Robots Flex Their New Muscles

Robots that stay firmly parked in one spot all day are the workhorses of today’s manufacturing facilities and warehouses. These machines are well-known for their ability to repetitively perform the same task over and over, day and night, with great precision and efficiency. But you might say that this first step into the world of robotics was the easy part. The next revolution in robotics will require the development of mobile machines that can nimbly interact with the world around them and adapt to unexpected situations.

The problem is that today’s robots tend to be big and clunky. This arises from the fact that the systems that power these machines are very unlike the sensitive and efficient systems that power biological organisms. One of the biggest issues is that the motors we use to actuate robotic systems are nothing like muscle tissue. Motors, by comparison, are heavy, bulky, inefficient, and lack adaptability. But that may soon begin to change, thanks to the work of a team led by researchers at the Federal Institute of Technology in Zurich.

They have developed a novel type of robotic leg that was inspired by the basic components that make up human legs. Composed of artificial muscles, joints, and tendons, these legs are far more efficient and dexterous than traditional robot legs powered by motors. It was shown that a robot equipped with these legs can walk, adapt to a wide variety of terrains, and even perform high jumps — all without requiring complex sensing instruments.

Called PELE, this robotic leg consists of a carbon fiber backbone, which is very strong yet keeps the leg very light. 3D-printed joints at the knee and hip allow the leg to move in a natural manner. But the key innovation in PELE is the muscles. These artificial muscles are composed of electrohydraulic actuators attached to the frame via artificial tendons. The muscles are arranged in extensor and flexor pairs to enable movement in two directions, much like real muscles.

Each artificial muscle is composed of a polymer bag filled with an oily liquid dielectric. Both sides of the bag are covered in electrodes. Different electric potentials are then applied to the electrodes on each side, which produces electrostatic forces that cause the electrodes on opposing sides to be drawn toward one another. That, in turn, squeezes the bag and moves the oil to one side, which shortens the bag’s length. This action is akin to the contraction of real muscle tissue.

When compared with a traditional electromagnetic motor, this new system consumes far less power — only 1.2 percent as much. That means robots using these muscles can operate for longer periods of time and carry less battery weight, to boot. Experiments also demonstrated that the artificial muscles can adapt to changing conditions much more easily than traditional motors. Rather than having to be fed precise angles of movement, the flexibility of the bags allows them to adapt to whatever comes their way.

There is still a lot of work to be done, however. The existing prototype leg is attached to a spinning rod and cannot move freely. But with some work, this system could be built into a quadrupedal or humanoid robot, and that could forever transform what is possible in the world of robotics.