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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.

  • 2. Liao, Qianfang
    et al.
    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 1941-0492Article 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

  • 3.
    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.

  • 4.
    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.

  • 5.
    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.

  • 6.
    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.
    Ren, Hongliang
    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.

  • 7.
    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 (1982. Print), 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.

  • 8.
    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.

  • 9.
    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.

  • 10.
    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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