Greetings from NASA Houston,

While at NASA, Yong-Lae and I asked Toby Martin about the Quantum Tunneling
Current (QTC) skin that they have used on Robonaut. They have been using sheets
from the same British company that supplies materials to Shadow Robotics. In
appearance, stiffness and texture, it is rather like the PDMS sheets that Aaron
Parness has been spinning for his microwedges. The tunneling effect gives an
approximately logarithmic conduction rate with pressure.

They use it on a flexible printed circuit with closely-spaced adjacent
electrodes for +voltage and ground. On pressure, the current takes a U shaped
path between adjacent pads on the printed circuit.  They do not try to bond the
pads to the skin (e.g. with conductive epoxy). Nor have they tried to pattern a
circuit directly onto the skin (e.g. by sputtering of vapor deposition).

They found a supplier who will make them small quantities of very precise, very
flexible double-sided printed circuits which they wrap around the Robonaut
fingers. Toby could not remember the supplier. Maybe Minco? Cirexx?  But the
circuits are certainly higher resolution and quality that Will Provancher was
able to fabricate in my lab.

Toby says  the circuit/skin combination gives a substantially better (more
repeatable, less hystersis) sensor than the FSRs that they used previously. They
cover the QTC skin with an outer skin of what looks like neoprene or urethane
for durability. To obtain better sensitivity at light pressures, they place
glass beads directly over where the contact pads are to increase the local
pressure.

cheers,

Mark C.