Researchers at MIT, USA, have developed microrobots the size of insects that work with the help of artificial muscles of low voltage and high power. The devices operate at 75% less voltage and are capable of carrying 80% more payload during flight.
The smooth actuators move the robot’s wings at high speed, giving the bot the agility similar to a mosquito that can fly in swarms to pollinate a field of crops or search for survivors under the rubble of a collapsed building.
“People tend to think that lightweight robots aren’t as capable as their rigid brethren. Now, we’ve demonstrated that these bots, weighing less than a gram, can fly and hover much longer while consuming almost no energy,” explains electrical engineering professor Kevin Chen, co-author of the study.
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artificial muscles
The rectangular microrobot weighs less than a coin and has only four sets of wings activated by a soft actuator. These “artificial muscles” have layers of elastomer sandwiched between two ultra-thin electrodes, rolled into a flexible cylinder. When voltage is applied to the actuator, the electrodes compress the elastomer and this mechanical stress causes the wings to beat non-stop.
During laboratory tests, scientists were able to create an actuator with 20 layers, each 10 micrometers thick — nearly the diameter of a red blood cell. In the device coating process, the elastomer is poured onto a flat surface rotating rapidly, causing centrifugal force to pull the film out, making it thinner.
“This process creates a lot of air bubbles, that’s why we developed an aspiration system that works right after the coating by rotation, with the elastomer still wet. Removing these defects increases the actuator’s power by more than 300% and significantly improves its service life,” adds Chen.
ultra thin electrodes
The researchers manufactured ultra-thin electrodes, made up of carbon nanotubes 50,000 times smaller than the diameter of a human hair. High concentrations of these nanotubes increase the power of the actuator and reduce the voltage required for its operation.
To circumvent the material’s curing time, scientists have found that baking each layer for a few minutes, immediately after the nanotubes are transferred to the elastomer, reduces the drying interval as more layers are added to the device.
“The first time I asked my student to make a multilayer actuator, upon reaching 12 ranges, he had to wait two days to fully cure. This made the entire process unfeasible, especially when one intends to manufacture equipment on a larger scale,” says Chen.
Multilayer
Science is already working on the development of artificial muscles that consume little energy to equip miniaturized robots. With this improved technique, the researchers created an artificial muscle containing 20 layers that needs less than 500 volts to function. Even with this reduced amount of electrical energy, the device can lift objects almost three times its own weight.
In addition, the microrobot was also able to remain hovering in the air for more than 20 seconds without losing stability, which, according to scientists, is a record for the category. The multi-layer actuator still remained working without any problems even after being actuated for more than 2 million cycles.
“Developing an artificial muscle of just 10 micrometers is exciting, but we are hoping to reduce that thickness to less than 1 micrometer, which could open many doors for creating more efficient robots the size of insects we find in nature,” he concludes. Kevin Chen.
