Energy Harvesting

Vibration-Powered Robots the Size of the World’s Smallest Ant

Researchers at Georgia Tech have created a new type of tiny 3D-printed robot. The robot harnesses the vibration from piezoelectric actuators, ultrasound sources or even tiny speakers to move

The researchers speculate that in the future swarms of these “micro-bristle-bots” might work together to detect environmental changes, move materials, or one day even repair injuries inside the human body.

The prototype robots respond to different vibration frequencies depending upon their configurations. This custom configuring lets researchers control individual bots by adjusting the vibration.

At about two millimeters long, roughly the dimensions of the world’s smallest ant, the bots can reportedly cover four times their own length in a second despite the physical limitations of their diminutive size.

“We are working to make the technology robust, and we have a lot of potential applications in mind,” said Azadeh Ansari, an assistant professor in the School of Electrical and Computer Engineering at the Georgia Institute of Technology. “We are working at the intersection of mechanics, electronics, biology and physics. It’s a very rich area and there’s a lot of room for multidisciplinary concepts.”

The Journal of Micromechanics and Microengineering has accepted a paper describing the micro-bristle-bots for publication.

The research received the financial support of a seed grant from Georgia Tech’s Institute for Electronics and Nanotechnology. In addition to Ansari, the research team includes George W. Woodruff School of Mechanical Engineering Associate Professor Jun Ueda and graduate students Zhijian (Chris) Hao and DeaGyu Kim.

The micro-bristle-bots are made up of a piezoelectric actuator glued to a polymer body that is fabricated with 3D-printing using two-photon polymerization lithography (TPP).

No available batteries are small enough to fit onto the bot. Therefore, the actuator generates vibration and is powered externally.

The vibrations to power actuator can also come from a piezoelectric shaker beneath the surface upon which the robots move from a sonar/ultrasound source, or even from a tiny acoustic speaker. The vibrations induce the springy legs to move up and down, propelling the micro-bot forward.

Each robot can be made to respond to different vibration frequencies depending on its leg size, diameter, design, and overall geometry. The vibration amplitude controls the speed that micro-bots move accross a surface.

“As the micro-bristle-bots move up and down, the vertical motion is translated into a directional movement by optimizing the design of the legs, which look like bristles,” explained Ansari. “The legs of the micro-robot are designed with specific angles that allow them to bend and move in one direction in resonant response to the vibration.”

The TPP process polymerizes a monomer resin material. Once the portion of the resin block exposed to the ultraviolet light has been chemically developed, the remainder can be washed away, leaving the desired robotic structure.

“It’s writing rather than traditional lithography,” Ansari explained. “You are left with the structure that you write with a laser on the resin material. The process now takes quite a while, so we are looking at ways to scale it up to make hundreds or thousands of micro-bots at a time.”

Some of the newly developed robots feature four legs, while others have six. First, author DeaGyu Kim made hundreds of the tiny structures to find the ideal configuration.

The piezoelectric actuators use the material lead zirconate titanate (PZT). They vibrate when electric voltage is applied to them. In reverse, they can also be used to produce a voltage, when they are vibrated, a capability the micro-bristle-bots could utilize to power onboard sensors when external vibrations set their actuators in motion.

Ansari and her team are attempting to add a steering capability to the robots by merging two slightly different micro-bristle-bots together.

With each of the joined micro-bots responding to different vibration frequencies, the combination could be steered (at least in theory) by varying the frequencies and amplitudes.

“Once you have a fully steerable micro-robot, you can imagine doing a lot of interesting things,” she said.

Other researchers have developed micro-robots that use magnetic fields to induce movement, Ansari noted. While magnetic fields are useful for moving entire swarms simultaneously, such forces cannot easily be used to address individual robots in a swarm.

The micro-bristle-bots that Ansari and her team created are believed to be the smallest robots made so far that are powered by vibration. They measure about 2mm in length, 1.8mm wide and 0.8mm thick, and weigh about 5mg.

The 3D printer can produce smaller robots. However, they found that with a reduced mass, the adhesion forces between the tiny devices and a surface can become very large. Sometimes, the micro-bots cannot be separated from the tweezers that first pick them up from the 3D printer.

Ansari and her team have constructed a “playground” in which multiple micro-bots can move as the researchers learn more about what their capabilities. They are also interested in developing jumping and swimming micro-bots.

“We can look at the collective behavior of ants, for example, and apply what we learn from them to our little robots,” she added. “These micro-bristle-bots walk nicely in a laboratory environment, but there is a lot more we will have to do before they can go out into the outside world.”

Fabrication of the micro-bots was performed at the Georgia Tech Institute for Electronics and Nanotechnology, a member of the National Nanotechnology Coordinated Infrastructure, which is supported by the National Science Foundation through grant ECCS-1542173.

Citation

Kim, D., Hao, Z., Ueda, J., and Ansari, A., “A 5mg micro-bristle-bot fabricated by two-photon lithography,” Journal of Micromechanics and Microengineering, 2019. https://doi.org/10.1088/1361-6439/ab309b

Georgia Institute of Technology
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