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We propose a reliability-based anti-disturbance control (RADC) method for systems with parametric stochastic uncertainty based on the linear matrix inequality (LMI) and the limit state function. Differing from the existing anti-disturbance control, the parametric stochastic uncertainty is considered in both the concerned system and the exogenous disturbance system. With this consideration, the condition for system stability and performance robustness is described by a stochastic LMI which holds with a certain probability (reliability). Through the limit state function method, the stochastic LMI is subtly transformed into two probabilistic LMIs for two different cases. The proposed probabilistic LMIs contain two probabilistic parameters of reliability indexes that quantify the effect of parametric stochastic uncertainty. At different prescribed reliability indexes, controllers with different reliability can be flexibly and reliably designed. Two illustrative examples with Monte-Carlo verification are presented to demonstrate the feasibility and effectiveness of the proposed RADC method. • A reliability model for uncertain systems is established by stochastic LMI. • A novel concept/method of probabilistic LMI for RADC is proposed. • The proposed RADC greatly extends the application of traditional LMI. [ABSTRACT FROM AUTHOR]

The reaction wheel is a typical actuator and a crucial weak link in the spacecraft attitude control system, and much attention has been paid to its reliability problem. Due to limited samples and high cost for reaction wheel life tests, a simulation method by introducing attitude coupling dynamics and multiplicative fault concept is developed to analyze the logic of electric current as a performance indicator and verify its accuracy for reliability modeling. Furthermore, a new and intrinsic performance indicator of multiplicative fault is proposed for more application scenarios of reliability modeling and an adaptive sliding mode observer is designed for fault estimation. An illustrative example shows that the performance indicator of multiplicative fault can be used for various mission scenarios but requires certain persistent excitation, while electric current is the opposite. • A simulation method for analyzing current as a performance indicator is developed. • Multiplicative fault is introduced as a new performance indicator. • An adaptive sliding mode fault observer is designed. • The application scenarios of two performance indicators are analyzed. [ABSTRACT FROM AUTHOR]

Alzheimer's disease (AD) is a central nervous system disease that mainly appears in the aged. Early diagnosis of AD is valuable in delaying the progression of the disease. With the development of medical imaging technology, various medical images such as structural Magnetic Resonance Imaging (sMRI) and Fluorodeoxyglucose Positron Emission Tomography (FDG-PET) can obtain the structural and functional lesions of the brain to assist in diagnosing diseases. However, FDG-PET is usually incomplete due to radiation and high costs. Most existing methods exclude missing modal subjects, which is remarkably one-sided. Meanwhile, how to extract the features of different levels of multimodal fusion is still a challenge. To solve these issues, we propose a Consistent Manifold Projection Generative Adversarial Network (CMPGAN) for FDG-PET generation and a Multilevel Multimodal Fusion Diagnosis Network (MMFDN) for diagnosing AD. First, we propose a CMPGAN model to project the distribution onto low-dimensional manifolds through consistent manifold projection, and present a distribution distance metric to optimize the model. Our proposed model can avoid problems of mode collapse and gradient disappearance. Then, we construct a multiscale feature-level feature extraction network based on our proposed radial medley unit and a voxel-level feature extraction network based on a harmonic voxel fusion matrix. The fusion of the two parts obtains the final diagnosis result. Experimental results indicate that our proposed method performs better than state-of-the-art methods in FDG-PET generation and AD diagnosis. Our approach also has the significance of guiding clinicians in diagnosing diseases. • A multimodal Alzheimer's disease computer aided diagnosis method is proposed. • The proposed generator network realizes FDG-PEET completion. • A multiscale feature-level and voxel-level fusion diagnosis model is proposed. • The proposed method effectively solves the problem of modal hiatus in clinical. [ABSTRACT FROM AUTHOR]

Abstract Precise and fast attitude maneuvers are a requirement in many future space missions. However, the actuator deviation fault of micro satellite is inevitable, which affects the precision of spacecraft pointing. To overcome this difficulty, this paper presents a novel attitude control scheme to compensate the actuator deviation fault and achieve the finite-time attitude maneuver. Moreover, the proposed control scheme is constituted by an outer attitude tracking loop and an inner angular velocity tracking loop according to dynamic features of micro satellite. In the outer loop, a novel virtual control law, namely a desired angular velocity command, is developed, under which the finite-time attitude tracking can be achieved. Furthermore, in the inner loop, an effective composite controller which consists of a terminal sliding mode controller and a finite-time disturbance observer (FTDO) is proposed. The aim of composite controller is to ensure that the angular velocity can track the virtual control law in finite time, where the FTDO is designed to estimate and compensate the actuator deviation fault in the feed-forward channel. Finally, simulation results are conducted to demonstrate the effectiveness of the proposed control scheme. [ABSTRACT FROM AUTHOR]

