How a 'soft' robot hand with a sense of touch could revolutionise prosthetics

Newly revealed technology uses electric fields to detect touch

In a laboratory in Cambridge in the UK, a "soft" hand attached to a moving metal arm might just represent the future of robotics.

While robots are sometimes thought of as rigid devices with jerky movements, the growing field of soft robotics - which embraces the use of more flexible materials such as silicone rubber or in this case a hydrogel - offers a different perspective.

The hand in the Cambridge lab feels like a firm jelly – perhaps not unlike a slightly fleshy human hand – and, what is more, it has a remarkable ability to sense touch.

But, unlike some other soft robots that are also sensitive to touch, it does not have countless electrode sensors embedded in the surface of the hand. Such soft robots can be expensive to produce and easily damaged, with electrodes at risk of being ripped out.

Instead, the researcher who helped to develop the hand, Dr David Hardman, a junior research fellow in the University of Cambridge’s department of engineering, has embedded the sensors, of which there are 32, in the wrist.

Not only can the hand sense it has been touched, it can detect where and can differentiate between different stimuli.

“Was it a human touch, a piece of metal or a heat gun?” said Dr Hardman, who works in the university’s bio-inspired robotics lab. “We have a lot of redundancy and can extract what we want from the information.”

Grasping the future

Writing in Science Robotics, the researchers suggested their technology could be incorporated into new designs of soft robots.

The most obvious potential real-world application, Dr Hardman said, is in prosthetics, as such an artificial hand could sense in a similar way to a real one.

“If you can interface with the human brain, that’s very useful,” he said. “That’s the direction in which we want to go.”

Another possible application is in high-tech mattresses that sense where the user is lying, although Dr Hardman warned this was “still very much in the exploratory stage”.

Soft robotics is a field that, tying in with the name of the laboratory in which Dr Hardman works, is “much more biologically inspired”.

Much of the inspiration for this area of research came from scientists looking at the octopus and marvelling at the vast range of things these creatures can do, Dr Hardman said.

“It’s taking inspiration from nature, which has had million of years to get good at doing particular tasks,” he said.

Another robotics researcher, Prof Liang He, an associate professor of biomedical engineering at the University of Oxford, is interested in “bringing humanlike sensations to robotic agents”.

“We want our robots to be as sensitive as humans,” he said. “We also want to design a human-like skin that can better interact with humans.”

But it remains the case, scientists say, that human hands can achieve a much higher level of dexterity than even the most advanced robots.

Prof Liang indicated that while artificial hands are becoming better able to achieve particular tasks, such as detecting temperature changes or physical stress, they are a long way from matching human hand in terms of overall capability.

“In five or 10 years, in the near future, it will be difficult or nearly impossible that [a robot hand] could have the general capability of a human hand,” he said. “But we may have robot hands that in certain aspects outperform a human hand.”

How does the technology work?

The method the hand uses to sense touch is known as electrical impedance tomography and makes use of the way in which external cues, such as touch, change the electric field around the hand that is generated by electrodes.

Dr David Hardman, of the University of Cambridge, shows off the hydrogel hand he has created. Daniel Bardsley / The National

Pressing on the hand changes the way electricity is conducted across its surface, enabling the precise location of the stimulus to be worked out.

“We can use each of these [electrical] channels as a piece of the puzzle about what’s happening over the entire surface,” Dr Hardman said.

“A lot of companies making humanoids put a lot of effort into sensations but at the fingertips … there are so many tasks we can do as humans because the rest of our hands are sensitised.”

The hand itself is made from a hydrogel, a material that, containing gelatin, has some similarities with edible jelly.

In a newly published paper, Dr Hardman and his co-authors, Prof Fumiya Iida, a professor of robotics at Cambridge, and Thomas George Thuruthel, a lecturer in robotics at University College London, describe the hand and its novel way of sensing touch.

The researchers show the hand detects and localises even light human touch, and detects the bending of the fingers. It can also work out temperature and humidity levels, through changes in the electrical field around it.