Stephane Viollet

A Vision-based Steering Control System for Aerial Vehicles

Ever since animals endowed with visual systems made their first appearance during the Cambrian era, selection pressure led many of these creatures to stabilize their gaze. Navigating in 3-D environments (Collett & Land 1975), hovering (Kern & Varju 1998), tracking mates (N. Boeddeker, Kern & Egelhaaf 2003) and intercepting prey (Olberg et coll. 2007) are some of the many behavioural feats achieved by flying insects under visual guidance. Recent studies on free-flying flies have shown that these animals are able to keep their gaze fixed in space for at least 200ms at a time, thanks to the extremely fast oculomotor reflexes they have acquired (Schilstra & Hateren 1998). In vertebrates too, eye movements are also the fastest and most accurate of all the movements. Gaze stabilization is a difficult task to perform for all animals because the eye actuators must be both : • fast, to compensate for any sudden, untoward disturbances. • and accurate, because stable visual fixation is required. In the free-flying fly, an active gaze stabilization mechanism prevents the incoming visual information from being affected by disturbances such as vibrations or body jerks (Hengstenberg 1988) (Sandeman 1980)(Schilstra & Hateren 1998). This fine mechanism is way beyond what can be achieved in the field of present-day robotics. The authors of several studies have addressed the problem of incorporating an active gaze stabilization system into mobile robots. A gaze control system in which retinal position measurements are combined with inertial measurements has been developed (Yamaguchi & Yamasaki 1994), and its performances were assessed qualitatively while slow perturbations were being applied by hand. Shibata and Schaal (Shibata et coll. 2001) designed a gaze control system based on an inverse model of the mammalian oculomotor plant. This system equipped with a learning network was able to decrease the retinal slip 4-fold when sinusoidal perturbations were applied at moderate frequencies (of up to 0.8Hz). Another adaptive image stabilizer designed to improve the performances of robotic agents was built and its ability to cope with moderate-frequency perturbations (of up to 0.6Hz) was tested (Panerai, Metta & Sandini 2002). Three other gaze stabilization systems inspired by the