Anand Sanchez

Stabilization and Trajectory Tracking of a Quad-Rotor Using Vision

We propose a vision-based position control method, with the purpose of providing some level of autonomy to a quad-rotor unmanned aerial vehicle. Our approach estimates the helicopter X-Y-Z position with respect to a landing pad on the ground. This technique allows us to measure the position variables that are difficult to compute when using conventional navigation systems, for example inertial sensors or Global Positioning Systems in urban environment or indoor. We also present a method to measure translational speed in a local frame. The control strategy implemented is based on a full state feedback controller. Experimental results validate the effectiveness of our method.

Real-time embedded control system for VTOL aircrafts: Application to stabilize a quad-rotor helicopter

In this paper, we present the design of an autopilot embedded control system for VTOL aircrafts using low cost sensors. The embedded control system uses parallel processing architecture. In addition, multitasking software is used to implement the data acquisition, control law computation, and correction output to get the desired set point. The control law can be easily tuning to improve the performance of the vehicle. We evaluate the performance of this platform in a quad-rotor helicopter. The main goal is to achieve the stationary flight using two control strategies, a linear PD control and nonlinear nested saturations control. Real time experiments show that the autopilot is a platform relievable with low cost components.

Hovering Flight Improvement of a Quad-rotor Mini UAV Using Brushless DC Motors

This paper present the design of a novel embedded control system for improving attitude stabilization of a quad-rotor mini UAV. The control strategy uses low cost components and includes an extra control loop based on motor armature current feedback. This additional control loop significantly improves the performance of the quad-rotor attitude stability. This technique results in a controller that is robust with respect to external disturbances as has been observed experimentally.

Modeling and Global Control of the Longitudinal Dynamics of a Coaxial Convertible Mini-UAV in Hover Mode

The aim of this paper is to present a configuration for a Convertible Unmanned Aerial Vehicle, which incorporates the advantages of the coaxial rotorcraft for hover flight and the efficiencies of a fixed-wing for forward flight. A detailed dynamical model, including the aerodynamics, is obtained via the Newton-Euler formulation. It is proposed a nonlinear control law that achieves global stability for the longitudinal vertical-mode motion. Indeed, we have performed a simulation study to test the proposed controller in presence of external perturbations, obtaining satisfactory results. We have developed an embedded autopilot to validate the proposed prototype and the control law in hover-mode flight.

Discrete-time stabilization of integrators in cascade: Real-time stabilization of a mini-rotorcraft

This paper deals with the problem of stabilizing n integrators in cascade with bounded input using a discrete-time controller. We propose here a control algorithm using saturation functions for the case of 3 integrators and then we extend the development to the case of n integrators. The control methodology developed is simple and is explicitly given. We present a real-time application of the proposed control algorithm for the stabilization of the orientation of a mini-rotorcraft

A new UAV configuration having eight rotors: Dynamical model and real-time control

In this paper we present an original configuration of a small aerial vehicle having eight rotors, four of them are devoted to stabilize the helicopter and the rest are used to drive the lateral displacements. The dynamical model is obtained using Euler-Lagrange approach, the attitude dynamics (roll, pitch and yaw) are practically independent of the translational dynamics corresponding to the lateral displacements (x and y), except for a small compensation on the angles roll and pitch. This compensation is directly related to the velocity of corresponding lateral motors of each axis. With this particular configuration many task could be simplified, reducing the complexity to develop an autonomous flight. Moreover, we are able to apply an easier control strategy for the flying machine.

Continuous reactive-based position-attitude control of quadrotors

A new control scheme for position-orientation tracking of underactuated quadrotor robotic vehicle is proposed. A quaternion-based sliding surface parametrizes the open-loop error equation of orientation dynamics, then a second order sliding mode (SOSM) is synthesized for global exponential stabilization of attitude coordinates along an orientation equilibrium manifold. This SOSM for any initial condition leads to a simplified design of a torque PD controller for position dynamics, for globally uniformly ultimately bounded of position trajectories. The SOSM reacts to the effect of the PD as if it were an endogenous persistent disturbance, which vanishes until it reaches its equilibrium position manifold. In contrast to other results that consider the full model without linearization nor further simplifications, our proposal yields a controller which is smooth and does not require the dynamic model. Since the parametrization of attitude representation is global, aggressive maneuvering capabilities are exhibited. Simulations are presented for a variety of flight regimes, including carry out helixes and loops at high angular velocities. Real-time experiments provide a glimpse of the closed-loop performance for a custom made quadrotor.

Parametric Robust Stability Analysis for Attitude Control of a Four-rotor mini-rotorcraft

This paper presents new results to compute the robustness margin of an attitude control system of a four-rotor mini-rotorcraft. The maximum parametric uncertainty is computed when a multivariable PD control is used to stabilize the attitude of the aerial vehicle. This work is based on the value set characterization of the mathematical model for the control system. This mathematical model is represented by an interval plant with time delay. The zero exclusion principle is used to compute the robustness margin of the closed loop control system. This approach transforms the original robust stability problem into simple graphic inspection problem where we only need to verify if a graph on the complex plane contains the origin or not. Furthermore, real-time experiments are presented which show the satisfactory performance of the proposed control strategy

Free-model fractional-order absolutely continuous sliding mode control for euler-lagrange systems

Euler-Lagrange systems, such as robots, exhibit benign structural properties, including passivity, which allow us to design robust and efficient energy-shaping controllers. A great variety of passivity-based control schemes are available and recently model-based fractional order discontinuous sliding mode control has been proposed. In this paper, a fractional order absolutely continuous control scheme for Euler-Lagrange systems is proposed, without depending on the dynamic model, which enforces in finite-time a commensurable rational fractional order regime. Additionally, a frequency domain analysis is addressed, which is very useful for some applications. A numerical simulation assessment is presented, including the frequency domain response based on Bode plots. Final concluding remarks are discussed in view of the state of the art in fractional order controllers.

Toward force control of a quadrotor UAV in SE(3)

Two novel model-free second order sliding mode controllers are proposed for the constrained underactuated position and orientation dynamic model of the quadrotor, i.e., considering contact wrench, based on spring-like contact force model. The main theorem establishes conditions for the closed-loop system to guarantee semi-global exponential and robust tracking of position and admissible contact forces, with zero yaw, by exploiting the solution in SE(3). It is proved an integral sliding mode for all time and for any initial condition at a quaternion-based sliding surface. This yields a causal and analytical computation of desired angular velocity in terms of position control, without involving derivatives of the state. A second theorem is derived for terminal stability with desired finite time convergence. This in turns produces three results, a) a singularity-free representation under proper and easy to meet initialization; b) stable transition from free flying to constrained motion, and c) realization of the virtual position controller due to finite time convergence of angular tracking errors. It is noted that there arises an evident physical limit for force interaction along underactuated directions: the more interaction force along the underactuated axes, the more roll and pitch angles are needed the less thrust that can be produced to sustain the UAV in the air. Comprehensive simulation study is discussed under various flying conditions, and finally, the explicit (active) force control, based on a differential algebraic model, is briefly addressed.