Researchers Develop World's Smallest Programmable Autonomous Robot

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A team of scientists from the University of Pennsylvania and the University of Michigan has developed the world's smallest, fully programmable autonomous robot. The robot measures only 200 µm x 300 µm x 50 µm, but can still perceive and react to its environment independently. The robot is powered by tiny solar cells and is equipped with an ion drive for swimming locomotion.

The researchers from both universities have packed a lot of technology into the tiny robot, as they write in the study “Microscopic robots that sense, think, act, and compute,” which was published in Science Robotics. The heart of the robot is a computer developed by David Blaauw, a professor at the University of Michigan. He holds the record for the smallest computer in the world. Marc Miskin, assistant professor at the University of Pennsylvania and head of the microrobot project, and Blaauw first met five years ago at a Defense Advanced Research Projects Agency (DARPA) event and realized that Blaauw's tiny computer was perfect for a microrobot.

Microcomputer for a Microrobot

However, it was not easy to bring the microcomputer and the robot into harmony so that they would function together without problems. The power supply, in particular, proved to be difficult, as it had to keep the robot self-sufficient. The scientists use solar cells that generate only 75 nanowatts of power. That's more than 100,000 times less than a smartwatch needs, explains Blaauw. This made it necessary to revise the circuits of the existing microcomputer so that it could operate with extremely low voltages. The team succeeded in reducing the computer's power consumption by a factor of 1000.

However, the solar cells take up most of the robot's space. Consequently, little room was left for the processor and memory, so they could not be enlarged arbitrarily. The researchers got around this by compressing the computer programming to fit the program into the available limited memory. “We had to completely rethink the instructions of the computer program and condense what would conventionally require many instructions for drive control into a single special instruction to shorten the program length so that it would fit into the robot's tiny memory space,” says Blaauw.

The programming and transmission of the program to the computer is done via light pulses. Each robot has an individual address through which programming and transmission takes place. Robots can thus be programmed for different tasks to achieve a common result together in a swarm.

The robot's electronics also include temperature sensors that can measure the ambient temperature with an accuracy of up to one-third of a degree. The robot can thus detect and report temperatures and, for example, move towards or away from rising temperatures. This makes it possible, for example, to measure the temperature of a cell. Temperature is considered an indicator of cell health. This allows the health status of individual cells to be monitored.

The robot dances the measured temperature. Movements are triggered in the robot via an instruction, in which the temperature is encoded. The researchers then decode it via a microscope. This type of communication is similar to that of honeybees, which pass on information about dancing movements to their conspecifics.

Ion Drive Without Mechanical Components

To be able to move the robot in a liquid at all, the researchers had to develop a special drive concept, because, due to its tiny size, such a robot is exposed to forces that depend on volume, such as gravity and inertia. For robots compressed to micrometers, forces related to the surface, such as resistance and viscosity, take over. Accordingly, “progress in water is like progress in tar,” explains Miskin. The scientists therefore discarded mechanical drives with limbs, which are difficult to scale down to micrometer size because they could also break too easily.

The researchers therefore opted for an ion drive, which works entirely without mechanical parts. Instead, an electric field is generated that emits ions into the liquid surrounding the robot, presses on nearby liquid molecules, and sets the liquid around the robot in motion. “It's like the robot is in a flowing river,” says Miskin, “but the robot also causes the river to move.”

The effect can be adjusted by changing the electric field. The robot can thus move in complex patterns at a speed of up to one body length per second. The drive system is also very robust because it does not require mechanics. Microrobots equipped with it can be captured with a micropipette and transferred from one biological sample to another without damaging the robot.

The robot can thus move in a liquid for several months, provided it captures light via the solar cells. Illumination by LEDs provides the necessary energy. The robot is not controlled from the outside via magnetic fields, light, or radio waves. The tiny computer, the ion drive, and the solar cells give it the ability to be completely autonomous. The researchers worked for a total of five years on the development of the autonomous microrobot.

Costs of One US Cent

“This is really just the first chapter,” says Miskin. “We've shown that you can put a brain, a sensor, and a motor into something almost too small to see, and that it can survive and function for months. Once you have that foundation, you can add all sorts of intelligence and functionality. It opens the door to a whole new future for microrobotics.”

Future microrobots could become even more powerful, implement more complex programs, include new sensors, and move faster to navigate in more complex environments, the scientists say. The current platform shows that this is also possible at low cost: the current robot can be manufactured for a single US cent.

(olb)