  Vision-based tactile sensors have recently become popular due to their
combination of low cost, very high spatial resolution, and ease of integration
using widely available miniature cameras. The associated field of view and
focal length, however, are difficult to package in a human-sized finger. In
this paper we employ optical fiber bundles to achieve a form factor that, at 15
mm diameter, is smaller than an average human fingertip. The electronics and
camera are also located remotely, further reducing package size. The sensor
achieves a spatial resolution of 0.22 mm and a minimum force resolution 5 mN
for normal and shear contact forces. With these attributes, the DIGIT Pinki
sensor is suitable for applications such as robotic and teleoperated digital
palpation. We demonstrate its utility for palpation of the prostate gland and
show that it can achieve clinically relevant discrimination of prostate
stiffness for phantom and ex vivo tissue.
