Inertia Uncertainties Research Articles

Fault-Tolerant Attitude Stabilization for Spacecraft With Low-Frequency Actuator Updates: An Integral-Type Event-Triggered Approach

This article investigates the attitude stabilization control problem with low-frequency communication to actuators in the framework of sampled-data control. A novel event-triggered sampling control policy is proposed by employing an integral-type triggering function where the determination of all sampling times is by judging the properties of this function including the integration of measurement errors. Using the Lyapunov-based approach, we show that the stability of the closed-loop system can be guaranteed in the presence of external disturbance, inertia uncertainty, and actuator fault. Compared with conventional attitude control policies, the proposed algorithm significantly reduces the data-rate requirement in updating the actuator while providing high reliability and accurate performance for attitude stabilization. Compared with the traditional event-triggered sampling, the proposed policy is no longer by judging the instantaneous state of measurement errors, which reduces the sampling frequency and does not increase the computational burden. Numerical simulations are conducted to show a decent performance of the algorithm.

Imperfect Roll Arrangement Compensation Control based on Neural Network for Web Handling Systems

The speed and tension control problem of a web handling system is investigated in this paper. From the system equations of motion, we developed a backstepping-sliding mode control for web speed and tension regulation tasks. It is obvious that the designed control depends heavily on roll inertia information. Dissimilar to other researches that were based on the assumptions of rolls with perfect cylindrical form with the rotating shafts of the rolls considered properly aligned, the novelty of this paper is the presentation of a neural network to compensate the effects of imperfect roll arrangement. The neural network design is based on the Radial Basis Function (RBF) network estimating the uncertainty of roll inertia. The information on estimated inertia is fed into a backstepping-sliding mode controller that ensures tension and velocity tracking. The control design is presented in a systematical approach. Closed loop system stability is proven mathematically. The tracking performance is shown through several simulation scenarios.

Fixed-time control for high-precision attitude stabilization of flexible spacecraft

This is a study of adaptive constraint attitude control for a flexible spacecraft in the presence of inertia uncertainties, unknown disturbance, actuator saturation and faults. The proposed controller is designed by incorporating a Prescribed Performance Control (PPC) and fixed-time sliding mode control. First, a novel Nonsingular Fast Fixed-time Sliding Surface (NFFTSS) is introduced. Not only is the settling time independent of initial conditions, but also it is shorter than existing fixed-time attitude controls. Second, different from the conventional complex PPCs in the literature, a simple structure attitude controller is proposed to satisfy the transient and steady-state performance is proposed through a novel log-type PPC. An inherently continuous adaptive switching control is then presented in order to avoid the a priori not to require accurate information of the fault occurrence. Numerical simulations demonstrate that the proposed controller successfully accomplishes attitude control with high attitude pointing accuracy and stability.

Disturbance observer-based attitude stabilization for rigid spacecraft with input MRCs

This paper studies the problem of attitude stabilization for a rigid spacecraft subject to external disturbances, time-varying inertia uncertainties, and input magnitude and rate constraints (MRCs). By analyzing the influence of inertia uncertainties, the reconstruction of lumped disturbances is accomplished to facilitate the controller design. Then, a disturbance observer is designed, based on which, a simple state feedback control strategy including estimation of lumped disturbances is proposed. By choosing new state variables using attitude information and estimation errors, an augmented plant is constructed. Using standard Lyapunov stability analysis, which shows that all states are uniformly ultimately bounded, sufficient conditions for the existence of the disturbance observer and controller are given based on linear matrix inequalities (LMIs). It is worth pointing out that the observer and controller gains are obtained simultaneously. It is shown that the control scheme developed is not only robust against external disturbances and unknown time-varying inertia uncertainties, but also able to steer the attitude control performance and estimation errors of lumped disturbances. Numerical simulations are performed to demonstrate the effectiveness of the proposed control strategy.

Robust fixed-time attitude stabilization control of flexible spacecraft with actuator uncertainty

A robust fixed-time control framework is presented to stabilize flexible spacecraft’s attitude system with external disturbance, uncertain parameters of inertia, and actuator uncertainty. As a stepping stone, a nonlinear system having faster fixed-time convergence property is preliminarily proposed by introducing a time-varying gain into the conventional fixed-time stability method. This gain improves the convergence rate. Then, a fixed-time observer is proposed to estimate the uncertain torque induced by disturbance, uncertain parameters of inertia, and actuator uncertainty. Fixed-time stability is ensured for the estimation error. Using this estimated knowledge and the full-states’ measurements, a nonsingular terminal sliding controller is finally synthesized. This is achieved via a nonsingular and faster terminal sliding surface with faster convergence rate. The closed-loop attitude stabilization system is proved to be fixed-time stable with the convergence time independent of initial states. The attitude stabilization performance is robust to disturbance and uncertainties in inertia and actuators. Simulation results are also shown to validate the attitude stabilization performance of this control approach.

