  Soft optical tactile sensors enable robots to manipulate deformable objects
by capturing important features such as high-resolution contact geometry and
estimations of object compliance. This work presents a variable stiffness soft
tactile end-effector called StRETcH, a Soft to Resistive Elastic Tactile Hand,
that is easily manufactured and integrated with a robotic arm. An elastic
membrane is suspended between two robotic fingers, and a depth sensor capturing
the deformations of the elastic membrane enables sub-millimeter accurate
estimates of contact geometries. The parallel-jaw gripper varies the stiffness
of the membrane by uni-axially stretching it, which controllably modulates
StRETcH's effective modulus from approximately 4kPa to 9kPa. This work uses
StRETcH to reconstruct the contact geometry of rigid and deformable objects,
estimate the stiffness of four balloons filled with different substances, and
manipulate dough into a desired shape.
