Search

Summary In this paper, an output-feedback adaptive consensus tracking control scheme is proposed for a class of high-order nonlinear multi-agent systems. The agents are allowed to have unknown parameters, unknown nonlinearities, and input quantization simultaneously. The desired trajectory to be tracked is available for only a subset of agents, and only the relative outputs and the quantized inputs need to be measured or transmitted as signal exchange among neighbors regardless of the system order. By introducing a kind of high-gain K-filters and a smooth function, the effect among agents caused by the unknown nonlinearities is successfully counteracted, and all closed-loop signals are proved to be globally uniformly bounded. Moreover, it is shown that the tracking errors converge to a residual set that can be made arbitrarily small. Simulation results on robot manipulators are presented to illustrate the effectiveness of the proposed scheme. Copyright © 2017 John Wiley & Sons, Ltd.

Summary This paper deals with the task-space trajectory tracking control problem of robot manipulators. An improved adaptive backstepping controller is proposed to deal with the uncertainties in kinematics, dynamics, and actuator modeling. To avoid the explosion of computation in conventional backstepping techniques, a modified dynamic surface control algorithm is proposed, which guarantees the asymptotic convergence rather than the uniformly ultimately boundedness of tracking errors in conventional dynamic surface control methods. Furthermore, the expression of the ℒ2 norm of tracking errors is explicitly derived in relation to the controller parameters, which provides instructions on tuning controller parameters to adjust the system performance. Moreover, the passivity structure of the designed adaptation law is thoroughly analyzed. Simulation of a free-floating space robot is used to verify the effectiveness of the proposed control strategy in comparison with the conventional tracking control schemes. Copyright © 2016 John Wiley & Sons, Ltd.

Summary A unified solution is presented to the tracking control problem of Euler–Lagrange systems with finite-time convergence. A reconstruction module is designed to estimate the overall of unmodeled dynamics, disturbance, actuator misalignment, and multiple actuator faults. That reconstruction is accomplished in finite time with zero error. A nonsingular terminal sliding mode controller is then synthesized, and the resultant closed-loop system is also shown to be finite-time stable with the reference trajectory followed in finite time. Unlike most sliding mode control methods to handle system uncertainties, the designed control has less conservativeness and stronger fault tolerant capability. A rigid spacecraft system is used to demonstrate the effectiveness and potential of the proposed scheme. Copyright © 2014 John Wiley & Sons, Ltd.

A novel saturated proportional-derivative control incorporated with null-space-based optimal control reallocation is proposed for spacecraft attitude stabilization in the presence of disturbance and input saturation. More specifically, a saturated proportional-derivative based baseline nonlinear controller is firstly developed to guarantee the globally asymptotic stability under input constraints and external disturbance. This is achieved with inexpensive online computations by dynamically adjusting a single parameter to ensure the desired performance. Then, a novel null-space-based optimal control reallocation method is employed to map the specified virtual control command to the redundant actuators. The optimal control solution is obtained by penalizing the control allocation errors at a lower power/energy cost using quadratic programming algorithm. The benefits of the proposed control method are analytically authenticated and also validated via simulation study.

SUMMARY The problem of fault tolerant attitude stabilization with finite-time convergence is investigated for spacecraft with redundant actuators. On the basis of the sliding mode control technique, a robust controller is derived with uncertain inertia parameters, actuator faults, and external disturbances explicitly addressed. It is shown that finite-time reachability into the small neighborhood of sliding surface, and faster time convergence of attitude orientation are achieved. To address actuator input constraints, an adaptive fault tolerant controller is further proposed. One feature of the proposed strategy is that the design of the fault tolerant control does not require any fault detection and isolation mechanism to detect, separate, and identify actuator faults. The attitude stabilization performance using the controller is evaluated through a numerical example. Copyright © 2012 John Wiley & Sons, Ltd.