Reaction wheel fault‐tolerant finite‐time control for spacecraft attitude tracking without unwinding

SummaryThis article proposes fault‐tolerant finite‐time attitude tracking control of a rigid spacecraft actuated by four reaction wheels without unwinding problem in the presence of external disturbances, uncertain inertia parameter, and actuator faults. First, a novel antiunwinding finite‐time attitude tracking control law is derived with a designed control signal which works within a known actuator‐magnitude constraint using a continuous nonsingular fast terminal sliding mode (NFTSM) concept. Second, a finite‐time disturbance observer (FTDO) is introduced to estimate a lumped disturbance due to external disturbances, uncertain inertia parameter, actuator faults, and input saturation. Third, a composite controller is developed which consists of a feedback control based on the continuous NFTSM method and compensation term based on the FTDO. The global finite‐time stability is proved using Lyapunov stability theory. Moreover, the singularity and unwinding phenomenon are avoided. Simulation results are conducted under actuator constraints in the presence of external disturbances, inertia uncertainty, and actuator faults and results are illustrated to show the effectiveness of the proposed method. In addition, to show the superiority of the proposed control method over the recently reported control methods, comparative analysis is also presented.

Distributed Finite-Time Coordinated Attitude Tracking Control for Multiple Spacecraft with Actuator Saturation

For multi-spacecraft with actuator saturation, inertia uncertainties and external disturbances, a distributed finite-time coordinated attitude tracking control problem for the spacecraft with the communication topology containing fewer information paths is investigated. Aiming at reducing the communication path, a class of distributed finite-time state observers is designed. To speed up the convergence rate of the multiple spacecraft system, a fast nonsingular terminal sliding mode function is proposed. Moreover, an adaptive control term is proposed to suppress the impact of the external state-dependent disturbances and unknown time-varying inertia uncertainties. Further considering the actuator saturation owing to its physical limitations, a saturation function is designed. With the distributed finite-time observers, the fast nonsingular terminal sliding mode function, the adaptive update law and the saturation function, a distributed finite-time coordinated attitude tracking saturation controller is designed. Using the proposed controller, the follower can synchronize with the common leader with time-varying trajectory in finite time. Simulation results demonstrate the effectiveness of the designed controller.

Fixed‐time attitude tracking control for rigid spacecraft

This study addresses the fixed-time attitude tracking for rigid spacecraft with inertia uncertainties and external disturbances. Firstly, a new fixed-time sliding surface based on the bi-limit homogeneous theory is proposed. Secondly, a non-singular sliding mode control is designed to solve the robust fixed-time attitude tracking problem. It is proved that the proposed control can ensure that the sliding surface and attitude tracking errors converge to zero within fixed time. The appealing features of the proposed control are exact fixed-time tracking stability with fast convergence, high precision, strong robustness and easy implementation. Simulations verify the effectiveness and improved performance of the proposed approach.

Robust adaptive attitude control for non-rigid spacecraft with quantized control input

In this paper, an adaptive backstepping control scheme is proposed for attitude tracking of non-rigid spacecraft in the presence of input quantization, inertial uncertainty and external disturbance. The control signal for each actuator is quantized by sector-bounded quantizers, including the logarithmic quantizer and the hysteresis quantizer. By describing the impact of quantization in a new affine model and introducing a smooth function and a novel form of the control signal, the influence caused by input quantization and external disturbance is properly compensated for. Moreover, with the aid of the adaptive control technique, our approach can achieve attitude tracking without the explicit knowledge of inertial parameters. Unlike existing attitude control schemes for spacecraft, in this paper, the quantization parameters can be unknown, and the bounds of inertial parameters and disturbance are also not needed. In addition to proving the stability of the closed-loop system, the relationship between the control performance and design parameters is analyzed. Simulation results are presented to illustrate the effectiveness of the proposed scheme.

