Here’s a party trick: Try opening a bottle of water using your thumb and pointer finger while holding it without spilling. It sounds simple, but the feat requires strength, dexterity, and coordination. Our hands have long inspired robotic mimics, but mechanical facsimiles still fall far short of their natural counterparts.
To Aude Billard and colleagues at the Swiss Federal Institute of Technology, trying to faithfully recreate the hand may be the wrong strategy. Why limit robots to human anatomy?
Billard’s team has now developed a prototype similar to Thing from The Addams Family.
Mounted on a robotic arm, the hand detaches at the wrist and transforms into a spider-like creature that can navigate nooks and crannies to pick up objects with its finger-legs. It then skitters on its fingertips back to the arm while holding on to its stash.
At a glance, the robot looks like a human hand. But it has an extra trick up its sleeve: It’s symmetrical, in that every finger is the same. The design essentially provides the hand with multiple thumbs. Any two fingers can pinch an object as opposing finger pairs. This makes complex single-handed maneuvers, like picking up a tube of mustard and a Pringles can at the same time, far easier. The robot can also bend its fingers forwards and backwards in ways that would break ours.
“The human hand is often viewed as the pinnacle of dexterity, and many robotic hands adopt anthropomorphic designs,” wrote the team. But by departing from anatomical constraints, the robot is both a hand and a walking machine capable of tasks that elude our hands.
Out of Reach
If you’ve ever tried putting a nut on a bolt in an extremely tight space, you’re probably very familiar with the limits of our hands. Grabbing and orienting tiny bits of hardware while holding a wrench in position can be extremely frustrating, especially if you have to bend your arm or wrist at an uncomfortable angle for leverage.
Sculpted by evolution, our hands can dance around a keyboard, perform difficult surgeries, and do other remarkable things. But their design can be improved. For one, our hands are asymmetrical and only have one opposable thumb, limiting dexterity in some finger pairs. Try screwing on a bottle cap with your middle finger and pinkie, for example. And to state the obvious, wrist movement and arm length restrict our hands’ overall capabilities. Also, our fingers can’t fully bend backwards, limiting the scope of their movement.
“Many anthropomorphic robotic hands inherit these constraints,” wrote the authors.
Partly inspired by nature, the team re-envisioned the concept of a hand or a finger. Rather than just a grasping tool, a hand could also have crawling abilities, a bit like octopus tentacles that seamlessly switch between movement and manipulation. Combining the two could extend the hand’s dexterity and capabilities.
Handy Upgrade
The team’s design process began with a database of standard hand models. Using a genetic algorithm, a type of machine learning inspired by natural selection, the team ran simulations on how different finger configurations changed the hand’s abilities.
By playing with the parameters, like how many fingers are needed to crawl smoothly, they zeroed in on a few guidelines. Five or six fingers gave the best performance, balancing grip strength and movement. Adding more digits caused the robot to stumble over its extra fingers.
In the final design, each three-jointed finger can bend towards the palm or to the back of the hand. The fingertips are coated in silicone for a better grip. Strong magnets at the base of the palm allow the hand to snap onto and detach from a robotic arm. The team made five- and six-fingered versions.
When attached to the arm, the hand easily pinches a Pringles can, tennis ball, and pen-shaped rod between two fingers. Its symmetrical design allows for some odd finger pairings, like using the equivalent of a ring and middle finger to tightly clutch a ball.
Other demos showcase its maneuverability. In one test, the robot twists off a mustard bottle cap while keeping the bottle steady. And because its fingers bend backwards, the hand can simultaneously pick up two objects, securing one on each side of its palm.
“While our robotic hand can perform common grasping modes like human hands, our design exceeds human capabilities by allowing any combination of fingers to form opposing finger pairs,” wrote the team. This allows “simultaneous multi-object grasping with fewer fingers.”
When released from the arm, the robot turns into a spider-like crawler. In another test, the six-fingered version grabs three blocks, none of which could be reached without detaching. The hand picks up the first two blocks by wrapping individual fingers around each. The same fingers then pinch the third block, and the robot skitters back to the arm on its remaining fingers.
The robot’s superhuman agility could let it explore places human hands can’t reach or traverse hazardous conditions during disaster response. It might also handle industrial inspection, like checking for rust or leakage in narrow pipes, or pick objects just out of reach in warehouses.
The team is also eyeing a more futuristic use: The hand could be adapted for prosthetics or even augmentation. Studies of people born with six fingers or those experimenting with an additional robotic finger have found the brain rapidly remaps to incorporate the digit in a variety of movements, often leading to more dexterity.
“The symmetrical, reversible functionality is particularly valuable in scenarios where users could benefit from capabilities beyond normal human function,” said Billard in a press release, but more work is needed to test the cyborg idea.
