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Stanford invents super-efficient 'spring-powered' actuator for robots

In the rapidly evolving worlds of robotics and bionics, power efficiency is a major limiting factor. Traditional electric motors waste huge amounts of energy when tasked with dynamic, complex movements - draining batteries and restricting capabilities.

However, researchers at Stanford University have invented a game-changing solution: a spring-powered actuator that can augment electric motors to make them vastly more energy-efficient for dynamic tasks like navigating, lifting, or advanced locomotive functions.



Published in the journal Science Robotics, the actuator combines the precision of an electric motor with a series of rubber springs and electro-adhesive clutches. This ingenious design allows it to recapture energy from movements like lowering a heavy load, store that potential energy temporarily in the stretched springs, and then deploy it for other tasks - reducing overall power draw by up to 97% compared to conventional electric motors alone.

"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," explained Steve Collins, associate professor of mechanical engineering and senior author of the study.

At the heart of the actuator are those electro-adhesive clutches - low-power mechanisms that can rapidly lock and release the rubber springs. Each spring has two clutches, one connecting it to the motor to assist movements, and another that locks it in a stretched position when energy storage is needed. Applying a voltage causes the clutch electrodes to bind together with an audible "click", capturing the spring force, while grounding the electrodes releases it.

"They're lightweight, they're small, they're really energy efficient, and they can be turned on and off rapidly," said Erez Krimsky, the paper's lead author who developed the technology as a PhD student in Collins' lab. "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 prototype actuator built by the researchers has six clutched springs that can be engaged in 64 different combinations to handle a variety of motion tasks. In tests simulating rapid acceleration, changing loads, and steady movements, it consistently outperformed conventional electric motors by over 50% efficiency, with that 97% best-case scenario.

The ramifications for robotics and bioengineering could be profound. Powered prosthetics, exoskeletons, and other robotic assistive devices that currently struggle with limited battery life could operate for significantly longer on a single charge. And mobile robots sent into hazardous environments could work an entire day without needing to recharge, radically expanding their potential.

"If you don't need to constantly recharge them, they can have a much more significant impact for the people that use them," Krimsky said.

While the actuator currently takes a few minutes to calculate optimal spring configurations for new motion tasks, the researchers aim to develop machine learning systems that can process efficient movement strategies on the fly. They also have plans to commercialize the technology by spinning it out into a startup that manufactures the actuators.

"We think that the technology is really at a place where it's ready for commercial translation," Collins stated. "We'd be excited to try to spin this out from the lab and start a company to begin making these actuators for the robots of the future."

If widely adopted, Stanford's spring-powered actuator design could help propel robotics into a new era of enhanced mobility, autonomy and functionality across countless applications. By tackling energy efficiency head-on, it could be the breakthrough that allows robots to truly go the distance.

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