Science

Engineers design flexible ‘skeletons’ for soft, muscle-powered robots

MIT engineers have developed a brand new spring (proven in Petri dish) that maximizes the work of pure muscle tissue. When dwelling muscle tissue is connected to posts on the corners of the gadget, the muscle’s contractions pull on the spring, forming an efficient, pure actuator. The spring can function a “skeleton” for future muscle-powered robots. Credit: Felice Frankel

Our muscle tissue are nature’s good actuators—units that flip power into movement. For his or her measurement, muscle fibers are extra highly effective and exact than most artificial actuators. They’ll even heal from injury and develop stronger with train.

For these causes, engineers are exploring methods to energy robots with pure muscle tissue. They’ve demonstrated a handful of “biohybrid” robots that use muscle-based actuators to energy synthetic skeletons that stroll, swim, pump, and grip. However for each bot, there is a very completely different construct and no basic blueprint for how you can get probably the most out of muscle tissue for any given robotic design.

Now, MIT engineers have developed a spring-like gadget that could possibly be used as a fundamental skeleton-like module for nearly any muscle-bound bot. The brand new spring, or “flexure,” is designed to get probably the most work out of any connected muscle tissues. Like a leg press that is match with simply the correct amount of weight, the gadget maximizes the quantity of motion {that a} muscle can naturally produce.

The researchers discovered that once they match a hoop of muscle tissue onto the gadget, very like a rubber band stretched round two posts, the muscle pulled on the spring reliably and repeatedly and stretched it 5 instances extra, in contrast with different earlier gadget designs.

The staff sees the flexure design as a brand new constructing block that may be mixed with different flexures to construct any configuration of synthetic skeletons. Engineers can then match the skeletons with muscle tissues to energy their actions.

“These flexures are like a skeleton that people can now use to turn muscle actuation into multiple degrees of freedom of motion in a very predictable way,” says Ritu Raman, the Brit and Alex d’Arbeloff Profession Improvement Professor in Engineering Design at MIT. “We are giving roboticists a new set of rules to make powerful and precise muscle-powered robots that do interesting things.”

Raman and her colleagues report the small print of the brand new flexure design in a paper showing as we speak within the journal Superior Clever Programs. The examine’s MIT co-authors embody Naomi Lynch ’12, SM ’23; undergraduate Tara Sheehan; graduate college students Nicolas Castro, Laura Rosado, and Brandon Rios; and professor of mechanical engineering Martin Culpepper.

Muscle pull

When left alone in a petri dish in favorable circumstances, muscle tissue will contract by itself however in instructions that aren’t totally predictable or of a lot use.

“If the muscle is not attached to anything, it will move a lot, but with huge variability, where it’s just flailing around in the liquid,” Raman says.

Engineers usually connect a band of muscle tissue between two small, versatile posts to get a muscle to work like a mechanical actuator. Because the muscle band naturally contracts, it may possibly bend the posts and pull them collectively, producing some motion that might ideally energy a part of a robotic skeleton. Nonetheless, in these designs, muscle tissue have produced restricted motion, primarily as a result of the tissues are so variable in how they contact the posts.

Relying on the place the muscle tissue are positioned on the posts and the way a lot of the muscle floor is touching the submit, the muscle tissue might reach pulling the posts collectively however, at different instances, might wobble round in uncontrollable methods.

Raman’s group seemed to design a skeleton that focuses and maximizes a muscle’s contractions no matter precisely the place and the way it’s positioned on a skeleton to generate probably the most motion in a predictable, dependable manner.

“The question is: How do we design a skeleton that most efficiently uses the force the muscle is generating?” Raman says.

The researchers first thought-about the a number of instructions {that a} muscle can naturally transfer. They reasoned that if a muscle is to drag two posts collectively alongside a particular course, the posts must be linked to a spring that solely permits them to maneuver in that course when pulled.

“We need a device that is very soft and flexible in one direction and very stiff in all other directions so that when a muscle contracts, all that force gets efficiently converted into motion in one direction,” Raman says.

Tender flex

Because it seems, Raman discovered many such units in Professor Martin Culpepper’s lab. Culpepper’s group at MIT specializes within the design and fabrication of machine parts, similar to miniature actuators, bearings, and different mechanisms that may be constructed into machines and methods to allow ultraprecise motion, measurement, and management for all kinds of purposes.

Among the many group’s precision machined parts are flexures—spring-like units, usually comprised of parallel beams, that may flex and stretch with nanometer precision.

“Depending on how thin and far apart the beams are, you can change how stiff the spring appears to be,” Raman says.

She and Culpepper teamed as much as design a flexure particularly tailor-made with a configuration and stiffness to allow muscle tissue to contract and maximally stretch the spring naturally. The staff designed the gadget’s configuration and dimensions primarily based on quite a few calculations they carried out to narrate a muscle’s pure forces with a flexure’s stiffness and diploma of motion.

The flexure they in the end designed is 1/100 the stiffness of the muscle tissue itself. The gadget resembles a miniature, accordion-like construction, the corners of that are pinned to an underlying base by a small submit, which sits close to a neighboring submit that matches instantly onto the bottom.

Raman then wrapped a band of muscle across the two nook posts (the staff molded the bands from dwell muscle fibers that they grew from mouse cells), and measured how shut the posts had been pulled collectively because the muscle band contracted.

The staff discovered that the flexure’s configuration enabled the muscle band to contract largely alongside the course between the 2 posts. This centered contraction allowed the muscle to drag the posts a lot nearer collectively—5 instances nearer—in contrast with earlier muscle actuator designs.

“The flexure is a skeleton that we designed to be very soft and flexible in one direction and very stiff in all other directions,” Raman says. “When the muscle contracts, all the force is converted into movement in that direction. It’s a huge magnification.”

The staff discovered they might use the gadget to measure muscle efficiency and endurance exactly. Once they various the frequency of muscle contractions (for example, stimulating the bands to contract as soon as versus 4 instances per second), they noticed that the muscle tissue “grew tired” at increased frequencies and did not generate as a lot pull.

“Looking at how quickly our muscles get tired and how we can exercise them to have high-endurance responses—this is what we can uncover with this platform,” Raman says.

The researchers at the moment are adapting and mixing flexures to construct exact, articulated, and dependable robots, powered by pure muscle tissue.

“An example of a robot we are trying to build in the future is a surgical robot that can perform minimally invasive procedures inside the body,” Raman says. “Technically, muscles can power robots of any size, but we are particularly excited in making small robots, as this is where biological actuators excel in terms of strength, efficiency, and adaptability.”

Extra data:
Naomi Lynch et al, Enhancing and Decoding the Efficiency of Muscle Actuators with Flexures, Superior Clever Programs (2024). DOI: 10.1002/aisy.202300834

This story is republished courtesy of MIT News (web.mit.edu/newsoffice/), a preferred website that covers information about MIT analysis, innovation and instructing.

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