This paper addresses attitude tracking and vibration suppression problems during the flexible spacecraft maneuvers under the influence of system parametric uncertainties, external disturbances, and actuator nonlinear saturation without utilizing intelligent materials or smart vibration suppression actuators. Specifically, we develop a dual observer-based backstepping (DOB-BST) controller that employs a recursive control design to devise observers to estimate and attenuate the effect of perturbations in spacecraft attitude kinematics and dynamics. Moreover, the proposed DOB-BST controller uses an input compensator to mitigate the adverse impacts of saturation nonlinearity in a closed-loop system. The proposed control structure offers finite time convergence of closed-loop system states to a small neighborhood of zero. In addition, we give system state convergence regions and derive explicit tuning conditions to downsize the convergence region using Lyapunov stability analysis. Finally, the simulation experiment results confirm the performance of the proposed control algorithm despite the multiple system constraints.

We present a continuous attitude-tracking control strategy for energy-efficient real-time torque selection in autonomous aerial systems (AAS). The conventional unit-quaternion-based controllers may induce unwanted extra rotations due to the double-cover property of quaternions, which makes them inefficient in terms of time and energy. This paper presents an energy-efficient framework for attitude-tracking control of AAS in the presence of external disturbances and parameter uncertainties. We introduce a scalar error function to construct an associated error vector that regulates attitude convergence. The error vector serves as the basis for controller design when both the unit-quaternion equilibria are stable. The proposed energy-efficient framework-based controller inherently avoids unwanted rotations during attitude maneuvers and ensures almost global orientation tracking. Compared to conventional unit-quaternion-based controllers, the proposed energy-efficient framework is 71% more efficient in terms of energy. The simulation results show satisfactory performance of the proposed energy-efficient framework.

Maritime rescue mission presents a substantial operational challenge due to the unpredictable and challenging environment, inaccessibility, and scarcity of skilled manpower. This paper proposes a distributed task allocation method for the autonomous deployment of a multi-fixed-wing UAV (FW-UAV) system for rapid resource distribution in the Deep Sea. A dynamic distributed collaborative task allocation (DCTA) algorithm is developed using a distributed adaptive genetic algorithm (DAGA) for optimal resource assignment. The proposed DAGA-based DCTA framework facilitates cooperative decision-making and decentralized task allocation, confirming UAV agents reach a consensus on synchronized rescue execution with rapid arrival and optimal spatial task distribution. We conduct simulation experiments to demonstrate the robust and effective performance of the proposed DAGA-based DCTA method in terms of mission success rates, computational efficiency, and uniform resource allocation for the time-critical rescue of moving maritime distressed vessels (MMDVs).

Accurate, reliable, and fast trajectory tracking in the presence of system uncertainties and external disturbances that vary with time is essential for robotic manipulator operating in adverse environments. Unmodeled dynamics and perturbations can severely degrade closed-loop performance and interfere with task execution. This paper introduces a predefined-time trajectory tracking control strategy for robotic manipulators with time-varying parameter uncertainties and unknown external perturbations. The objective is to design a robust controller that performs tracking tasks in user-defined time frames. First, a nonlinear sliding manifold is constructed, such that the system states reach the sliding mode surface within a predefined time, regardless of initial conditions. Then, a robust controller is developed to ensure the convergence of the system state errors to a small neighborhood around the origin within a user-specified time window. The proposed control framework guarantees fast and precise convergence. Numerical simulations performed on a robotic manipulator are presented to demonstrate the effectiveness and robustness of the proposed control strategy in terms of tracking accuracy, convergence rate, and disturbance rejection capability.

This paper presents an active fault-tolerant control (FTC) framework for aerial vehicles operating under system uncertainties, external disturbances, and actuator faults or failures. Specifically, we propose a nonlinear integral sliding mode-based fault-tolerant control allocation scheme to address actuator faults and failures in an octocopter system. The goal is to perform trajectory tracking control and ensure system stability under practical operating conditions while preserving nominal closed-loop performance during fault scenarios. A baseline controller is first designed using a backstepping approach and combined with a nonlinear integral sliding mode control law to achieve nominal stability. To manage actuator degradation, a control allocation strategy is developed to redistribute control efforts among healthy redundant actuators based on real-time estimates of actuator effectiveness. Key features of the proposed FTC framework include its ability to handle faults and failures online while maintaining robustness against system perturbations. The simulation results demonstrate the effectiveness of the proposed BT-ISMC-based FTC method in sustaining performance under fault and failure conditions.

