PUB - Publikationen an der Universität Bielefeld

Tactile exploration of the near-range environment appears ubiquitous in insects. For instance, walking stick insects continuously move their pair of antennae to find footholds for their front legs. Each antenna bears different types of mechanoreceptors, each potentially contributing to touch localization. Among them, Johnston's organ, a chordotonal organ in the pedicel, probably encode contact-induced vibrations. Extracting tactile information from vibrations is a tempting approach for insectoid robots as it requires less wiring than pressure sensor arrays and, in contrast to static force sensing strategies, does not necessitate lasting contact phases. Theory shows that the first vibration modes, i.e. the lowest natural frequencies, are sufficient to estimate the radial distance of hits along a flexible beam. However, in practice, measuring low-frequency components requires proportionally long signal episodes. Not only the resulting latency would impede timely applications, like locomotion control, but also the damped vibrations may vanish too quickly. Hence, it could be beneficial to exploit higher frequency bands. Since beam theory predicts accurately only the few first vibration modes, we experimentally tested whether and which high-frequency bands could be used to estimate the contact distance along a plastic tube rotated by a servomotor. For a range of contact distances, vibrations were sampled with high rate and sensitivity, using a piezoelectric pickup for acoustic guitar, taped to the base of the antenna. Systematically varied bands of the corresponding power spectra were evaluated by support vector regression. We demonstrate that accurate distance estimates can be obtained from various frequency bands, including high-frequency ones