Hongqian Lu

Adaptive reaching law based sliding mode control for electromagnetic formation flight with input saturation

Abstract Electromagnetic formation flight utilizes electromagnetic forces to control the relative positions of satellites, and offers a promising alternative to a traditional propellant-based spacecraft formation flying due to no fuel expenditure. Since available electromagnetic forces generated on board are small, their efficient use is a challenging issue in the presence of saturation. This paper proposes a novel adaptive reaching law based sliding mode control for the trajectory tracking of electromagnetic formation flight with actuator saturation. The adaptive reaching law is characterized by a modulation function which combines a saturated term with a non-switching term. The saturated term makes the sliding variable converge as fast as possible under input saturation, while the non-switching term is used to guarantee a terminal tracking performance and remove chattering. Thus, the introduced modulation function enables a smooth transition of the reaching law between two terms and an adaptive decrease rate of sliding variable. The proposed control can achieve a fast convergence and offers the robustness against external disturbance with input saturation. Simulation results are given to demonstrate the performance of the presented method.

Principles and Applications of Polarized-light-aided Attitude Determination in Integrated Navigation

To improve the attitude error correcting capabilities of GPS/SINS integrated navigation systems, a new method of polarized-light-based GPS/SINS integrated navigation is presented. The principles of polarized-light-aided attitude determination are demonstrated, and a multi-module approach is proposed to increases the degree of observability. The integrated navigation algorithm is implemented in frame of federated Kalman filtering. To verify the effects of the method, Matlab simulation is performed. The results indicate that the degree of observability and precision of the navigation system can be obviously improved, and the performance of the system can be improved more by using multi-polarized-light modules whose lines of sight are non-parallel with each other.

Type-2 fuzzy logic control for underactuated truss-like robotic finger with comparison of a type-1 case1

Underactuated mechanical systems have their own difficulties within the control criterion. As a particular and complex underactuated mechanical system, underactuated truss-like robotic finger(UTRF) is studied by establishing its dynamic model. The control problems include high nonlinearity, model inaccuracy and uncertainties. Type-2 fuzzy logic control method is supposed to be a proper way to solve these problems, because fuzzy logic control itself does not depend on an accurate model of the controlled object, and type-2 fuzzy logic control is able to handle uncertainties. Based on a brief introduction on type-2 fuzzy logic systems, an interval type-2 fuzzy logic controller is designed for UTRF to accomplish the goal of stabilization in its equilibrium point. As an extension of the type-1 fuzzy, the performances of the proposed controller are compared with the type-1 one case to show the advantages of the type-2 fuzzy. Simulation results show that the designed interval type-2 fuzzy logic controller is correct and effective and has better performances than that of type-1 fuzzy control.

Quasi-finite-time control for high-order nonlinear systems with mismatched disturbances via mapping filtered forwarding technique

ABSTRACT In this study, a quasi-finite-time control method for designing stabilising control laws is developed for high-order strict-feedback nonlinear systems with mismatched disturbances. By using mapping filtered forwarding technique, a virtual control is designed to force the off-the-manifold coordinate to converge to zero in quasi-finite time at each step of the design; at the same time, the manifold is rendered insensitive to time-varying, bounded and unknown disturbances. In terms of standard forwarding methodology, the algorithm proposed here not only does not require the Lyapunov function for controller design, but also avoids to calculate the derivative of sign function. As far as the dynamic performance of closed-loop systems is concerned, we essentially obtain the finite-time performances, which is typically reflected in the following aspects: fast and accurate responses, high tracking precision, and robust disturbance rejection. Spring, mass, and damper system and flexible joints robot are tested to demonstrate the proposed controller performance.

Calibration and error analysis for polarized-light navigation sensor

In order to improve the calculation accuracy of polarized-light navigation sensor, the system error model was derived. Through the system error model, the system error source parameters could be calibrated outline, and the system error could be compensated greatly. The random error model was also derived in this paper. The transitive relation between random error and calculation accuracy of polarization direction was obtained. The transitive relation indicates that the angle error caused by random error is independent of polarization direction. According to this relation, the bound of angle error caused by random error could be calculated in real-time. The simulation results show that the system error model and random error model are correct and effective.