Quantized Attitude Control of Rigid Spacecraft without Unwinding

Advanced spacecrafts like fractionated spacecrafts are developed using independent modules that interact with each other through a wireless communication channel. The designing of an attitude controller of such spacecrafts requires to abide by the constraints on communication resources. Therefore, in this paper, a logarithmic quantizer is employed for the attitude regulation of rigid spacecraft under limited utilization of the wireless network. The given spacecraft has inertial uncertainties and external disturbances. Furthermore, the quaternion based kinematics attitude representation suffers from the problem of unwinding due to multiple equilibrium points. Thus, under the action of the proposed anti-unwinding controller, the closed-loop system states converge to the uniformly ultimate bounds while attenuating the lumped disturbances and avoiding the unwinding phenomenon. The simulation analysis and the comparative study with multiple initial conditions illustrate the superior performance of the proposed control technique.

Agile Spacecraft Attitude Control: an Incremental Nonlinear Dynamic Inversion Approach

This paper presents an agile and robust spacecraft attitude tracking controller using the recently reformulated incremental nonlinear dynamic inversion (INDI). INDI is a combined model- and sensor-based control approach that only requires a control effectiveness model and measurements of the state and some of its derivatives, making a reduced dependency on exact system dynamics knowledge. The reformulated INDI allows a non-cascaded dynamic inversion control in terms of Modified Rodrigues Parameters (MRPs) where scheduling of the time-varying control effectiveness is done analytically. This way, the controller is only sensitive to parametric uncertainty of the augmented spacecraft inertia and its wheelset alignment. Moreover, we draw some parallels to time-delay control (TDC) —more familiar in the robotics community— which have been shown to be equivalent to the incremental formulation of proportional-integral-derivative (PID) control for second order nonlinear systems in controller canonical form. Simulation experiments for this particular problem demonstrate that INDI has similar nominal performance as TDC/PID control, but superior robust performance and stability.

Neural-Network-Based Adaptive Event-triggered Control for Spacecraft Attitude Tracking.

The problem of attitude tracking control for spacecraft with limited communication rate is addressed in this article. To reduce the communication burden, an adaptive event-triggered control scheme is proposed. In the control scheme, only the sampling states at the event-triggering instants are sent to the control module, which can considerably decrease the data transmission rate. To address the inertia uncertainties and external disturbances, a radial basis function neural network (NN) is introduced. The bound of the uncertainties and disturbances is estimated for the proposed control scheme, which can simplify the NN and reduce the computation. Since the event-triggered error signal is discontinuous due to the event-triggered mechanism, the closed-loop system is formulated as an impulsive dynamical system to obtain the stability properties of the system. Finally, simulation results are given to demonstrate the effectiveness of the proposed control scheme.

Fixed-Time Fault-Tolerant Attitude Tracking Control for Rigid Spacecraft

Abstract This paper addresses the fixed-time attitude tracking problem of rigid spacecraft with inertial uncertainties, external disturbances, and partial loss of actuator effectiveness faults. A new fixed-time terminal sliding surface is proposed and a singularity-free fixed-time fault-tolerant sliding mode control (FTSMC) is designed. It is proved that the proposed FTSMC can ensure that the attitude tracking errors converge to an arbitrary small bound centered on the equilibrium point within fixed time and then go to the equilibrium point asymptotically. The appealing features of the proposed control are fixed-time tracking stability featuring fast convergence, high precision, and strong robustness. Simulations verify the effectiveness of the proposed approach.

Immersion and invariance adaptive tracking control for robot manipulators with a novel modified scaling factor design

SummaryThe robot manipulators' tracking control problem in the presence of inertia uncertainties is addressed in this paper, and a novel dynamic scaling–based immersion and invariance (I&I) adaptive tracking controller is utilized to stabilize the proposed system. By virtue of the reconstruction method of the parameter regression matrix, this paper provides a new perspective on how to overcome the integrability obstacle typically arising in the I&I controller design through dynamic scaling and presents a new controller design method. What is more, a novel modified scaling factor is proposed as well so that the controller can be implemented without the prior knowledge of the inertia matrix's lower bound, and only the saturation function involving the scaling factor is included in the feedback gains. Finally, the numerical simulations show the validity of the proposed controller.

Event-triggered attitude tracking for rigid spacecraft

This study aims to investigate the problem of attitude control for a spacecraft with inertial uncertainties, external disturbances, and communication restrictions. An event-triggered active disturbance rejection control approach is proposed for attitude tracking of the spacecraft. An event-triggered mechanism is introduced together with an extended state observer to jointly monitor the system states and total disturbances. The observation error is proved to be uniformly bounded. Based on the proposed control scheme, the integrated tracking system is shown to be asymptotically stable, implying successful attitude tracking of the spacecraft for the desired motion. Numerical results illustrate the effectiveness of the control strategy in achieving satisfactory tracking performance with a reduced data-transmission cost.

