force feedback provided by the bilateral teleoperation gives the operator an advanced perception about the remote workspace and can improve task performance. Experiments on multiple pick-and-place tasks are provided to demonstrate the feasibility and effectiveness of the proposed system.

  • 16.
    Sun, Da
    et al.
    Örebro University, School of Science and Technology.
    Liao, Qianfang
    Örebro University, School of Science and Technology.
    Loutfi, Amy
    Örebro University, School of Science and Technology.
    Single Master Bimanual Teleoperation System with Efficient Regulation2020In: IEEE Transactions on robotics, ISSN 1552-3098, E-ISSN 1941-0468, Vol. 36, no 4, p. 1022-1037Article in journal (Refereed)
    Abstract [en]

    This paper proposes a new single master bimanual teleoperation (SMBT) system with an efficient position, orientation and force regulation strategy. Unlike many existing studies that solely support motion synchronization, the first contribution of the proposed work is to propose a solution for orientation regulation when several slave robots have differing motions. In other words, we propose a solution for self-regulated orientation for dual-arm robots. A second contribution in the paper allows the master with fewer degrees of freedom to control the slaves (with higher degrees of freedom), while the orientation of the slaves is self-regulated. The system further offers a novel force regulation that enables the slave robots to have a smooth and balanced robot-environment interaction with proper force directions. Finally, the proposed approach provides adequate force feedback about the environment to the operator and assists the operator in identifying different motion situations of the slaves. Our approach demonstrates that the forces from the slaves will not interrupt the operator’s perception of the environment. To validate the proposed system, experiments are conducted using a platform consisting of two 7-Degree of Freedom (DoF) slave robots and one 3-DoF master haptic device. The experiments demonstrated good results in terms of position, orientation and force regulation.

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    Single Master Bimanual Teleoperation System With Efficient Regulation
  • 17.
    Sun, Da
    et al.
    Örebro University, School of Science and Technology.
    Liao, Qianfang
    Örebro University, School of Science and Technology.
    Loutfi, Amy
    Örebro University, School of Science and Technology.
    Type-2 Fuzzy Model-based Movement Primitives for Imitation Learning2022In: IEEE Transactions on robotics, ISSN 1552-3098, E-ISSN 1941-0468, Vol. 38, no 4, p. 2462-2480Article in journal (Refereed)
    Abstract [en]

    Imitation learning is an important direction in the area of robot skill learning. It provides a user-friendly and straightforward solution to transfer human demonstrations to robots. In this article, we integrate fuzzy theory into imitation learning to develop a novel method called Type-2 Fuzzy Model-based Movement Primitives (T2FMP).In this method, a group of data-driven Type-2 fuzzy models are used to describe the input-output relationships of demonstrations. Based on the fuzzy models, T2FMP can efficiently reproduce the trajectory without high computational costs or cumbersome parameter settings. Besides, it can well handle the variation of the demonstrations and is robust to noise. In addition, we develop extensions that endow T2FMP with trajectory modulation and superposition to achieve real-time trajectory adaptation to various scenarios. Going beyond existing imitation learning methods, we further extend T2FMP to regulate the trajectory to avoid collisions in the environment that is unstructured, non-convex, and detected with noisy outliers. Several experiments are performed to validate the effectiveness of our method.

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    Type-2 Fuzzy Model-based Movement Primitives for Imitation Learning
  • 18.
    Sun, Da
    et al.
    National University of ,Singapore, Singapore.
    Liao, Qianfang
    National University of, Singapore, Singapore.
    Ren, Hongliang
    National University of, Singapore, Singapore.
    Type-2 Fuzzy Modeling and Control for Bilateral Teleoepration System With Dynamic Uncertianties and Time-Varying Delays2018In: IEEE Transactions on Industrial Electronics, ISSN 0278-0046, E-ISSN 1557-9948, Vol. 65, no 1, p. 447-459Article in journal (Refereed)
    Abstract [en]

