Visual servo system based on a biologically-inspired scanning sensor

In the framework of our biologically inspired robotics approach, we describe a visually-guided demonstration model aircraft, the attitude of which is stabilized in yaw by means of a novel, non emissive optical sensor having a small visual field. This aircraft incorporates a miniature scanning sensor consisting of two photoreceptors with adjacent visual axes, driving a Local Motion Detector (LMD), which are made to perform a low-amplitude scanning at a varying angular speed. Under these conditions, the signal output from the motion detector varies gradually with the angular position of a contrasting object placed in its visual field, actually making the complete system a non-emissive optical "position sensor". Its output, remarkably, (i) varies quasi-linearly with the angular position of the contrasting object, and (ii) remains largely invariant with respect to the distance to the object and its degree of contrast. We built a miniature, twin-engine, twin-propeller aircraft (weight 100 grammes) equipped with this visual position sensor. After incorporating the sensor into a visuomotor feedback loop enhanced by an inertial sensor, we established that the "sighted aircraft" can fixate and track a dark edge placed in its visual field, thus opening the way for the development of visually-guided systems for controlling the attitude of micro-air vehicles, of the kind observed in insects such as hover-flies.