Xuzhi Lai

Central South University, Ch’ang-sha-shih, Hunan, China

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Publications (14)12.02 Total impact

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    ABSTRACT: This paper concerns the global stabilization of an underactuated spring-coupled three-link horizontal manipulator (STHM), which is an underactuated mechanical system (UMS) with two actuators and three degrees of freedom (DOF). A new control method is developed that asymptotically stabilizes the STHM at the origin using the position measurements of the manipulator only. First, we introduce a homeomorphic coordinate transformation for the STHM system. This changes the stabilization of the STHM into that of the transformed system. Next, we analyze the characteristics of the transformed system. After that, we construct an equivalent-input-disturbance- (EID-) based control system to globally stabilize the transformed system at the origin. Finally, a numerical example demonstrates the validity of the presented method. Our method only uses the position measurements of the STHM to design stabilizing controller. It reduces the cost of the whole control system and avoids the influence on the system’s control performance imposed by velocity noises. In addition, the analysis and control method of this paper is easy to extend to the global stabilization of other n -DOF (n⩾3n⩾3) UMSs.
    Applied Mathematical Modelling 01/2014; · 2.16 Impact Factor
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    ABSTRACT: An underactuated three-link gymnast robot (UTGR) is a simple model of a gymnast on a high bar. The control objective of a UTGR is to swing it up from a point near the straight-down position and to stabilize it at the straight-up position. To achieve this, we first divide the motion space into two subspaces, swing-up area and balancing area, and design a controller for each. The design of a swing-up control law that ensures that the UTGR enters the balancing area is crucial because the UTGR is subject to a nonholonomic constraint and is highly nonlinear during the swing-up motion. This study focused on how to design a swing-up control law that contains no singularities. The key concept is the introduction of a virtual coupling between control torques, which converts the problem of avoiding singularities to one of imposing constraints on the parameters of the control law and properly selecting those parameters. A swing-up control law thus designed ensures that the UTGR enters the balancing area in a natural stretched-out posture. This makes it easy to stabilize the UTGR in the balancing area. Copyright © 2013 John Wiley & Sons, Ltd.
    International Journal of Robust and Nonlinear Control 09/2013; · 1.90 Impact Factor
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    ABSTRACT: This paper concerns motion planning and tracking control for an acrobot. We first introduce an artificial friction torque in order to construct a downward trajectory, and rewind it to make an upward trajectory. Then, we combine the upward trajectory with a stabilizing trajectory to make a complete trajectory. Finally, we use the pole assignment method to design a tracking controller that makes the acrobot exponentially track the whole trajectory. This enables the acrobot to be swung up from the straight-down position and stabilized at the straight-up position. Unlike the most commonly used switching stabilization control methods, the strategy presented here features a single controller for motion control in the whole motion space. It is simple and efficient. Simulation results demonstrate the validity of the method.
    Automatica 01/2013; 49(1):278–284. · 2.92 Impact Factor
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    ABSTRACT: This paper designs a new three-dimensional chaotic system with a simple structure and only a nonlinear term, it contains three design parameters. We demonstrate the system is chaotic theoretically by the stability analysis of the equilibrium point, Lyapunov index calculation, and bifurcation phenomenon of the system when design parameter changes. Finally, numerical simulation shows that a typical chaotic attractor happens in this system by using MATLAB software, and the period-doubling bifurcation phenomenon is observed according to the bifurcation diagram. The simulation results prove that the system possesses the characteristics of chaos.
    Control and Decision Conference (CCDC), 2013 25th Chinese; 01/2013
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    ABSTRACT: This paper presents a generalized predictive control (GPC) strategy with closed-loop model identification for burn-through point (BTP) control in the sintering process. First, the dynamic Auto-Regressive eXogenous (ARX) model structure is defined to describe sintering process. Considering the economy and security, a closed-loop identification method is adopted to update the parameters of the model. Then, BTP predictive control model is established based on GPC algorithm to predict BTP accurately and to calculate the strand velocity. Finally, a BTP control system is established and implemented in an iron and steel plant. The running results show that the system effectively guarantees the stability of sintering process and suppresses the fluctuation of BTP.
    Control Engineering Practice 10/2012; 20(10):1065–1074. · 1.67 Impact Factor
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    ABSTRACT: This paper presents a unified treatment of the motion control of underactuated two-link manipulators, including Acrobot and Pendubot. The motion space is divided into two areas: swing-up and attractive, and control laws are designed for each. First, a control law based on a Weak-Control Lyapunov Function (WCLF) is employed to increase the energy of the system and control the posture of the actuated link in the swing-up area. Next, a parameter in the WCLF is chosen to be a nonlinear function of the state so as to avoid any singularities. Then, another design parameter in the control law based on WCLF is adjusted based on the state to improve the control performance. The stability of the swing-up area is guaranteed by the use of a WCLF based on the largest invariant set theorem. And a Non-Smooth Lyapunov Function (NSLF) is employed to guarantee stability after the manipulator leaves the swing-up area. Finally, the global stability of the control system is guaranteed by the combination of a WCLF and a NSLF.