    This paper develops data-driven Type-2 Takagi–Sugeno (T–S) fuzzy modeling and control for bilateral teleoperation with dynamic uncertainties and timevarying delays. The Type-2 T–S fuzzy model identified based on input–output data samples describes the nonlinear teleoperation system by a weighted sum of a group of linear local models, which offers a platform to design robust control algorithms by means of mature linear theories. The fuzzy-model-based four-channel control laws are proposed to guarantee the motion synchronization and enhance the operator’s force perception for the environment when the time-varying delays and large dynamic uncertainties, especially the gravity of a heavy end effector of the slave, exist. Markov processes are applied to model the time delays. The stability of the closed-loop system is proved by using the Lyapunov–Krasovskii functions. All the conditions are expressed as linear-matrix inequalities (LMI). By using the MATLAB LMI toolbox, the optimized control gains for each of the fuzzy rules are derived to achieve the optimal performance. Finally, experiments based on an experimental platform consisting of two haptic devices prove the superiority of the proposed strategy through comparison with previous work.

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    Type-2 Fuzzy Modeling and Control for Bilateral Teleoperation System with Dynamic Uncertainties and Time-varying Delays
  • 19.
    Sun, Da
    et al.
    Örebro University, School of Science and Technology.
    Liao, Qianfang
    Örebro University, School of Science and Technology.
    Stoyanov, Todor
    Örebro University, School of Science and Technology.
    Kiselev, Andrey
    Örebro University, School of Science and Technology.
    Loutfi, Amy
    Örebro University, School of Science and Technology.
    Bilateral telerobotic system using Type-2 fuzzy neural network based moving horizon estimation force observer for enhancement of environmental force compliance and human perception2019In: Automatica, ISSN 0005-1098, E-ISSN 1873-2836, Vol. 106, p. 358-373Article in journal (Refereed)
    Abstract [en]

    This paper firstly develops a novel force observer using Type-2 Fuzzy Neural Network (T2FNN)-based Moving Horizon Estimation (MHE) to estimate external force/torque information and simultaneously filter out the system disturbances. Then, by using the proposed force observer, a new bilateral teleoperation system is proposed that allows the slave industrial robot to be more compliant to the environment and enhances the situational awareness of the human operator by providing multi-level force feedback. Compared with existing force observer algorithms that highly rely on knowing exact mathematical models, the proposed force estimation strategy can derive more accurate external force/torque information of the robots with complex mechanism and with unknown dynamics. Applying the estimated force information, an external-force-regulated Sliding Mode Control (SMC) strategy with the support of machine vision is proposed to enhance the adaptability of the slave robot and the perception of the operator about various scenarios by virtue of the detected location of the task object. The proposed control system is validated by the experiment platform consisting of a universal robot (UR10), a haptic device and an RGB-D sensor.

  • 20.
    Sun, Da
    et al.
    School of Engineering and Information Sciences, University of Wollongong, Australia.
    Naghdy, Fazel
    School of Engineering and Information Sciences, University of Wollongong, Australia.
    Du, Haiping
    School of Engineering and Information Sciences, University of Wollongong, Australia.
    A novel approach for stability and transparency control of nonlinear bilateral teleoperation system with time delays2016In: Control Engineering Practice, ISSN 0967-0661, E-ISSN 1873-6939, Vol. 47, p. 15-27Article in journal (Refereed)
    Abstract [en]

    In this paper, a novel control approach is presented to improve the stability and transparency of the nonlinear bilateral teleoperation system with time delays, where a four-channel (4-CH) architecture using modified wave reflection reduction transformation is explored in order to guarantee the passivity of the communication channels in the nonlinear bilateral teleoperation system; a sliding-mode controller is proposed to compensate for the dynamic uncertainties and enhance the system synchronization performance in finite time. The system stability has been analyzed using Lyapunov functions. The proposed method is validated through experimental work based on a 3-DOF bilateral teleoperation platform in the presence of time delays. The experimental results clearly demonstrate that the proposed control algorithm has superiority on system transparency over other wave-based systems.