Observability of Geomagnetism/GPS/SINS integration during maneuvers

Observability of Geomagnetism/Global Positioning System/strapdown inertial navigation system (Geomagnetism/GPS/SINS) integrated system was analyzed during maneuvers. Instantaneous observability was adopted for the observability analysis of time-invariant and time-varying system. When there was no rotation relative to the Earth and the linear acceleration was constant, the system model became time-invariant. Observability analysis results show that there are at least one and at most two instantaneous unobservable states in the time-invariant Geomagnetism/GPS/SINS system, which are at least three in the time-invariant GPS/SINS system. The observability of time-varying system was analyzed for two types of maneuvers, nonconstant accelerating maneuvers and constant angular rate turn maneuvers. The sufficient conditions for instantaneous observability of system are presented for these two maneuvers. And the necessary condition for instantaneous observability is presented for nonconstant accelerating maneuvers. It is shown that the appropriate maneuver can enhance the instantaneous observability of system and all the states in Geomagnetism/GPS/SINS integrated system can be made instantaneous observable by appropriate maneuver.

A precise vision-based navigation method for autonomous soft landing of lunar explorer

During the entry, descent and landing (EDL) phase of the lunar explorer with a high degree of accuracy, the dual quaternion and the unscented Kalman filter (UKF) based vision navigation method is presented, in order to accomplish navigation task. The lunar explorers pose estimation method is developed through dual-quaternion calculation. The state equation is derived according to the dynamic model of the lunar explorer during the power descent phase, and the measurement equation is derived by constructing feature points triangle. Because of the nonlinear property of the state function and measurement function, the UKF method is used to estimate the pose of lunar explorer. Simulations demonstrate the validity of the proposed method.

Fast trajectory tracking of electromagnetic satellite formation with actuator saturation

Electromagnetic formation flight leverages electromagnetic force to control the relative position of satellites. This new propulsion technique offers a promising alternative to traditional propellant-based spacecraft formation flying since it does not consume fuel. Due to the restriction of maximum current in coils, the available inter-satellite electromagnetic force is small, and its efficient use is an important issue. In this paper, a modified far-field model is proposed to gain better accuracy of electromagnetic force approximation. Based on this model, an adaptive terminal sliding mode control is proposed to achieve fast trajectory tracking. The given method can guarantee the finite-time convergence of tracking error in the presence of bounded disturbance, input uncertainty, and saturation. Numerical simulation results demonstrate the performance and robustness of the proposed control.

Two novel robust tracking control strategies for eliminating aircraft wing rock

Nonlinearities are essential features in the model of aircraft wing rock system and limit cycle is a typical phenomenon when flying without any control force. In this work, we concentrate on two robust tracking control schemes for automatic flight control systems by using forwarding technique. Combining forwarding technique with adaptive control and disturbance observer, manifolds are represented as insensitivity to parameter uncertainties and external disturbances. A second-order filter is employed to compute mappings and their analytic derivatives at each step of the design. The global, uniform, and ultimate boundedness of all trajectories are guaranteed by internal stability of filters. Unlike some of the existing control methodologies, modularization and no differential operations together with reduction of computational load are the main advantages for practical applications. Scheme 1 requires no prior knowledge of unknown parameters and scheme 2 analyzes the convergence rate of uncertainty observers. Controller performance and comparison between two approaches are demonstrated via simulations.

Uncertainty observer-based robust tracking control for high-order nonlinear systems using forwarding technique

ABSTRACT Based on uncertainty observers, we develop a robust tracking control approach for high-order nonlinear systems subject to uncertainties satisfying mismatched condition. In this study, by combining with forwarding technique, uncertainty observers are designed to estimate uncertainties including parameter perturbations and external disturbances in a bottom-up way; at the same time, the convergence rate of estimate error of uncertainty observers is analysed in detail. The insensitivity to uncertainties for each manifold, no need of a prior knowledge on the bound of the uncertainty and the feasibility of practical implementation are three advantages of the proposed scheme. Moreover, approximate error of uncertainty observer can be made sufficiently small by tuning the parameters. The design procedures are elaborated and the boundedness of all trajectories of the closed-loop systems is guaranteed. Two examples are illustrated, highlighting the superiority of the proposed methodology via comparison with other control strategies.