Do a search for ‘robot hand’ online and you’ll soon come across mechanical metal constructions with humming actuators. “It gives you a queasy feeling. They look like claws”, says Professor Jo Geraedts. His engineering graduate, Rob Scharff, made a friendlier version in the first ‘soft robotics’ project at Delft University of Technology.
Robot hands often resemble cold claws, and that’s not so strange at all. Robot development started in electromechanical engineering, where researchers tried to copy movements by means of actuators and springs, ratchets and screws. That led to complicated constructions. “The literature mentions hands with twenty actuators”, says Geraedts.
About ten years ago, researchers started wondering if that couldn’t be done differently, says the mechatronic design professor. 3D printing emerged, with which is became possible to print complex structures in layers just 10 micrometres high, layer after layer, using materials with various properties, such as rigidity. Another development concerned the use of techniques drawn from nature. An elephant, for instance, has muscles in its trunk that are coiled like a helix. By contracting those muscles, it can twist its trunk in various ways. Scharff combined those two things, emulating that effect through 3D printing.
“By rotating a bellows over a helix, you can create a wrist-like rotation using air pressure”, Scharff says. In soft robotics, control is based on force, not position. “When you grab something, you stop at a certain exerted force instead of at a certain location”, Scharff explains. The thing is to emulate the human sense of touch. That has big advantages compared to mechanical control when grasping objects. “Especially if an object is slightly bigger or is situated a bit more to the left or right”, Scharff says. It is also safer. “Using soft materials and force-controlled movements facilitates human-robot collaboration.
You can even touch the robot. And – as in the case of my graduation – shake its hand.”
Professor Jo Geraedts: “If it is dark blue and it looks like a hand, people will say: wow!”
The dark blue, flexible hand that Scharff developed in collaboration with the Belgian company Materialise contains air chambers. If you squeeze those, the pressure increases. The robot ‘feels’ that you are shaking his hand. The firmer your grip, the higher the pressure in its air chambers, and the firmer it ‘squeezes’ back. All movement happens by means of air, using a compressor. “So, you don’t need any electronics in that hand, which also makes it possible to work with fluids and sand”, Geraedts says. Possible applications include active orthotic devices, a glove for example. “If it’s a thing with five shiny metal claws that makes noises, it just doesn’t feel right. If it’s dark blue and looks like an actual hand, people will say: ‘wow!’”