  In this paper we present an early prototype of the Digger Finger that is
designed to easily penetrate granular media and is equipped with the GelSight
sensor. Identifying objects buried in granular media using tactile sensors is a
challenging task. First, particle jamming in granular media prevents downward
movement. Second, the granular media particles tend to get stuck between the
sensing surface and the object of interest, distorting the actual shape of the
object. To tackle these challenges we present a Digger Finger prototype. It is
capable of fluidizing granular media during penetration using mechanical
vibrations. It is equipped with high resolution vision based tactile sensing to
identify objects buried inside granular media. We describe the experimental
procedures we use to evaluate these fluidizing and buried shape recognition
capabilities. A robot with such fingers can perform explosive ordnance disposal
and Improvised Explosive Device (IED) detection tasks at a much a finer
resolution compared to techniques like Ground Penetration Radars (GPRs).
Sensors like the Digger Finger will allow robotic manipulation research to move
beyond only manipulating rigid objects.
