Sanjoy Mondal

This paper proposes a novel Adaptive Nonsingular Fixed-Time Path Following Control scheme for underactuated unmanned surface vehicles navigating under unknown uncertainties, environmental disturbances, and asymmetric input saturation constraints. The main contribution is the integration of a Fixed-Time Line-of-Sight guidance law with a homogeneity-based Adaptive Full-order Integral Terminal Sliding Mode control framework to achieve robust fixed-time path-following performance. Unlike conventional Line-of-Sight guidance methods with fixed or empirically selected look-ahead distances, the proposed Fixed-Time Line-of-Sight guidance law incorporates adaptive sideslip compensation and a dynamically adjusted look-ahead distance based on real-time cross-track error, enabling rapid and accurate heading correction under time-varying disturbances. Furthermore, a novel variable-exponent Adaptive Full-order Integral Terminal Sliding Mode controller is developed to guarantee nonsingular fixed-time convergence while simultaneously ensuring accurate tracking of both the desired heading angle and yaw rate. An adaptive gain mechanism is introduced to estimate and compensate unknown uncertainties online, eliminating the requirement for conservative prior bounds and mitigating control-gain overestimation. To address practical implementation issues, an asymmetric saturation function is incorporated directly into the control design to explicitly account for actuator limitations. Compared with existing fixed-time and finite-time path-following approaches, the proposed method simultaneously addresses adaptive sideslip compensation, fixed-time convergence, uncertainty rejection, singularity avoidance, second-order heading dynamics tracking, and asymmetric actuator saturation within a unified framework. A homogeneity-based variable-exponent Lyapunov analysis is developed to rigorously establish Fixed-Time Stability of the closed-loop system. Comparative simulation studies demonstrate that the proposed Adaptive Nonsingular Fixed-Time Path Following Control scheme achieves superior path-following accuracy, robustness, and disturbance-rejection capability compared with existing benchmark methods under constrained and uncertain marine environments.

This paper uses a fixed-time (FxT) dynamic event-triggered control(DETC) framework to study distributed multi leader-follower multi-group consensus for multi-agent systems(MASs) under disturbances. A normalized state-dependent variable-exponent (SDVE) design, which avoids the conservative tuning associated with constant-exponent techniques and modifies the convergence rate online in accordance with the system evolution, enforces FxT convergence. To improve resilience against matching uncertainties and external perturbations, a variable-exponent super-twisting algorithm (VSTA) is devised on nonlinear sliding manifolds. In order to facilitate simultaneous intra-group agreement and inter-group coordination while tracking different leader trajectories, agents are divided into several groups and communicate over a complex-valued communication graph. The FxT control architecture incorporates a DETC mechanism that ensures consensus without constant information transmission, hence reducing communication overhead. By establishing a positive infimum of the inter-event intervals and guaranteeing global FxT group consensus using just local information, the suggested technique eliminates Zeno behavior. Comparative numerical studies with conventional sliding mode and event-triggered approaches demonstrate significant communication savings, enhanced resilience, faster convergence, and a substantial reduction in chattering.

An event-triggered nonsingular fixed-time sliding mode control (ET-NFxT-SMC) scheme is developed for trajectory tracking of quadrotor unmanned aerial vehicles (QUAVs). The proposed controller employs a state-dependent variable exponent (SDVE) framework to ensure fixed-time stability (FxTS). Unlike constant-exponent methods, it adapts the convergence rate dynamically to the system state, offering a simplified structure with reduced computational complexity. The proposed approach addresses altitude and attitude tracking problems in the presence of external disturbances and system uncertainties. An event-triggering mechanism is integrated to significantly reduce unnecessary control updates by up to 52% without compromising stability. Thus, computational load and signal transmission bandwidth are further reduced, while maintaining robust performance. The Lyapunov-based analysis ensures FxT convergence and confirms a positive lower bound on inter-event times, thus avoiding Zeno behavior. Simulation results demonstrate that the proposed controller achieves accurate and robust trajectory tracking with fewer control updates, leading to improved resource efficiency and practical implementation feasibility.

The problem of altitude and attitude tracking problem of nonlinear quad rotor type unmanned aerial vehicles (QUAV) is addressed by dynamic event-triggered based nonsingular terminal sliding mode control (TSMC) scheme. In order to achieve fast reaching of desired trajectories in presence of unknown disturbances and uncertainties, nonsingular terminal sliding surface is defined. Moreover, the superior performance is achieved with limited resource of computation and communication channel band width by using dynamic event-triggered (DET) strategy. Fast convergence of tracking errors for the proposed control strategy is ensured via Lyapunov stability. The Zeno phenomena is proved to be excluded through precise analysis for the proposed dynamic event-triggered based TSMC scheme. The effectiveness of DET mechanism is examined over static and time triggered implementation of TSMC law for QUAV system.