Making Realistic Skin for Robots

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