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Author

Julius A. Marshall

Other affiliations: University of Oklahoma
Bio: Julius A. Marshall is an academic researcher from Virginia Tech. The author has contributed to research in topics: Adaptive control & Reference model. The author has an hindex of 2, co-authored 6 publications receiving 14 citations. Previous affiliations of Julius A. Marshall include University of Oklahoma.

Papers
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Journal ArticleDOI
TL;DR: This article presents an innovative control architecture for tilt-rotor quadcopters with H-configuration transporting unknown, sling payloads that employs barrier Lyapunov functions and a novel robust model reference adaptive control law to guarantee a priori user-defined constraints on both the trajectory tracking error and the control input, despite poor information on the aircraft's inertial properties and the presence of unknown, unsteady payloads.
Abstract: This article presents an innovative control architecture for tilt-rotor quadcopters with H-configuration transporting unknown, sling payloads. This control architecture leverages on a thorough analysis of the aircraft's equation of motion, which reveals gyroscopic effects that were not fully characterized and were disregarded while synthesizing control algorithms in prior publications. Furthermore, the proposed control architecture employs barrier Lyapunov functions and a novel robust model reference adaptive control law to guarantee a priori user-defined constraints on both the trajectory tracking error and the control input, despite poor information on the aircraft's inertial properties and the presence of unknown, unsteady payloads. Flight tests involving a quadcopter pulling an unmodeled cart by means of a thin rope of unknown length, which is slack at the beginning of the mission, verify the effectiveness of the theoretical results.

23 citations

Journal ArticleDOI
TL;DR: In this paper, a user-defined rate of convergence for nonlinear dynamical systems affected by matched and parametric uncertainties is proposed to constrain both the closed-loop system's trajectory tracking error and the control input at all times within user defined bounds.
Abstract: In classical model reference adaptive control (MRAC), the adaptive rates must be tuned to meet multiple competing objectives. Large adaptive rates guarantee rapid convergence of the trajectory tracking error to zero. However, large adaptive rates may also induce saturation of the actuators and excessive overshoots of the closed-loop system’s trajectory tracking error. Conversely, low adaptive rates may produce unsatisfactory trajectory tracking performances. To overcome these limitations, in the classical MRAC framework, the adaptive rates must be tuned through an iterative process. Alternative approaches require to modify the plant’s reference model or the reference command input. This paper presents the first MRAC laws for nonlinear dynamical systems affected by matched and parametric uncertainties that constrain both the closed-loop system’s trajectory tracking error and the control input at all times within user-defined bounds, and enforce a user-defined rate of convergence on the trajectory tracking error. By applying the proposed MRAC laws, the adaptive rates can be set arbitrarily large and both the plant’s reference model and the reference command input can be chosen arbitrarily. The user-defined rate of convergence of the closed-loop plant’s trajectory is enforced by introducing a user-defined auxiliary reference model, which converges to the trajectory tracking error obtained by applying the classical MRAC laws before its transient dynamics has decayed, and steering the trajectory tracking error to the auxiliary reference model at a rate of convergence that is higher than the rate of convergence of the plant’s reference model. The ability of the proposed MRAC laws to prescribe the performance of the closed-loop system’s trajectory tracking error and control input is guaranteed by barrier Lyapunov functions. Numerical simulations illustrate both the applicability of our theoretical results and their effectiveness compared to other techniques such as prescribed performance control, which allows to constrain both the rate of convergence and the maximum overshoot on the trajectory tracking error of uncertain systems.

12 citations

Journal ArticleDOI
TL;DR: The effectiveness of the proposed control architecture is proven in two alternative frameworks, that is, analyzing Caratheodory and Filippov solutions of discontinuous differential equations, to verify the applicability of the theoretical results to problems of practical interest.
Abstract: This paper presents an adaptive control law for unknown nonlinear switched plants that must follow the trajectory of user-defined linear switched reference models. The effectiveness of the proposed control architecture is proven in two alternative frameworks, that is, analyzing Caratheodory and Filippov solutions of discontinuous differential equations. Numerical and experimental data verify the applicability of the theoretical results to problems of practical interest. The proposed numerical simulation involves the design of a model reference adaptive control law to regulate the roll dynamics of a reconfigurable delta-wing aircraft. The proposed flight tests involve an aerial robot tasked with autonomously mounting a camera of unknown inertial properties to a vertical surface.

8 citations

Journal ArticleDOI
TL;DR: In this article, the authors present a holistic perspective on the state-of-the-art in the design of guidance, navigation, and control systems for autonomous multi-rotor small unmanned aerial systems (sUAS).

7 citations

Proceedings ArticleDOI
10 Jul 2019
TL;DR: This analysis is the first to show a nonlinear effect in the vehicle's rotational dynamics due to the fact that not all propellers of a tilt-rotor are aligned to one of the vehicles's principal axes.
Abstract: This paper analyzes the dynamics of tilt-rotor quadcopters with H-configuration and synthesizes a control system for these vehicles. Our analysis is the first to show a nonlinear effect in the vehicle's rotational dynamics due to the fact that not all propellers of a tilt-rotor are aligned to one of the vehicle's principal axes. The proposed control system relies on an original robust model reference adaptive control law to guarantee user-defined constraints on both the trajectory tracking error and the adaptive gains at all despite parametric, matched, and unmatched uncertainties due to unknown external disturbances and dangling payloads.

6 citations


Cited by
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Journal ArticleDOI
TL;DR: This is the first study to perform simultaneous trajectory tracking and aerial grasping tasks while ensuring closed-loop stability in the presence of operational constraints, and the results demonstrate the satisfactory performance of the proposed control scheme for robust trajectory Tracking and aerial manipulation missions at an acceptable computational cost.

24 citations

Journal ArticleDOI
05 Jan 2022-Robotics
TL;DR: This research explores the invertible gait for the tiltrotor and applies the feedback linearization to stabilize the attitude and the altitude and introduces the novel concept "UAV gait" to restrict the tilting angles.

11 citations

Journal ArticleDOI
TL;DR: In this paper , a non-fragile memory state feedback controller is chosen to ensure the globally uniformly exponential stability condition for proposed nonlinear systems through the linear matrix inequalities (LMI) approach.

8 citations

Journal ArticleDOI
TL;DR: The effectiveness of the proposed control architecture is proven in two alternative frameworks, that is, analyzing Caratheodory and Filippov solutions of discontinuous differential equations, to verify the applicability of the theoretical results to problems of practical interest.
Abstract: This paper presents an adaptive control law for unknown nonlinear switched plants that must follow the trajectory of user-defined linear switched reference models. The effectiveness of the proposed control architecture is proven in two alternative frameworks, that is, analyzing Caratheodory and Filippov solutions of discontinuous differential equations. Numerical and experimental data verify the applicability of the theoretical results to problems of practical interest. The proposed numerical simulation involves the design of a model reference adaptive control law to regulate the roll dynamics of a reconfigurable delta-wing aircraft. The proposed flight tests involve an aerial robot tasked with autonomously mounting a camera of unknown inertial properties to a vertical surface.

8 citations

Journal ArticleDOI
TL;DR: In this article, the authors present a holistic perspective on the state-of-the-art in the design of guidance, navigation, and control systems for autonomous multi-rotor small unmanned aerial systems (sUAS).

7 citations