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Actuator Vibration Moves Tiny 3D-Printed Robots
September 2019

Researchers and scientists around the world continue to make significant advances in the field of robotics from large ones designed for industry to small ones which could be deployed in disaster areas to eliminate the potential danger to human responders and investigators.

A micro-bristle-bot is shown next to a U.S. penny for size comparison. Photo: Allison Carter

Now, according to information provided by the Georgia Institute of Technology (Georgia Tech), researchers have created a new type of tiny 3D-printed robot that moves by harnessing vibration from piezoelectric actuators, ultrasound/sonar sources or even tiny speakers. Swarms of these “micro-bristle-bots” might work together to sense environmental changes, move materials – or perhaps one day repair injuries inside the human body.

According to Azadeh Ansari, an assistant professor in the School of Electrical and Computer Engineering at the Georgia Tech, other researchers have worked on micro-robots that use magnetic fields to produce movement. While a useful approach for moving entire swarms simultaneously, she noted, magnetic forces cannot easily be used to address individual robots within a swarm. The new micro-bristle-bots created by Prof. Ansari and her team are believed to be the smallest robots powered by vibration.

The prototype robots, approximately two millimeters in length, 1.8 millimeters wide and 0.8 millimeters thick, and weigh about five milligrams, respond to different vibration frequencies depending on their configurations, allowing researchers to control individual bots by adjusting the vibration. The new micro-bristle-bots can cover four times their own length in a second despite the physical limitations of their small size.

“We are working to make the technology robust, and we have a lot of potential applications in mind,” noted Prof. Ansari. “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.”

Supported by a seed grant from Georgia Tech’s Institute for Electronics and Nanotechnology, the researchers describe their work in a paper, “A 5mg micro-bristle-bot fabricated by two-photon lithography,” published in the Journal of Micromechanics and Microengineering. In addition to Prof. Ansari, the research team includes George W. Woodruff School of Mechanical Engineering Associate Professor Jun Ueda and graduate students DeaGyu Kim and Zhijian (Chris) Hao.

As described in their paper, the micro-bristle-bots consist of a piezoelectric actuator glued onto a polymer body that is 3D-printed using two-photon polymerization lithography (TPP), a technique that polymerizes a monomer resin material. The actuator, externally powered as its physical size is too small to allow a power source to fit on the body, generates the vibration frequencies required for movement; however, the vibrations can also come from a piezoelectric shaker beneath the surface on which the robots move, from an ultrasound/sonar source, or even from a tiny acoustic speaker.

Demonstrated in their presentational video, the vibrations move the springy legs up and down, propelling the micro-bot forward. Each robot can be designed to respond to different vibration frequencies depending on leg size, diameter, design and overall geometry. The amplitude of the vibrations controls the speed at which the micro-bots move.

“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 Prof. 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 piezoelectric actuators, which use the material lead zirconate titanate (PZT), vibrate when electric voltage is applied to them. In reverse, they can also be used to generate a voltage, when they are vibrated, a capability the micro-bristle-bots could use in the future to power up onboard sensors when they are actuated by external vibrations.

The micro-bot fabrication was performed at the Georgia Tech Institute for Electronics and Nanotechnology, a member of the National Nanotechnology Coordinated Infrastructure, which is supported by a grant from the National Science Foundation.

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