Flexible sensors make robot skin
By Eric Smalley,
Technology Research News
Skin is very useful. In addition to neatly separating self from other, it
provides all kinds of feedback.
Researchers from the University of Tokyo have devised pressure-sensor
arrays that promise to give objects like rugs and robots the equivalent of one
aspect of skin -- pressure sensitivity.
The researchers' pressure sensor arrays are built from inexpensive
organic, or plastic, transistors on a flexible material. This allows for dense
arrays that can be used over large areas.
The arrays could be used in pressure-sensitive coverings in hospitals,
homes, gyms and cars to monitor people's health and performance, and eventually
as skin that would give robots the means to interact more sensitively with their
surroundings, said Takao Someya, an associate professor of electrical
engineering at the University of Tokyo.
The sensor skin works even when rolled around a cylinder as small as 4
millimeters in diameter, said Someya. The researchers' prototype is an eight-centimeter-square
sheet containing a 32-by-32 array of organic sensors -- a density of 16 sensors
per square centimeter. In contrast, humans have 1,500 pressure sensors per
square centimeter in the fingertips, though far fewer in most other places.
The pressure sensor arrays could be used in pressure carpets that
distinguish family members from strangers or sense when a hospital patient
collapses.
The active-matrix design allows the arrays to be smart enough to enable
specific sensors at certain feedback points to, for instance, monitor the heart
and breathing rate of a hospital patient who has fallen to the floor, said
Someya. The skin could measure whether an elderly patient is just taking a rest,
or needs help, he said.
Because organic transistor-based electronics are potentially very cheap,
"it is not unrealistic to spread pressure carpets all over the floor in your
house," said Someya.
The skin could also be used in car seats to monitor drivers' mental and
physical conditions, Someya said. "Our large-area pressure [sensing abilities]
would be helpful" in obtaining information through drivers seats, he said.
The skin could eventually be used to make domestic robots more
appropriately sensitive of their surroundings, said Someya. "Robots working at
home definitely require touch sensitivity," said Someya. This has proven
difficult, he said. "It is not trivial matter to give a robot the ability to
pick up an egg."
A pressure-sensitive skin would be helpful in making robots that are
capable of gently lifting a person or avoiding injuring people, said Someya.
The prototype's pressure-sensitive rubber layer contains electrically
conductive graphite particles that change the layer's electrical resistance when
pressure is applied. This half-millimeter-thick layer and a copper electrode are
laminated to an array of organic transistors. Because the pressure-sensitive
layer and the electrode are unpatterned, only the transistor assembly requires
alignment, making the manufacturing process relatively simple, according to
Someya.
The sensors are controlled by an active matrix that uses a transistor to
record signals from each sensor in the array. The active matrix means that only
one transistor is on for each stimulated sensor, which allows for lower power
consumption and greater control than simpler pressure sensor arrays that wire
sensors together in grids. This makes the pressure-sensitive skin appropriate
for large-area sensor arrays, according to Someya.
Organic transistors are considerably larger and slower than the silicon
transistors used in most electronics, but they are also very cheap -- they can
be manufactured using a printing process. Many groups of researchers are working
to make speedier versions of organic transistors. The pressure-sensitive skin,
however, is an appropriate application for today's relatively large and slow
versions, said Someya.
There is work to be done before the pressure-sensitive skin is ready for
practical use, said Someya. The main challenge is making the organic transistors
more reliable, he said. The electrical characteristics of organic transistors
change in a matter of days, said Someya. To be practical, however, organic
transistors should be stable for years, he said.
Electronic skin could be ready for practical use in four to five years,
said Someya.