SUMMARY A theoretical framework for active fault-tolerant attitude stabilization control is developed and applied to flexible spacecraft. The proposed scheme solves a difficult problem of fault-tolerant controller design in the presence of severe partial loss of actuator effectiveness faults and external disturbances. This is accomplished by developing an observer-based fault detection and diagnosis mechanism to reconstruct the actuator faults. Accordingly, a backstepping-based fault-tolerant control law is reconfigured using the reconstructed fault information. It is shown that the proposed design approach guarantees that all of the signals of the closed-loop system are uniformly ultimately bounded. The closed-loop performance of the proposed control strategy is evaluated extensively through numerical simulations. Copyright © 2012 John Wiley & Sons, Ltd.

Adaptive control design using neural networks (a) is investigated for attitude tracking and vibration stabilization of a flexible spacecraft, which is operated at highly nonlinear dynamic regimes. The spacecraft considered consists of a rigid body and two flexible appendages, and it is assumed that the system parameters are unknown and the truncated model of the spacecraft has finite but arbitrary dimension as well, for the purpose of design. Based on this nonlinear model, the derivation of an adaptive control law using neural networks (NNs) is treated, when the dynamics of unstructured and state-dependent nonlinear function are completely unknown. A radial basis function network that is used here for synthesizing the controller and adaptive mechanisms is derived for adjusting the parameters of the network and estimating the unknown parameters. In this derivation, the Nussbaum gain technique is also employed to relax the sign assumption for the high-frequency gain for the neural adaptive control. Moreover, systematic design procedure is developed for the synthesis of adaptive NN tracking control with L2 -gain performance. The resulting closed-loop system is proven to be globally stable by Lyapunov's theory and the effect of the external disturbances and elastic vibrations on the tracking error can be attenuated to the prescribed level by appropriately choosing the design parameters. Numerical simulations are performed to show that attitude tracking control and vibration suppression are accomplished in spite of the presence of disturbance torque/parameter uncertainty. Copyright © 2009 John Wiley & Sons, Ltd.

An integral-type sliding mode control (SMC) scheme with application to track-following control in hard disk drives (HDDs) is investigated in this paper. With the proposed technique, the dynamics of the sliding mode is analytically obtained without any reaching phase by using the integral sliding surface. To reconstruct estimates of the system states for use in a full information SMC law, an asymptotic observer is also employed and the fulfillment of sliding condition, including the case when estimated states are used, is also verified. In addition, the proposed control scheme integrated with a phase lead peak filter (PLPF) is also investigated for better rejection of disturbance of narrow-band type at mid-frequency ranges. Simulation studies on the design of a track-following controller in HDDs are conducted to illustrate its feasibility and effectiveness. The simulation results also demonstrate that the proposed scheme provides better performance than the conventional sliding mode and proportional–integral–derivative control methods. Copyright © 2007 John Wiley & Sons, Ltd.

This investigation is to apply optimal sliding mode (OSM) control theory and distributed piezoelectric sensor/actuator technology to vibration control of a flexible spacecraft. An approximate analytical dynamic model of a slewing flexible spacecraft with surface-bonded piezoelectric sensors/actuators is developed using Hamilton's principle with discretization by assumed model method. To satisfy pointing requirements and simultaneously suppress vibration, two separate control loops are adopted. The first uses the piezoceramics as sensors and actuators to actively suppress certain flexible modes by designing a positive position feedback (PPF) compensators that add damping to the flexible structures in certain critical modes in the inner feedback loop; then a second feedback loop is designed using OSM control to slew the spacecraft. The OSM controller minimizes the expected value of a quadratic objective function consisting of only the states with the constraints that the error states always remain on the intersection of sliding surfaces. The advantage in this method is that the vibration reduction and attitude control are achieved separately in the two separate feedback loops, allowing the pointing requirements and simultaneous vibrations suppression to be satisfied independently of one another. An additional attraction of the design method is that the selection of PPF gain is determined by introducing a cost function to be minimized by the feedback gains which are subject to the stability criterion at the same time, such that the feedback gains are selected in a more systematical way to avoid the arbitrary selecting of feedback gains. The proposed control strategy has been implemented on a flexible spacecraft, which is a hub with a cantilever flexible beam appendage and can undergo a single axis rotation. Both analytical and numerical results are presented to show the theoretical and practical merits of this approach. Copyright © 2006 John Wiley & Sons, Ltd.