Embedded system for controlling a mini underwater vehicle in autonomous hover mode E. Campos * I. Torres * O. Garcia. * J. Torres * R. Lozano *,** * Laboratoire Franco-Mexicain d’Informatique et Automatique, LAFMIA UMI 3175 CNRS-CINVESTAV Mexico e-mails:{ecampos,itorres,ogarcias,jtorres,rlozano}@ctrl.cinvestav.mx. ** Laboratoire Heudiasyc, Universit´ e de Technologie de Compi` egne, Compi` egne, France e-mail:rlozano@hds.utc.fr Abstract: This work presents the development of a mini underwater vehicle (Triton-PR), the embedded system, and the experiments in real-time for autonomous hover operation. Artificial vision allows the vehicle to obtain the translational position and velocity. The main characteristic of the embedded system is the implementation of low cost devices and materials, besides the number and location of the thrusters was chosen in order to have enough power and generate the rotation and translation movements. The dynamical model of the (Triton-PR) is described by the classic Euler-Lagrange equations, and a PD controller based on saturation functions is proposed for providing autonomous attitude and position of the robot. Finally, the performance of the vehicle is shown in simulation and real-time experimental results. Keywords: Underwater vehicle, Embedded system, Artificial vision, Saturation functions, Real-time experiments. 1. INTRODUCTION In recent years, there has been a growing interest in the development of Autonomous Underwater Vehicles (AUVs). Surveillance in pipelines, building subsea infrastructure, and microscopic life monitoring are civilian missions, while anti- submarine warfare, battle group surveillance are objectives for military missions. Some mini submarine vehicles are capable of navigating in cluttered and deep ocean environments. AUVs require mecha- nisms such as diving planes, rudders, and tilt-thrusters in order to accomplish the desired objectives. Advances in electronic system, video processing and data acquisition have made of ma- chine vision systems a very powerful tools and more affordable, see Fan et al. (2001), Kleeman (2003), Stewart et al. (2001). Many contributions about mini submarine vehicles have been reported in the literature. An automatic visual station keeping of an eight ducted thrusters underwater robot is discussed in Marks et al. (1994). The robot position is obtained by tracking texture features based on the image filtering and correlation. In Jin et al. (1996), a PID control strategy for an AUV based on a vision system which estimates the vehicle position is presented. In van der Zwaan et al. (2001), the design and implementation of a control system are presented for an automatic vision-based station keeping with an underwater ROV relative to some visual landmark. The main contribution of this paper is to present the marine robot (Triton-PR submarine), embedded system and real-time experiments using artificial vision. The dynamic model is de- scribed using the classic Euler-Lagrange formulation following the ideas proposed by Fossen (1999), while the stable operation is ensured by a nonlinear controller based on saturation func- tions to achieve the global stability of the vehicle in orientation and position. In addition, an onboard camera has been installed for obtaining the position with respect to a landmark while the velocity of the vehicle is estimated by using an optical flow algorithm. However, our prototype was developed with low- cost devices and materials, for instance the vision device is a standard webcam. The paper is organized as follows. Section 2 introduces an oper- ational description, the embedded system and the visual sensor of the vehicle. The dynamic model obtained from the classic Euler-Lagrange equations, and the control strategy based on saturation functions are presented in Section 3. In Section 4 describes the simulation results of the closed-loop system. The real-time experiments are shown in section 5. Finally, section 6 presents the conclusions and future works. 2. UNDERWATER ROBOT Operational description The Triton-PR submarine is a mini underwater vehicle whose propulsion system consists of five thrusters (DC motors) driving marine propellers. The size of this marine vehicle is about 35 cm long and 20 cm diameter, and its structure is built of Ny- lamid. Due to its cylindric structure, the Triton-PR submarine is capable of operating in either hover or cruise mode. This vehicle does not have control surfaces (diving plane or rudder) for performing hover mode. Concerning the rotational motion of this vehicle, yaw control is performed through differential speed control of the thrusters 4 and 5. Pitch control is obtained similarly using thrusters 1, 2 and 3 whereas the roll control used thrusters 2 and 3. On the other hand, the translational motion of the z axis is regulated by decreasing or increasing the com- Proceedings of the 1st IFAC Conference on Embedded Systems, Computational Intelligence and Telematics in Control - CESCIT 2012 3-5 April 2012. Würzburg, Germany 978-3-902661-97-5/12/$20.00 © 2012 IFAC 266 10.3182/20120403-3-DE-3010.00041