Inertia‐free attitude stabilization for flexible spacecraft with active vibration suppression

SummaryThis paper addresses the inertia‐free attitude control problem for flexible spacecraft in the presence of inertia uncertainties, external disturbances, actuator faults, measurement errors, and input magnitude and rate constraints (MRCs). By analyzing the influence of external disturbances, faulty signals, and actual inertial matrix, a lumped disturbance is reconstructed to facilitate the controller design. Then, a new intermediate observer is developed to estimate the attitude and modal information and the lumped disturbance. The Lyapunov stability analysis shows that the developed controller can achieve the objectives of the attitude stabilization and vibration suppression with input MRCs. Finally, numerical simulations are performed to demonstrate the effectiveness and superiority of the proposed control method.

Finite-time attitude maneuvering and vibration suppression of flexible spacecraft

The finite-time attitude maneuvering control and vibration suppression for the flexible spacecraft with external disturbances, inertia uncertainties and input saturation are investigated in this paper. Firstly, the input shaping technique is applied to suppress most of the vibration caused by flexible appendages. Then, for the nominal attitude control system, a multivariable continuous sliding mode controller is applied to guarantee the finite-time convergence. Next, unlike the conventional discontinuous design of integral sliding mode, a continuous compensated controller with modified multivariable adaptive twisting algorithm is proposed to reject the lumped uncertainty, including disturbances, uncertainties, saturation and residual vibration. The controller can realize finite time convergence and the chattering suppression, while there’s no need for the priori knowledge of the lumped uncertainty. A rigorous proof of the finite time stability of the closed-loop system is derived by the Lyapunov method. Finally, the efficiency of the proposed method is illustrated by numerical simulations.

Fault-tolerant attitude tracking control of combined spacecraft with reaction wheels under prescribed performance

Capture and control of a failed spacecraft can be achieved by a space manipulator installed in a service spacecraft. After this target has been captured, the combined spacecraft must be controlled in a prescribed way. The attitude attacking control of the combined spacecraft system is one major challenge since the mass properties of the whole spacecraft system and configuration matrix of the reaction wheels change, especially when actuator fault occurs. In this paper, a nonlinear disturbance-observer-based fault-tolerant attitude control scheme is developed for the combined spacecraft with prescribed performance. Firstly, an approach is given to reconstruct the attitude tracking dynamics of the combined spacecraft with reaction wheels. Then, a fault-tolerant controller, based on dynamic surface method and nonlinear extended state observer, is developed whereby performance in the light of convergence time, stability and accuracy with inertia uncertainty, actuator saturation and external disturbance can be prescribed. Finally, comparative simulations in both actuator faults and actuator fault-free cases are conducted to show the superiority of the developed attitude tracking control method.

Adaptive Fixed-Time Attitude Tracking Control for Rigid Spacecraft With Actuator Faults

This paper investigates fixed-time attitude tracking maneuver of rigid spacecraft in the presence of actuator faults, external disturbances, and inertia uncertainties. First, a fast finite-time stable system is investigated in the sense of fixed-time concept. Then, a nonlinear observer is designed to estimate the information of the lumped uncertainties, and this observer, integral sliding mode and geometric homogeneity are used to formulate one attitude controller, which can guarantee attitude tracking errors can be stabilized to the origin. Second, another adaptive controller is presented to steer attitude tracking errors to the equilibrium point. Lyapunov techniques are implemented to ensure the fixed-time stability of the closed-loop system. Finally, numerical simulations are carried out to demonstrate the performance of the proposed controllers.

High-Precision Attitude Tracking Control of Space Manipulator System Under Multiple Disturbances

Precise attitude control of space manipulators plays an important role in advanced on-orbit assembly tasks. The vibration of flexible appendage and inertial uncertainties encountered in the operating process, however, may cause attitude error or even safety threats to the space manipulator system. In this article, a high-precision attitude control scheme of a space manipulator system is designed via a combination of disturbance observer (DO), prescribed performance-based H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">∞</sub> control, and iterative learning control (ILC) techniques. The proposed control scheme consists of three portions: 1) a DO that estimates the vibration disturbance caused by flexible appendage of base satellite; 2) a robust H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">∞</sub> controller with prescribed performance to attenuate the inertial uncertainties resulting from capture of an unknown object; and 3) an ILC for improving the transient and steady-state process in the presence of a repetitive on-orbit assembly task. This novel control scheme can not only handle the flexible vibration and inertial uncertainty of the space manipulator but also achieve satisfactory tracking performance. Both simulation and experimental results confirm the superiority of the proposed control strategy.