Abstract As well-known disturbance rejection methods, active disturbance rejection control and disturbance observer-based control can effectively improve the control performances of complex systems in the presence of disturbances. However, the accurate rejection of multiple disturbances for control systems of practical engineering, for example, the attitude control system of flexible spacecraft, is still a bottleneck problem. In order to further improve the anti-disturbance capability and reduce the conservativeness, this paper proposes a novel enhanced anti-disturbance control law for the attitude control system of flexible spacecraft by combining active disturbance rejection control and disturbance observer-based control in a unified framework. More specifically, the disturbance from flexible vibration is described by an uncertain exogenous system based on the partially known information including elastic damping ratios and modal frequencies. The disturbance observer-based control is utilized to estimate and thereby reject this disturbance. On the other hand, the other disturbances such as external environmental disturbance and complex model nonlinearity are merged into a equivalent disturbance with bounded derivative, which is compensated by using the active disturbance rejection control law. Stability and robustness analysis are carried out for the disturbance observer and extended state observer. Finally, simulation results of low-earth-orbit flexible satellite are presented to verify the effectiveness of proposed methods. [ABSTRACT FROM AUTHOR]

This paper presents an adaptive periodic-disturbance observer (APDO)-based composite control scheme to attain accurate velocity-tracking control for the single gimbal control moment gyro (SGCMG). Firstly, a modified periodic-disturbance observer (PDO) is proposed to estimate both the fundamental wave and harmonics of the rotor vibration. Secondly, to ensure the estimation accuracy under variable rotor speed, an APDO is proposed by combining an adaptive frequency estimator with the modified PDO. Integrating with the PI controller, the proposed APDO-based composite control scheme can effectively reduce the influence of rotor vibration, friction, and parameter uncertainties, thereby improving control accuracy. Furthermore, performance and stability analyses show that the observer can achieve accurate estimation under arbitrary initial conditions. Finally, numerical and hardware-in-the-loop simulation results are given to demonstrate the robustness and effectiveness of the proposed scheme. • Velocity control for SGCMG gimbal servo with multiple disturbances is considered. • An adaptive periodic-disturbance observer-based composite controller is proposed. • Known information of the rotor vibration is utilized to achieve accurate estimation. • An adaptive frequency estimator is applied to accommodate the frequency change. • Numerical and hardware-in-the-loop simulations show the robustness and effectiveness. [ABSTRACT FROM AUTHOR]

Reusable launch vehicles (RLVs) offer advantages such as low cost and high efficiency, yet they still face challenges related to real-time precise control and reliability enhancement. To address these issues, this paper presents a fixed-time attitude control method designed for RLVs, incorporating a reliability-based control allocation scheme. Initially, a fixed-time radial basis function neural network (RBFNN) disturbance observer is introduced to estimate disturbances rapidly and accurately. Subsequently, a control method integrating non-singular terminal sliding mode control (NTSMC) with a saturation compensator is proposed to achieve real-time and precise angle tracking. Furthermore, a reliability-based control allocation scheme is employed to enhance the reliability of the attitude control system. Finally, simulation analysis is conducted to validate the effectiveness of the proposed control scheme. • A reliability model for RLVs actuators is established. • A fixed-time RBFNN observer for disturbance estimation is proposed. • A fixed-time control using NTSMC and anti-windup compensator is developed. • A reliability-based control allocation is introduced to enhance reliability. [ABSTRACT FROM AUTHOR]

Secure guidance for missiles against cyber-attacks is an interesting topic of both theoretical and practical importance, but so far few results are available. In this paper, two multivariable secure guidance laws are proposed for precise strikes interceptors with cyber-attacks in guidance commands. Different engagement scenarios are studied in three-dimensional space. Against highly maneuvering targets, the proposed secure guidance law can guarantee some states related to the line-of-sight (LOS) angular rates to converge to zero within finite time, where the cyber-attacks are indirectly estimated and compensated with the aid of an attack observer. Moreover, against non-maneuvering targets with impact angle constraints, the proposed secure guidance law is designed based on the backstepping technique, where the cyber-attacks are directly estimated and compensated. Particularly, prescribed performance functions are introduced in the second guidance law to flexibly determine the convergence rates of the LOS angles. Numerical simulations are performed to illustrate the effectiveness of the proposed schemes. [ABSTRACT FROM AUTHOR]

The detection and compensation of attacks are crucial for UAV safety. This paper focuses on the case where the desired trajectory sent by ground control station (GCS) is attacked. Based on the analysis of the attack transmission mechanism, an integrated scheme of attack detection and compensation is presented. The attack detection mechanism is established based on the trajectory tracking error and state estimation error. In addition, the proposed scheme can not only detect attacks but also distinguish attacks from unknown abrupt disturbances. In the proposed scheme, attack observer (AO) and learning observer (LO) are developed to address the coupling problem of additive and multiplicative attacks. Finally, the effectiveness of the proposed scheme is validated by both simulation and experimental tests. [ABSTRACT FROM AUTHOR]