Artificial muscles could allow robots to lift 80 times their own weight
By David Szondy
September 10, 2013
It's a classic science fiction scene: an android is injured and its human-like exterior is laid bare to reveal the metallic gears and cables of its true mechanical nature. The future is, unsurprisingly, not likely to match this scenario as our ability to mimic biology with innovations like artificial muscles improves. The latest breakthrough in this field comes from the National University of Singapore’s Faculty of Engineering where researchers have developed a “robotic” muscle that extends like real muscle tissue to five times its original length, has the potential to lift 80 times its own weight and holds out the promise of smaller, stronger robots capable of more refined movements.
In the 1960s, John W. Campbell Jr, editor of Analog Science Fiction magazine, pointed out a problem with robots that still plagues engineers today. He outlined a scenario where a man is chased across rough country by a mad scientist’s horde of killer robots. The various models were stymied by obstacles that the man could overcome, such as sinking in mud or getting tangled in bushes, and that the only robots capable of keeping up with the man were so light and underpowered that he ended up tearing them apart with his bare hands.
The point is this: robots are weaklings. We tend to think of robots as mechanical Samsons that can bend steel in their claws, and many can. However, the powerhouse robots are also extremely heavy and use hydraulics for the heavy lifting. Pound for pound they’re actually very weak compared to a human, being capable of lifting only half their weight.
In addition, robots using gears and motors, pneumatics, or hydraulics lack fine control. They tend to move in jerks and have to pause between each move. This makes robots move in a, well, “robotic” fashion and this is why animatronic robots often look like they have a tic. It’s very difficult to make a robot capable of delicate, smooth movements.
One solution to this problem is biomimetics. In other words, by borrowing from the design work that nature has already done. Artificial muscles, which have been around for some years, are an example of this. Instead of electric motors or pumps to turn cams or push fluids, the artificial muscle is a material or device that expands and contracts the way real muscles do. The difference is that where muscles burn sugars, artificial muscles use electric fields, pneumatic bladders, ions, or heat.
The tricky bit with artificial muscles is that how strong they are depends on how far they can extend. The further the extension, the greater the strength. Currently, artificial muscles only extend about three times their original length. This limits not only strength, but the level of control, so movements powered by artificial muscles leave a lot to be desired.
Billed as a first in robotics, the NUS artificial muscle was developed by a four-person team Led by Dr Adrian Koh of the NUS Engineering Science Program and Department of Civil and Environmental Engineering. Its an example of an electroactive polymer. In this case, a dielectric elastomer based on rubber that changes shape when subjected to an electric field. Theoretically, such a polymer could extend to ten times its length and lift 500 times its own weight, though the current version isn’t anywhere near that limit.
"Our materials mimic those of the human muscle, responding quickly to electrical impulses instead of slowly for mechanisms driven by hydraulics," says Dr Koh. "Robots move in a jerky manner because of this mechanism. Now, imagine artificial muscles which are pliable, extendable and react in a fraction of a second like those of a human. Robots equipped with such muscles will be able to function in a more human-like manner – and outperform humans in strength."
Robots using artificial muscles would be a far cry from clanking mechanical men. They would be much more lifelike, capable of facial expression and precise, graceful movements. They would also have superhuman strength, yet weigh the same as a person.
In addition, the polymer may have more general applications in machines, such as cranes. An added bonus of the polymer is that is can convert and store energy, which means it’s possible to design robots that power themselves after charging for only minutes.
"Our novel muscles are not just strong and responsive," Dr Koh says. "Their movements produce a by-product – energy. As the muscles contract and expand, they are capable of converting mechanical energy into electrical energy. Due to the nature of this material, it is capable of packing a large amount of energy in a small package. We calculated that if one were to build an electrical generator from these soft materials, a 10 kg (22 lb) system is capable of producing the same amount of energy of a one-ton electrical turbine."
Dr Koh and his team have applied for a patent for the artificial muscle and are continuing work on it. They predict that within five years they could have a robot arm that is half the size and weight of a human arm, yet could win an arm wrestling match.
The results of the team’s research was presented in June at the 3rd International Conference on Electromechanically-Active Polymer Transducers and Artificial Muscles in Zurich, Switzerland.
Source: National University of Singapore