A UAV for bridge inspection: Visual servoing control law with orientation limits Najib Metni a, ⁎ , Tarek Hamel b a Laboratoire Centrale des Ponts et Chaussées, 58 bld Lefebure, 75732 Paris, France b 13S-CNRS, 2000 route des Lucioles, 06903 Sophia Antipolis, France Accepted 22 December 2006 Abstract This paper describes the dynamics of an unmanned aerial vehicle (UAV) for monitoring of structures and maintenance of bridges. It presents a novel control law based on computer vision for quasi-stationary flights above a planar target. The first part of the UAV's mission is the navigation from an initial position to a final position in an unknown 3D environment. The new control law uses the homography matrix computed from the information obtained from the vision system. The control scheme will be derived with backstepping techniques. In order to keep the camera's field of view, the control law uses saturation functions for bounding the UAVorientation and limiting it to very small values. © 2007 Elsevier B.V. All rights reserved. Keywords: Bridge inspection; Visual servoing; Unmanned aerial vehicles; Automation 1. Introduction Rapid advances in control theories, computing abilities, communications, and sensing technology offer a great tool for the unmanned aerial vehicles technology. In the last two decades a great interest in the UAV technology has risen in military applications, and many projects have been studied and applied. In LCPC-Paris (Laboratoire Central des Ponts et Chaussées), we have started a project pertaining to civil applications of a UAV: bridge inspection and traffic surveillance. This project for bridges’ inspection is called PMI (Plate-forme Mobile d'Instru- mentation) which is a UAV capable of quasi-stationary flights whose mission is the inspection of bridges and location of defects and cracks. Ageing infrastructure has become a major concern in western European countries. In France, roughly half of the bridge life cost is due to repairing and maintenance. Since many bridges were built in the sixties, health diagnostics and assessment of residual life already proves very important and will become increasingly crucial in the following decades. To this end, systematic bridge inspection has been organized for a long time and well-defined visual observation and reporting task are periodically carried out on bridges [1,2], this inspection must be done at least once every 6 years to control the evolution of defects and cracks. Current visual inspection involves a rather heavy logistics. A large platform mounted on a heavy truck is Automation in Construction 17 (2007) 3 – 10 www.elsevier.com/locate/autcon ⁎ Corresponding author. Tel.: +33 1 40436510; fax: +33 1 40436513. E-mail address: metni@lcpc.fr (N. Metni). Fig. 1. Footbridge for crack's inspection. 0926-5805/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.autcon.2006.12.010