Robots get sensitive: electronic skin could give machines a sophisticated sense of touch.
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Robots get sensitive
Electronic skin could give machines a sophisticated sense of
A flexible friend: rubber
polymers form the basis of
an electronic skin.
developed the skin. A sense of touch would help them to
identify objects, carry out delicate tasks and avoid collisions.
But while a lot of effort has gone into vision and voice
recognition for robots, touch sensitivity is still fairly
Our own skin contains a battery of touch receptors that
produce nerve signals when pressed. For gentle pressures,
the main sensors are tiny bulbs of layered tissue called
Their behaviour is mimicked in plastics such as polyvinylidene
fluoride, which generate an electric field when squeezed and
are used to make pressure-sensitive pads for computer
keyboards and other touch-triggered devices.
But for an electronic skin to have a genuine sense of touch, it
needs to be able not just to sense pressure, but to know
where it is being applied. So the skin must be covered with a
whole bank of individual sensors, each of which sends a
Someya and colleagues have wired up such a skin
consists of a sheet of rubbery polymer, impregnated with
flakes of electrically conducting graphite. The electrical
resistance of the sheet changes when it is squeezed, and this
change is detected by an array of transistors beneath the
The key challenge is to make the whole device sufficiently
flexible to behave like a true skin, so that it can be wrapped
around a robotic limb. Conventional transistors in microchips
are hard, brittle devices made from silicon. But Someya and
colleagues have made them from an flexible organic material
called pentacene. Their sensor array consists of a 32 x 32
grid of transistors, each of which is 2.5 mm square. The
researchers are hopeful that they will be able to make
transistors 100 times smaller than that if necessary.
The resulting skin can be bent quite sharply without
damaging the transistors, and continues to function even
when wrapped around a bar just 2 mm wide.
Of course our own sense of touch doesn't rely on pressure
alone; we can also detect temperature and humidity, for
example. The Japanese team hopes to add such features to
their artificial skin. They also want to make it stretchy. At
present it is more like a sheet of paper; bendy but not elastic.
"The absence of good devices of this sort has made it very
difficult to move forward", comments Robert Howe, who
works on tactile sensing for robotics at Harvard University in
Cambridge, Massachusetts. But he reserves judgement about
the impact of the new electronic skin. "Many such devices
have been proposed, but none seems to make it beyond the
Meanwhile, Someya is confident that his skin could find many
applications beyond robotics, for example in sport, security or
medicine. A pressure-sensitive carpet on the floor of a house
could distinguish family members from strangers just from
their footprints, he suggests, or sense if an elderly person
had collapsed on it. Tactile mats could monitor the
performance of athletes in the gym, while tactile seat
coverings might measure the physical condition of car drivers.
Someya, T. et al.
. Proceedings of the National Academy of
Sciences of the USA
. Advance Online Publication
Nature News Service / Macmillan Magazines Ltd 2004
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