Francisco Gavilan

Control of the longitudinal flight dynamics of an UAV using adaptive backstepping

An adaptive backstepping approach is used to control the longitudinal dynamics of an Unmanned Air Vehicle (UAV). The nonlinear controller designed makes the system follow references in the aerodynamic velocity and ight path angle, using the elevator deections and the thrust as actuators. Moreover, the (global) solution is valid for all the ight envelope, since it is based on a general nonlinear model. The adaptation scheme proposed allowed us to design an explicit controller with a minimal knowledge of the aircraft aerodynamics. Simulations are included for a realistic UAV model that includes actuator saturation.

Adaptive Control for Aircraft Longitudinal Dynamics with Thrust Saturation

An output-feedback control law is designed for the longitudinal flight dynamics of an aircraft. The proposed control law is designed using the adaptive backstepping method and does not require any knowledge of aircraft aerodynamics beyond well-known qualitative physical properties. The resulting feedback controller is able to follow given references in both airspeed and flight-path angle by actuating elevator deflections and aircraft engine thrust. Engine physical limits are incorporated into the design by using a Lyapunov function analysis that includes saturation, obtaining a novel hybrid adaptation law that guarantees closed-loop system stability. Simulation results show good performance of the feedback law and, in particular, demonstrate that the hybrid adaptation law improves the behavior of the closed-loop system when saturations are present. A degraded scenario (a sudden cargo displacement that renders the aircraft statically unstable) is also considered to show the adaptation capabilities of the c...

An iterative model predictive control algorithm for UAV guidance

A novel aircraft path-following guidance algorithm based on model predictive control is proposed in this paper. The algorithm tracks a precomputed trajectory and produces reference commands for a low-level attitude controller. To solve the associated nonlinear optimization problem, an iterative scheme is proposed, using as a feasible hotstart the guidance solution provided by a well-behaved L1 navigation law. Simulations show the effectiveness of the algorithm, even in the presence of disturbances such as wind.

Trajectory Planning for Spacecraft Rendezvous with On/Off Thrusters*

Abstract The objective of this work is to present a trajectory planning algorithm for spacecraft rendezvous that is able to incorporate Pulse-Width Modulated (PWM) control signals. The algorithm is based on linearization around a previously computed solution. To initialize the algorithm, a first solution needs to be obtained. To do so, the trajectory planning problem is solved using Pulse-Amplitude Modulated (PAM) control signals; these are then converted to PWM signals, which are used as an initial guess. Iterating, the solution is refined until an optimal value is reached. Simulations show that this method converges after a few iterations. The algorithm is simple and fast, hence it could be implemented online or used together with a Model Predictive Controller.

Output-feedback control of the longitudinal flight dynamics using adaptative backstepping

An adaptive backstepping approach is used to design an output feedback control law for the longitudinal dynamics of an Unmanned Air Vehicle (UAV). The resulting nonlinear controller makes the system to follow references in the aerodynamic velocity and flight path angle, using elevator deflections and thrust as actuators. Only measurable quantities are used in the control and adaptation laws. The proposed strategy allows to design an explicit controller without any knowledge of the aerodynamic coefficients or the trim angle of attack, which also depends on the aerodynamic coefficients; only well-known qualitative physical properties from aerodynamics are used. Simulations are included for a realistic UAV model including actuator saturation.

Trajectory Planning for Spacecraft Rendezvous in Elliptical Orbits with On/Off Thrusters

Abstract In a previous work, the authors developed a trajectory planning algorithm for spacecraft rendezvous which computed optimal Pulse-Width Modulated (PWM) control signals, assuming that the target was moving in a circular Keplerian orbit. In this paper we extend the algorithm to the case of an elliptical target orbit with arbitrary eccentricity. Since the orbit is elliptical, the linear time-varying Tschauner-Hempel model is used, whose exact solution is possible by using true (or eccentric) anomaly instead of time (which is directly related to both via Keplers equation). Unlike in the circular case, computing the PWM solution itself requires numerical integration. However, explicit linearization around the computed solution turns out to be possible and is exploited for rapidly improving the solution using linear programming (LP) techniques. The algorithm is initialized by solving the impulsive problem first; the impulses are converted to PWM signals, which are used as an initial guess. Using the explicit linearization and LP, the solution is refined until a (possibly local) optimal value is reached. The efficacy of the method is shown in a simulation study where it is compared to the impulsive-only approach.

A High-level model predictive control guidance law for unmanned aerial vehicles

This tutorial paper describes a high-level guidance algorithm based on model predictive control. The algorithm follows a precomputed flight plan (which provides a reference trajectory based on straight segments) by calculating the aerodynamic velocity, flight path angle and bank angle commands for a low level attitude controller. To compute these control signals, the guidance law uses a nonlinear 3DoF aircraft model for state prediction that leads to a nonlinear optimization problem, which is solved using a iterative scheme. The algorithm uses as a hotstart a robust missile guidance law, thus guaranteeing feasibility. Simulation results show the effectiveness of the proposed guidance law.

Development of an Emergency Radio Beacon for Small Unmanned Aerial Vehicles

Emergency locator transmitters (ELTs) used to locate manned aircrafts are not well suited to find and recover small crashed unmanned aerial vehicles (UAVs). ELTs utilize an international satellite system for search and rescue (Cospas-Sarsat System), which should leverage its expensive resources to save lives as a priority. Besides, ELTs are too big and heavy to be used within small UAVs. Some of the existing solutions for this problem are based on receivers that detect signal strength, which may be a long and tedious process not suitable for user needs. Others do not have enough range or require radio license and expensive amateur radio receivers. This paper presents an emergency radio beacon specifically designed to locate small UAVs. It is triggered automatically in the event of a crash and allows finding and recovering a crashed UAV in a fast and simple way. It meets not only the required specifications of user-friendliness, size and weight of this kind of application, but also it is a high precision and low cost device. Besides, it has enough range and endurance. The experiments carried out show the operation of the proposed system.