Bio-inspired eye stabilizes robot’s flight, replaces inertial navigation system

March 11, 2015

The BeeRotor robot, equipped with an eye inspired by insects (credit: Expert & Ruffier (ISM, CNRS/AMU))

Biorobotics researchers have developed the first aerial robot able to fly over uneven terrain that is stabilized visually without an accelerometer.

Called BeeRotor, it adjusts its speed and avoids obstacles thanks to optic flow sensors inspired by insect vision.

It can fly along a tunnel with uneven, moving walls without measuring either speed or altitude. The study was published on February 26 in the journal Bioinspiration & Biomimetics.

Aircraft, ships, and spacecraft currently use a complex inertial navigation system based on accelerometers and gyroscopes to continuously calculate position, orientation, and velocity without the need for external references (known as dead reckoning).

Researchers Fabien Expert and Franck Ruffier at the Institut des Sciences du Mouvement – Etienne-Jules Marey (CNRS/Aix-Marseille Université) decided to create simpler system,  inspired by winged insects. They created BeeRotor, a tethered flying robot able for the first time to adjust its speed and follow terrain with no accelerometer and without measuring speed or altitude, avoiding vertical obstacles in a tunnel with moving walls.

To achieve this, the researchers mimicked the ability of insects to use the passing landscape as they fly. This is known as “optic flow,” the principle you can observe when driving along a road: the view in front is fairly stable, but looking out to either side, the landscape passes by faster and faster, reaching a maximum at an angle of 90 degrees to the path of the vehicle.

To measure optic flow, BeeRotor is equipped with 24 photodiodes (functioning as pixels) distributed at the top and the bottom of its “eye.” This enables it to detect contrasts in the environment as well as their motion. As in insects, the speed at which a feature in the scenery moves from one pixel to another provides the angular velocity of the flow. When the flow increases, this means that either the robot’s speed is increasing or that the distance relative to obstacles is decreasing.

By way of a brain, BeeRotor has three feedback loops: altitude (following the floor or roof), speed (adapting to the size of the tunnel) and stabilization of the eye in relation to the local slope. This enables the robot to always obtain the best possible field of view, independently of its degree of pitch. That allows BeeRotor to avoid very steeply sloping obstacles (see video) no accelerometer and no measures of speed or altitude.

BeeRotor suggests a biologically plausible hypothesis to explain how insects can fly without an accelerometer: using cues from optic flow to remain stable via feedback loops.

Optic flow sensors also have industrial applications: such as replacing heavy accelerometers for small robots and as an ultra-light backup system in the event of failure on a space mission.

Expert & Ruffier, ISM (AMU / CNRS) | Beerotor Video (Multimedia Extension 2)

Abstract of Flying over uneven moving terrain based on optic-flow cues without any need for reference frames or accelerometers

Two bio-inspired guidance principles involving no reference frame are presented here and were implemented in a rotorcraft, which was equipped with panoramic optic flow (OF) sensors but (as in flying insects) no accelerometer. To test these two guidance principles, we built a tethered tandem rotorcraft called BeeRotor (80 grams), which was tested flying along a high-roofed tunnel. The aerial robot adjusts its pitch and hence its speed, hugs the ground and lands safely without any need for an inertial reference frame. The rotorcraft’s altitude and forward speed are adjusted via two OF regulators piloting the lift and the pitch angle on the basis of the common-mode and differential rotor speeds, respectively. The robot equipped with two wide-field OF sensors was tested in order to assess the performances of the following two systems of guidance involving no inertial reference frame: (i) a system with a fixed eye orientation based on the curved artificial compound eye (CurvACE) sensor, and (ii) an active system of reorientation based on a quasi-panoramic eye which constantly realigns its gaze, keeping it parallel to the nearest surface followed. Safe automatic terrain following and landing were obtained with CurvACE under dim light to daylight conditions and the active eye-reorientation system over rugged, changing terrain, without any need for an inertial reference frame.