title: Time-of-Travel Methods for Measuring Optical Flow on Board a Micro Flying Robot.
abstract: For use in autonomous micro air vehicles, visual sensors must not only be small, lightweight and insensitive to light variations; on-board autopilots also require fast and accurate optical flow measurements over a wide range of speeds. Using an auto-adaptive bio-inspired Michaelis-Menten Auto-adaptive Pixel (M 2 APix) analog silicon retina, in this article, we present comparative tests of two optical flow calculation algorithms operating under lighting conditions from 6 × 10 - 7 to 1 . 6 × 10 - 2 W·cm - 2 (i.e., from 0.2 to 12,000 lux for human vision). Contrast "time of travel" between two adjacent light-sensitive pixels was determined by thresholding and by cross-correlating the two pixels' signals, with measurement frequency up to 5 kHz for the 10 local motion sensors of the M 2 APix sensor. While both algorithms adequately measured optical flow between 25 ∘ /s and 1000 ∘ /s, thresholding gave rise to a lower precision, especially due to a larger number of outliers at higher speeds. Compared to thresholding, cross-correlation also allowed for a higher rate of optical flow output (99 Hz and 1195 Hz, respectively) but required substantially more computational resources.
authors.affiliation: Aix-Marseille Université, CNRS, ISM UMR7287, 13288 Marseille Cedex 09, France. erik.vanhoutte@univ-amu.fr.
authors.forename: Erik
authors.initials: E
authors.lastname: Vanhoutte
authors.affiliation: Aix-Marseille Université, CNRS, ISM UMR7287, 13288 Marseille Cedex 09, France. stefano.mafrica@mpsa.com.
authors.forename: Stefano
authors.initials: S
authors.lastname: Mafrica
authors.affiliation: Aix-Marseille Université, CNRS, ISM UMR7287, 13288 Marseille Cedex 09, France. franck.ruffier@univ-amu.fr.
authors.forename: Franck
authors.initials: F
authors.lastname: Ruffier
authors.affiliation: Aix-Marseille Université, CNRS, ISM UMR7287, 13288 Marseille Cedex 09, France. reinoud.bootsma@univ-amu.fr.
authors.forename: Reinoud J
authors.initials: RJ
authors.lastname: Bootsma
authors.affiliation: Aix-Marseille Université, CNRS, ISM UMR7287, 13288 Marseille Cedex 09, France. julien.serres@univ-amu.fr.
authors.forename: Julien
authors.initials: J
authors.lastname: Serres
keywords: VLSI retina; bio-inspired robotics; bionics; biorobotics; micro air vehicle (MAV); optic flow sensor; sense and avoid