    ACTA AUTOMATICA SINICA 01/2008; 34(1).
  • Ning Chen, Xuzhi Lai, Changbing Lu
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    ABSTRACT: An improved reducing peak-to-average power ratio (PAPR) method which called Controller Clipper is presented for the problem of high PAPR of orthogonal frequency division multiplexing (OFDM). Based on the kernel formed on the tone reservation, the kernel is circular shifted to the maximum peak value, which will be reduced. Code error rate is not increased in the process, and the result is obvious in reducing PAPR. The effectiveness of the proposed scheme is demonstrated by simulations.
    Proceedings of the 9th International Conference for Young Computer Scientists, ICYCS 2008, Zhang Jia Jie, Hunan, China, November 18-21, 2008; 01/2008
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    ABSTRACT: This paper presents a controller design and global stability analysis of Acrobots based on non-smooth Lyapunov functions. Three control laws that are derived based on three Lyapunov functions are applied successively to achieve a suitable posture and increase the energy so as to stabilize the Acrobot at an unstable inverted equilibrium position. LaSalle invariant theorem and non-smooth Lyaunov function are employed to theoretically guarantee the stability of the Acrobot in the whole motion space. Simulation results demonstrate the validity of this strategy.
    ACTA AUTOMATICA SINICA 01/2007; 33(7).
  • Kongzhi Lilun Yu Yinyong/Control Theory and Applications 01/2000; 17(3).
  • Xuzhi Lai, Zixing Cai, Jinhua She
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    ABSTRACT: Presents a control strategy for underactuated mechanical system: the acrobot example, which combines fuzzy control and linear quadratic control. The fuzzy controller designed for the upswing ensures that the energy of the acrobot increases with each swing. After the acrobot enters a neighborhood of the unstable straight-up equilibrium position, a linear quadratic regulator is designed to balance it.
    Journal of Central South University of Technology 10/1999; 6(2):134-137. · 0.36 Impact Factor
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    ABSTRACT: This paper describes a fuzzy control strategy for the control of an acrobot. The strategy combines model-free and model-based fuzzy control. The model- free fuzzy controller designed for the upswing ensures that the energy of the acrobot increases with each swing. The model-based fuzzy controller, which is based on a Takagi- Sugeno fuzzy model for balancing, employs the concept of parallel distributed compensation. The stability of the fuzzy control system for balance control is guaranteed by a common symmetric positive matrix, which satisfies linear matrix inequalities.
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    ABSTRACT: This paper presents a new method of globally stabilizing a non-linear underactuated mechanical system with two degrees of freedom (DOF). It is based on the idea of equivalent input disturbance (EID), and designing the controller requires only the state variables of position, not velocity. The design procedure has two steps: (1) Use a global homeomorphic coordinate transformation to convert the original system into a new non-linear system. This changes the problem of stabilizing the original system into one of stabilizing the new system. (2) Divide the new system into linear and non-linear parts and take the non-linear part to be an artificial disturbance, thereby enabling use of the EID approach to globally asymptotically stabilize the new system at the origin. The new method was tested through numerical simulations on three well-known 2-DOF underactuated mechanical systems (TORA, beam ball, inertia wheel pendulum). The results demonstrate its validity and its superiority over others.
    Nonlinear Dynamics 69(1-2). · 3.01 Impact Factor
  • XUZHI LAI, ZIXING CAI, JIN-HUA SHE
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    ABSTRACT: This paper describes a control strategy for the control of an acrobot. The strategy combines a model-free fuzzy control, a fuzzy sliding-mode control and a model-based fuzzy control. The model-free fuzzy controller designed for the upswing ensures that the energy of the acrobot increases with each swing. Then the fuzzy sliding-mode controller is employed to control the movement that the acrobot enters the attractive area from the swing-up area. The model-based fuzzy controller, which is based on a Takagi-Sugeno fuzzy model is used to balance the acrobot. The stability of the fuzzy control system for balance control is guaranteed by a common symmetric positive matrix, which satisfies linear matrix inequalities.
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    ABSTRACT: This paper concerns the global stabilization control of an underactuated two-link acrobot in a vertical plane using a new control method based on an equivalent-input-disturbance (EID) approach. The design procedure consists of two steps: (1) A homeomorphous coordinate transformation transforms the acrobot system into a new nonlinear system. (2) The new system is divided into linear and nonlinear parts, and the nonlinear part is taken to be an artificial disturbance. Then, the EID-based approach is used to globally and asymptotically stabilize the system at the origin. This method enables the acrobot to be swung up from any initial position and balanced at the straight-up position. Unlike the most commonly used switching control method, ours features a single controller for both swing-up and balancing control. Simulation results demonstrate the validity of the method.