This work proposes a reliable control scheme to attain the precise tracking control of multirotor unmanned aerial vehicle systems used for smart agriculture. The nonlinear mathematical model of a co-axial octorotor system equipped with a spraying mechanism is first established to contain the time-varying inertial coefficients and varying payload effects. Then an adaptive backstepping controller scheme is proposed to attain the desired attitude and position tracking. To ensure robustness against parameter uncertainty and external disturbances, a high-order integral sliding mode controller is integrated with the adaptive backstepping controller. Numerical simulations are carried out in variable payload conditions to demonstrate the effectiveness of the proposed approach.

This paper describes a new fault-tolerant control technique for over-actuated uncertain linear systems that compensates for actuator faults and failures using an output integral sliding mode-based control allocation strategy. An observer-based fault estimation unit is first proposed to estimate the system states and the actuator’s effectiveness level. Based on the estimated state’s information, a nominal virtual control law is created to achieve the desired specification of the perturbed system. A nonlinear output integral sliding manifold is incorporated with the nominal virtual control law that provides resilience to the closed-loop system against the uncertainty caused by the actuator’s faults and failure, states estimation error, and fault estimation error. Finally, depending on anticipated actuator efficacy from the fault estimation unit, the control allocation reroutes the virtual control input signals among the redundant actuators. A small-gain theorem is used to demonstrate the augmented closed-loop system stability. The observer and controller gains are synthesized using the linear matrix inequality technique. Finally, simulations on an aircraft system are performed to verify the efficacy of the suggested FTC technique. Compared with the existing work, the proposed approach is better able to handle actuator redundancy in faulty conditions and cater to the fault estimation error up to a certain level.Note to Practitioners—The aim of this paper is to address the reliability issues of industrial systems that contain sufficient input redundancy and are particularly designed to tolerate the faults and failures issues during the system operation. Existing fault-tolerant control schemes based on control allocations have limitations in terms of effective utilization of actuator redundancy, handling of fault estimation error, and applicability of reconfigurable control law. In this paper, we developed a fault-tolerant control strategy that is capable of addressing all the aforementioned concerns. The output integral sliding mode control-based control allocation scheme, proposed in this paper, is applicable to the class of over-actuated systems. The reconfiguration of fault-tolerant control law based on the estimated states and fault information is capable to cover a wider class of faults and failures while maintaining robustness against the system dynamics and uncertainty. The control reconfiguration is equally applicable to the class of systems that contains both rank-deficient and in-deficient input distribution matrices. The proposed scheme assumed the bounded external disturbance, therefore in future work, the adaptive law will be incorporated with sliding mode controller and results will be extended to a generalized class of affine nonlinear systems.

Quaternion representation of spacecraft has double equilibrium points associated with it, which may cause unwinding phenomenon in attitude control if both equilibria are not treated as stable during control law design procedure. This paper presents anti-unwinding attitude tracking control of rigid body spacecraft in presence of external disturbance and model uncertainties. In pursuit of our goal, anti-unwinding attitude tracking control law using back-stepping technique (BT) is developed, in accomplice with sliding mode control (SMC). Sliding surface using initial value of scalar component of quaternion is formulated. Furthermore, system dynamics are transformed to facilitate application of observer for estimation of lumped uncertainties. Extended state observer (ESO) is employed to compensate for total system uncertainties. The proposed controller gives faster transient response. Furthermore, controller output is chattering free and smooth. In addition, proposed control law has superior disturbance rejection capabilities and is robust against model uncertainties. Stability analysis of closed loop system is performed using Lyapunovs theory and Barbalats lemma in finite time (FT). Numerical simulations are performed to show the efficiency of proposed control scheme.