  Tactile perception using vibration sensation helps robots recognize their
environment's physical properties and perform complex tasks. A sliding motion
is applied to target objects to generate tactile vibration data. However,
situations exist where such a sliding motion is infeasible due to geometrical
constraints in the environment or an object's fragility which cannot resist
friction forces. This paper explores a novel approach to achieve
vibration-based tactile perception without a sliding motion. To this end, our
key idea is injecting a mechanical vibration into a soft tactile sensor system
and measuring the propagated vibration inside it by a sensor. Soft tactile
sensors are deformed by the contact state, and the touched objects' shape or
texture should change the characteristics of the vibration propagation.
Therefore, the propagated-vibration data are expected to contain useful
information for recognizing touched environments. We developed a prototype
system for a proof-of-concept: a mechanical vibration is applied to a
biomimetic (soft and vibration-based) tactile sensor from a small, mounted
piezoelectric actuator. As a verification experiment, we performed two
classification tasks for sandpaper's grit size and a slit's gap widths using
our approach and compared their accuracies with that of using sliding motions.
Our approach resulted in 70% accuracy for the grit size classification and 99%
accuracy for the gap width classification. These results are comparable to or
better than the comparison methods with a sliding motion.
