Two optic flow regulators for speed control and obstacle avoidance

Abstract

In our project on the autonomous guidance of micro-air vehicles (MAVs) in confined indoor and outdoor environments, we have developed a bio-inspired optic flow based autopilot with which the speed of a miniature hovercraft is controlled and the walls of a straight or tapered corridor are safely avoided. A hovercraft is an air vehicle endowed with natural roll and pitch stabilization characteristics, in which planar flight control can be developed conveniently. Our own hovercraft is fully actuated by two rear and two lateral thrusters. It travels at a constant ground height (~2 mm) and senses the environment by means of two lateral eyes that measure the right and left optic flows (OFs). The complete visuo-motor control system, which is called LORA(2) (lateral optic flow regulation autopilot), consists of a system of two lateral OF regulators with a single OF set-point; (i) the first lateral OF regulator adjusts the hovercraft's forward thrust, so as to maintain the mean value of the two (right and left) OFs measured equal to a set-point. (ii) the second lateral OF regulator controls the hovercraft's side-slip thrust, so as to maintain the OF measured equal to the same set-point as in (i). Interestingly, this makes the distance to the left (D <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</sub> ) or right (D <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</sub> ) wall proportional to the forward airspeed V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> determined in (i): the faster the hovercraft is travelling, the further away from the walls it will be. Simulations have shown that the hovercraft manages to navigate in a straight or tapered corridor at speeds of up to 1 m/s although it has only a minimalistic visual system. The passive visual sensors and the simple control system used here are suitable for use on MAVs with an avionic payload of only a few grams. A major outcome of this work is that the LORA(2) autopilot makes the hovercraft navigate without any need for range sensors or speed sensors