When it comes to building realistic robots, it’s not just
the way they look that’s important. It’s also the way they feel to the touch,
says John-John Cabibihan at the National University of Singapore and pals. They
argue that if robots are ever to be accepted socially, they will need to have
humanlike skin so that actions such as handshakes can be made as realistic as
possible.
Of course, it’s not just a robot’s sense of social standing at stake. There’s
also the issue of human prosthetics. While these are becoming increasingly
realistic to the eye, they are still far from convincing to the touch.
How close are we to synthetic skin that can change all this? A fair way off, if
the results of Cabibihan and co’s investigations are anything to go by. They
compared the properties of two commonly used synthetic skins, silicone and
polyurethane, with the human variety and found them sadly wanting.
Human skin, it seems, has some special properties that are difficult to
replicate. Cabibihan and co measured three properties: skin compliance, or the
degree to which it is deformed by a force; conformance, or the way its shape
conforms to an object it touches; and hysteresis, or the energy dissipated
under a load–essentially the difference between the way it deforms and reforms.
Synthetic materials require more force to bend them, but they dissipate less
energy during this process. So they are unable to match the hysteresis curve of
human skin, which looks particularly challenging to reproduce. That’s probably
because the hysteresis properties are the result of the interaction between the
various layers that make up human skin.
The big question for the designers of robotic and prosthetic skin is whether
these characteristics can be reproduced by a single layer or whether a more
complex (and expensive) skin made of multiple layers will be needed.
On the current evidence, the single-layered approach looks limited.
Ref: arxiv.org/abs/0909.3559 :Towards Humanlike Social Touch for Sociable Robotics and Prosthetics: Comparisons on the Compliance, Conformance and Hysteresis of Synthetic and Human Fingertip Skins