New technique improves the performance of flying microbots

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Researchers at the Massachusetts Institute of Technology have developed a new manufacturing technique that enables the production of flexible low voltage, high power density, high endurance actuators for aerial microrobots. Artificial muscles improve the robot’s payload and allow it to achieve best-in-class hover performance.

Artificial muscles with fewer defects

Flexible actuators operate at 75% lower voltage than current versions and carry 80% more payload. The artificial muscles produced by the manufacturing technique also have fewer defects, which prolongs the life of the components.

Kevin Chen is the D. Reid Weedon, Jr. ’41 assistant professor in the Department of Electrical and Computer Engineering. He is also the head of the Soft and Micro Robotics Laboratory of the Electronics Research Laboratory (RLE) and the main author of the research.

“This opens up many opportunities in the future for us to switch to power electronics on the microrobot. People tend to think that soft robots are not as capable as rigid robots. We demonstrate that this robot, weighing less than a gram, flies the longest with the smallest error during a hover. The take-home message is that flexible robots can exceed the performance of rigid robots, ”explains Chen.

The research was published in Advanced materials.

The rectangular robot weighs less than a quarter of a dime and has four sets of wings that are each driven by a flexible actuator. Muscle type actuators are made of elastomer layers located between two thin electrodes. When voltage is applied to the actuator, the electrodes squeeze the elastomer, resulting in mechanical stress that causes the wing to flap.

The team were able to create an actuator with 20 layers, each measuring 10 microns thick.

Centrifugal Coating Process

One of the biggest hurdles the team encountered was the spin coating process, which involves pouring an elastomer onto a flat surface and spinning quickly. The centrifugal force causes the film to be pulled out to become thinner.

“In this process, the air flows back into the elastomer and creates many microscopic air bubbles. The diameter of these air bubbles is barely 1 micrometer, so previously we kind of ignored them. But when you get thinner and thinner layers, the effect of air bubbles becomes stronger and stronger. This is traditionally the reason why people have not been able to make these very thin layers, ”says Chen.

By performing a vacuum process just after spin coating, air bubbles are removed and the elastomer can be baked to dry.

By removing these faults, the output power of the actuator is increased by more than 300%, and its service life is significantly improved.

The researchers used these techniques to create the 20-layered artificial muscle, which was then tested against their previous sx-layered version and state-of-the-art rigid actuators.

The 20-layer actuator, requiring less than 500 volts to operate, exerted enough power to give the robot a 3.7 to 1 weight-to-thrust ratio, meaning it could haul things around three times its weight. .

The team also successfully completed a 20-second hover, which Chen says is the longest ever recorded by a subgram robot.

“Two years ago we created the strongest actuator and it could barely fly. We started to wonder if soft robots could compete with rigid robots? We observed one defect after another, so we kept working and solved one manufacturing problem after another, and now the soft actuator performance is catching up. They’re even a little better than the state-of-the-art rigs. And there are still a number of manufacturing processes in materials science that we don’t understand. So I’m very excited to continue reducing the actuation voltage, ”he says.

The team is now looking to more precise methods than spin coating to refine the layers. Chen hopes the thickness can be reduced to just 1 micron.


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