  • 21.
    Sun, Da
    et al.
    University of Wollogong, Wollogong, NSW, Australia.
    Naghdy, Fazel
    University of Wollogong, Wollogong, NSW, Australia.
    Du, Haiping
    University of Wollogong, Wollogong, NSW, Australia.
    Application of wave-variable control to bilateral teleoperation systems: A survey2014In: Annual Reviews in Control, ISSN 1367-5788, E-ISSN 1872-9088, Vol. 38, no 1, p. 12-31Article, review/survey (Refereed)
    Abstract [en]

    Teleoperation systems allow an operator to perform complex tasks in a remote environment. Stability of a bilateral teleoperation system is quite sensitive to time delays. One of the methods to guarantee the stability of bilateral telerobotics in the presence of time delays is wave variable control. A review of various applications of wave variable methods in telerobotics has been conducted. An evaluation of different methods proposed to compensate for the intrinsic problems associated with wave variable methods, including position drift, wave reflection and time varying delay, has also been carried out. In addition, different techniques developed to enhance the performance of the wave-based systems are also identified and reviewed. The research gaps in this field are identified and future directions for further research are proposed.

  • 22. Sun, Da
    et al.
    Naghdy, Fazel
    School of Engineering and Information Sciences, University of Wollongong, NSW, Australia.
    Du, Haiping
    School of Engineering and Information Sciences, University of Wollongong, NSW, Australia.
    Enhancing flexibility of the dual-master-dual-slave multilateral teleoperation system2015In: Proceedings of the IEEE Conference on Control Applications, ISSN 1085-1992, p. 300-305Article in journal (Refereed)
    Abstract [en]

    A flexible dual-master-dual-slave teleoperation system is proposed. On the master side, a new control law with a variable dominance factor is proposed to offer the system high flexibility and ease of training. A new wave-based Time Domain Passivity Approach (TDPA) is deployed to guarantee the channel passivity and high transparency in the presence of random time delays. The proposed algorithm is validated by applying it to a multilateral teleoperation platform consisting of four 3-DOF haptic devices configured as two masters and two slaves. The results demonstrate the feasibility of the proposed system in different complex tasks and its superior performance compared to previous work.

  • 23.
    Sun, Da
    et al.
    Faculty of Engineering and Information Sciences, University of Wollongong, Wollongong, Australia.
    Naghdy, Fazel
    Faculty of Engineering and Information Sciences, University of Wollongong, Wollongong, Australia.
    Du, Haiping
    Faculty of Engineering and Information Sciences, University of Wollongong, Wollongong, Australia.
    Neural Network-Based Passivity Control of Teleoperation System Under Time-Varying Delays2017In: IEEE Transactions on Cybernetics, ISSN 2168-2267, E-ISSN 2168-2275, Vol. 47, no 7, p. 1666-1680Article in journal (Refereed)
    Abstract [en]

    In this paper, a novel neural network (NN)-based four-channel wave-based time domain passivity approach (TDPA) is proposed for a teleoperation system with time-varying delays. The designed wave-based TDPA aims to robustly guarantee the channels passivity and provide higher transparency than the previous power-based TDPA. The applied NN is used to estimate and eliminate the system’s dynamic uncertainties. The system stability with linearity assumption on human and environment has been analyzed using Lyapunov method. The proposed algorithm is validated through experimental work based on a 3-DOF bilateral teleoperation platform in the presence of different time delays.

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    Neural Network based Passivity Control of Teleoperation System Under Time-Varying Delays
  • 24.
    Sun, Da
    et al.
    School of Electrical, Computer and Telecommunications Engineering, Faculty of Engineering and Information Sciences, University of Wollongong, Wollongong, Australia.
    Naghdy, Fazel
    School of Electrical, Computer and Telecommunications Engineering, Faculty of Engineering and Information Sciences, University of Wollongong, Wollongong, Australia.
    Du, Haiping
    School of Electrical, Computer and Telecommunications Engineering, Faculty of Engineering and Information Sciences, University of Wollongong, Wollongong, Australia.
    Stability Control of Force-Reflected Nonlinear Multilateral Teleoperation System under Time-Varying Delays2016In: Journal of Sensors, ISSN 1687-725X, E-ISSN 1687-7268, Vol. 2016, article id 4316024Article in journal (Refereed)
    Abstract [en]

    A novel control algorithm based on the modified wave-variable controllers is proposed to achieve accurate position synchronization and reasonable force tracking of the nonlinear single-master-multiple-slave teleoperation system and simultaneously guarantee overall system’s stability in the presence of large time-varying delays. The system stability in different scenarios of human and environment situations has been analyzed. The proposed method is validated through experimental work based on the 3-DOF trilateral teleoperation system consisting of three different manipulators. The experimental results clearly demonstrate the feasibility of the proposed algorithm to achieve high transparency and robust stability in nonlinear single-master-multiple-slave teleoperation system in the presence of time-varying delays.

