Researchers at Stanford University designed a spring-assisted actuator that could help powered prostheses use a fraction of the energy previously required. Standard electric motors were designed for steady, ongoing activities like running a compressor or spinning a conveyor belt and can waste a lot of energy when making more complicated movements required by prosthetic devices. With more efficient motors, recharging frequency would be reduced.
The new method augments electric motors to make them much more efficient at performing dynamic movements through a new type of actuator, a device that uses energy to make things move.
“Rather than wasting lots of electricity to just sit there humming away and generating heat, our actuator uses these clutches to achieve the very high levels of efficiency that we see from electric motors in continuous processes, without giving up on controllability and other features that make electric motors attractive,” said Steve Collins, PhD, associate professor of mechanical engineering and senior author of the paper.
The actuator works by harnessing the ability of springs to produce force without using energy; springs resist being stretched out and try to rebound to their natural length when released. When the actuator is lowering something heavy, the springs engage and stretch, taking some of the load off the motor. Then, by locking the springs in the stretched-out position, that energy can be stored to assist the motor in a later task.
The key to engaging and disengaging the springs quickly and efficiently is a series of electroadhesive clutches. Each rubber spring is sandwiched between two clutches: one that connects the spring to the joint to assist the motor and one that locks the spring in a stretched position when it’s not being used.
The clutches consist of two electrodes—one attached to the spring and one attached to the frame or motor—that slide smoothly past each other when they aren’t active. To engage a clutch, the researchers apply a large voltage to one of its electrodes. “They’re lightweight, they’re small, they’re really energy efficient, and they can be turned on and off rapidly,” said Erez Krimsky, PhD, lead author of the paper. “And if you have lots of clutched springs, it opens up all these exciting possibilities for how you can configure and control them to achieve interesting outcomes.”
The open-access study, “Elastic energy-recycling actuators for efficient robots,” was published in Science Robotics.
To watch a video showing and explaining the new actuator, visit the Stanford Biomechanics Lab.
Editor’s note: This story was adapted from materials provided by Stanford University.
