Filiberto Munoz

Second order sliding mode controllers for altitude control of a quadrotor UAS

This article deals with the design and real-time implementation of three second order sliding mode controllers for the altitude tracking of a quadrotor aircraft. A comparative study based on the analysis of the tracking error was performed in order to determine the controller presenting the best performance in a real-time application at outdoors environments. The compared strategies were the Classical First Order Sliding Mode Controller, the Super Twisting Sliding Mode Controller, the Modified Super Twisting Sliding Mode Controller and the Nonsingular Terminal Super Twisting Sliding Mode Controller. The last three controllers are based on the second order sliding mode technique, and they ensure robustness with respect to modeling errors even under external disturbances while reducing the chattering phenomenon in comparison with first order sliding mode controllers. Lyapunov stability theory is used to prove convergence in finite time of the altitude tracking error in the different proposed control laws. In order to demonstrate the effectiveness of the proposed solutions, an extensive set of simulation and real-time experimental results are presented.

Implementation of leader-follower linear consensus algorithm for coordination of multiple aircrafts

In this paper, we consider the tracking problem for leader-follower multi-agent systems under a linear consensus protocol. Our main goal is to study the real-time behavior of the algorithm when applied to a group of four holonomic Unmanned Aircraft Systems (UAS). A comprehensive analysis of the linear consensus protocol theory is presented. In our approach, the linear model of the agents are obtained by using the step response methodology, then, the models are approximated to a standard second-order model representation. The leader-follower consensus algorithm is designed and implemented for the heading and the altitude dynamics of the group of UAS. In order to prove the effectiveness of the proposed consensus algorithm we have implemented it both in simulation as well as in real-time experiments. Our work concludes with future directions of our research, which will address the issues found during the real-time tests.

A UAS obstacle avoidance strategy based on spiral trajectory tracking

This article proposes a methodology for enabling Unmanned Aircraft Systems (UASs) to avoid obstacles. The strategy, which makes use of a Robust Exact Differentiation (RED), relies on spiral trajectory tracking maneuvers, and is based on a backstepping controller with disturbance compensation. The RED strategy has been adopted since it enables the exact estimation of disturbances from the first moment, a characteristic that may be useful for real-time UAS operations in environments with obstacles. Our research concentrates in one of the main components of a Sense and Avoid (SSA) system, specifically, conflict resolution, leaving as future work the sensing aspect. To demonstrate the performance of the proposed solution, we present a set of simulation results as well as a real-time experiment where a holonomic UAS makes use of the estimation and control strategy while evolving in an environment with obstacles.

Super Twisting vs Modified Super Twisting algorithm for altitude control of an Unmanned Aircraft System

This article proposes two control strategies to track a desired altitude of an Unmanned Aircraft System (UAS). These strategies are a Super-Twisting Sliding Mode Controller (Super Twisting-SMC) and a Modified Super-Twisting Sliding Mode Controller (Modified Super Twisting-SMC), both controllers are robusts and present a satisfactory effectiveness even under external disturbances. The Lyapunov Stability Theory is used to guarantee the asymptotic convergence of the altitude tracking error in both control laws. To demonstrate the performance of the proposed solutions, a set of simulation results and experimental results are presented. To carry out the experiments an holonomic quad-rotor UAS is used and their altitude is obtained by using a Motion Capture System. From the theoretical and experimental results it can be proved that the Modified Super Twisting-SMC presents a faster response than the Super Twisting-SMC.

Altitude control of an Unmanned Aircraft System using a Super-Twisting controller based on High Order Sliding Mode Observer

In this paper, the altitude tracking problem for an Unmanned Aircraft System (UAS) is considered under the assumption that the altitud velocity is unknown. Since in a practical implementation the employed sensors used to measure the altitude (Barometer and GPS) do not provide the altitude velocity. The proposed strategy was designed by using a Super-Twisting controller based on a High Order Sliding Mode Observer. A comprehensive stability analysis based on the Lyapunov Stability Theory guarantees the convergence of the tracking error in finite time. To demonstrate the performance of the proposed solution, a set of simulation results are presented.

Multi-UAV testbed for aerial manipulation applications

This paper addresses the development and implementation of a testbed for objects manipulation by using unmanned aerial vehicles AR.Drone and the VICON Cameras System. Such testbed allows the user to choose among two development environments to perform aerial manipulation establishing a communication with LabVIEW, ROS and the C++ Qt library; thus, the user can employ the development environment more suitable for his application. This testbed allows us to establish communication between a computer and the A.R. Drone (v1 or v2) via a WiFi connection which sends and receives data using the communication protocol UDP and sockets for connection with the vehicle UDP ports. This platform sends control and navigation commands to the UAVs in order to position them in the space with user interaction by means of a graphical user interface. This testbed enables the implementation of more complex applications, such as complex controllers. In addition, to validate the effectiveness of this testbed, experimental results of aerial manipulation between two quadrotors are presented.

Research on Swing up Control Based on Energy for the Pendubot System

In this paper, we present a class of nonlinear control scheme for swinging up and stabilization of an underactuated two-link robot called as Pendubot. The main objective of this paper is to present a switched control that swing up and stabilize for almost all combination of initial states given on the four equilibrium points of the double underactuated pendulum. The proposed methodology is based on two control strategies to swing up and stabilize the Pendubot system. The first one is based on Lagrangian dynamics, energy analysis, and stability theory, while the second one is based on linear quadratic regulator. Moreover, here we present a stability analysis of the switched control algorithm. In order to verify the proposed control strategy, experimental results were performed.

Semi-global leader-follower consensus for networked unmanned multi-aircraft systems with input saturation

This paper deals with the design of a consensus algorithm for a multi-aircraft (type Quadrotor) leader-follower system. This algorithm uses directed communication topologies, as well as input saturation for the follower agents. The convergence analysis of the proposed strategies is analyzed by using Lyapunov stability theory. Semi-global asymptotic consensus tracking is obtained for the case of leader with input zero, while semi-global practical consensus tracking is achieved for the case of leader with input non-zero. To demonstrate the effectiveness of the proposed solution, a set of simulation results is presented.

Global stability of PD+ controller with velocity estimation

This paper addresses the demonstration of global asymptotic convergence for the PD+ compensator. The proposed strategy is developed for a Robotic Manipulator process, which is a typical Electro-Mechanical System (when only the joint positions are available to be measured). It is well known that in the case of robot manipulators, the optical incremental encoders are widely used to monitor joints positions information, however, joints velocities can only be measured by processing the position data (by filtering or by state estimation). The proposed feedback strategy is based on nonlinear state estimation with a Luenberger-like observer. The main result is based on the knowledge of the system dynamics for the design of a nonlinear observer in order to conclude with Global Asymptotic Convergence of the system trajectories by using a particular Lyapunov function.

Robust Trajectory Tracking for Unmanned Aircraft Systems using a Nonsingular Terminal Modified Super-Twisting Sliding Mode Controller

Precision trajectory tracking problem for Unmanned Aerial Systems (UAS) is addressed in this work. A novel algorithm that combines a Nonsingular Modified Super-Twisting Controller with a High Order Sliding Mode Observer to enable an aerial vehicle tracking a desired trajectory under the assumption that i) its translational velocities are not available and ii) there are unmodeled dynamics and external disturbances. The proposed Sliding Mode Controller is based on a nonlinear sliding mode surface that ensures that the position and velocity tracking errors of all system’s state variables converge to zero in finite time. Moreover, the proposed controller generates a continuous control signal eliminating the chattering phenomenon. Finally, simulation results and an extensive set of experiments are presented in order to illustrate the robustness and effectiveness of the proposed control strategy.