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    Stability Control of Force-Reflected Nonlinear Multilateral Teleoperation System under Time-Varying Delays
  • 25.
    Sun, Da
    et al.
    School of Electrical, Computer and Telecommunication Engineering, Faculty of Engineering and Information Sciences, University of Wollongong, Wollongong, Australia.
    Naghdy, Fazel
    School of Electrical, Computer and Telecommunication Engineering, Faculty of Engineering and Information Sciences, University of Wollongong, Wollongong, Australia.
    Du, Haiping
    School of Electrical, Computer and Telecommunication Engineering, Faculty of Engineering and Information Sciences, University of Wollongong, Wollongong, Australia.
    Transparent four-channel bilateral control architecture using modified wave variable controllers under time delays2016In: Robotica (Cambridge. Print), ISSN 0263-5747, E-ISSN 1469-8668, Vol. 34, no 4, p. 859-875Article in journal (Refereed)
    Abstract [en]

    Stability and transparency are two critical indices of bilateral teleoperation systems. The wave variable method is a conservative approach to robustly guarantee system passivity under arbitrary constant time delays. However, the wave-variable-based reflection is an intrinsic problem in this method because it can significantly degrade system transparency and disorient the operator’s perception of the remote environment. In order to enhance both the transparency and the stability of bilateral teleoperation systems in the presence of large time delays, a new four-channel (4-CH) architecture is proposed which applies two modified wave-transformation controllers to reduce wave-based reflections. Transparency and stability of the proposed system are analyzed and the improvement in these when using this method is measured experimentally. Results clearly demonstrate that the proposed method can produce high transparency and stability even in the presence of large time delays.

  • 26.
    Sun, Da
    et al.
    University of Wollongong, Wollongong, N.S.W., Australia.
    Naghdy, Fazel
    School of Electrical, Computer and Telecommunications Engineering, University of Wollongong, Wollongong, N.S.W., Australia.
    Du, Haiping
    School of Electrical, Computer and Telecommunications Engineering, University of Wollongong, Wollongong, N.S.W., Australia.
    Wave-Variable-Based Passivity Control of Four-Channel Nonlinear Bilateral Teleoperation System Under Time Delays2016In: IEEE/ASME transactions on mechatronics, ISSN 1083-4435, E-ISSN 1941-014X, Vol. 21, no 1, p. 238-253Article in journal (Refereed)
    Abstract [en]

    An innovative wave-based time-domain passivity approach applied to a four-channel nonlinear teleoperation system is proposed. The primary objective of this approach is to enhance system transparency while maintaining stability in the presence of random time delays. The system stability for different scenarios of human and environment condition is analyzed. The method is validated through experimental work based on a 3-DOF bilateral teleoperation system. The experimental results show that the proposed control algorithm can robustly guarantee the system stability, and simultaneously provide better performance than methods developed in previous work.

  • 27.
    Sun, Da
    et al.
    National University of Singapore, Singapore, Singapore.
    Naghdy, Fazel
    University of Wollongong, Wollongong, Australia.
    Du, Halping
    University of Wollongong, Wollongong, Australia.
    Time domain passivity control of time-delayed bilateral telerobotics with prescribed performance2017In: Nonlinear dynamics, ISSN 0924-090X, E-ISSN 1573-269X, Vol. 87, p. 1253-1270Article in journal (Refereed)
    Abstract [en]

    A novel approach applying the extended prescribed performance control (PPC) and the wavebased time domain passivity approach (wave-based TDPA) to teleoperation systems is proposed. With the extended PPC, a teleoperation system can synchronize position, velocity and force. Moreover, by combining with the extended wave-based TDPA, the overall system’s passivity is guaranteed in the presence of arbitrary time delays. The system’s stability and performance are analyzed by using Lyapunov functions. The method is validated through experimental work based on a 3-DOF bilateral teleoperation system. The experimental results showthat the proposed control algorithm can robustly guarantee the master–slave system’s passivity and simultaneously provide high tracking performance of position, velocity and measured force signals.

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    Time Domain Passivity Control of Time Delayed Telerobotics with Prescribed Performance
1 - 27 of 27
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