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Developing Agile and Durable Microrobots in the U.S.

Image credits: news.mit.edu

MIT researchers have demonstrated diminutive drones that can zip around with bug-like agility and resilience, which could eventually perform these tasks. The soft actuators that propel these microrobots are very durable, but they require much higher voltages than similarly-sized rigid actuators. The featherweight robots can’t carry the necessary power electronics that would allow them to fly on their own.

Now, these researchers have pioneered a fabrication technique that enables them to build soft actuators that operate with 75% lower voltage than current versions while carrying 80% more payload. These soft actuators are like artificial muscles that rapidly flap the robot’s wings. This new fabrication technique produces artificial muscles with fewer defects, which dramatically extends the lifespan of the components and increases the robot’s performance and payload.

This opens up a lot of opportunities in the future for us to transition to putting 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 for the longest time with the smallest error during a hovering flight. The take-home message is that soft robots can exceed the performance of rigid robots.

– Kevin Chen, Head of Soft and Micro Robotics Laboratory, Research Laboratory of Electronics

The rectangular microrobot, which weighs less than one-fourth of a penny, has four sets of wings that are each driven by a soft actuator. These muscle-like actuators are made from layers of elastomer that are sandwiched between two very thin electrodes and then rolled into a squishy cylinder. When voltage is applied to the actuator, the electrodes squeeze the elastomer, and that mechanical strain is used to flap the wing.

The more surface area the actuator has, the less voltage is required. So, Chen and his team build these artificial muscles by alternating between as many ultrathin layers of elastomer and electrode as they can. As elastomer layers get thinner, they become more unstable.

For the first time, the researchers were able to create an actuator with 20 layers, each of which is 10 micrometres in thickness (about the diameter of a red blood cell). But they had to reinvent parts of the fabrication process to get there. One major roadblock came from the spin coating process. During spin coating, an elastomer is poured onto a flat surface and rapidly rotated, and the centrifugal force pulls the film outward to make it thinner.

If they perform a vacuuming process immediately after spin coating, while the elastomer was still wet, it removes the air bubbles. Then, they bake the elastomer to dry it. Removing these defects increases the power output of the actuator by more than 300% and significantly improves its lifespan

The researchers also optimised the thin electrodes, which are composed of carbon nanotubes, super-strong rolls of carbon that are about 1/50,000 the diameter of human hair. Higher concentrations of carbon nanotubes increase the actuator’s power output and reduce the voltage but dense layers also contain more defects.

After using this technique to create a 20-layer artificial muscle, they tested it against their previous six-layer version and state-of-the-art, rigid actuators. During liftoff experiments, the 20-layer actuator, which requires less than 500 volts to operate, exerted enough power to give the robot a lift-to-weight ratio of 3.7 to 1, so it could carry items that are nearly three times its weight.

As reported by OpenGov Asia, MIT researchers show robots are more widely adopted where populations become notably older, filling the gaps in an ageing industrial workforce. The research also showed age alone accounted for 35% of the variation between countries in their adoption of robots, with those having older workers far more likely to adopt the machines.

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