Microrobot collectives display versatile movement patterns
System capable of quick transitions between behaviors

Date:
April 26, 2022
Source:
Max Planck Institute for Intelligent Systems
Summary:
Collective behavior and swarm patterns are found everywhere
in nature.

Robots can also be programmed to act in swarms. Researchers have
developed collectives of microrobots, which they can move in every
formation they wish.



FULL STORY ========================================================================== Researchers at the Max Planck Institute for Intelligent Systems (MPI-IS), Cornell University and Shanghai Jiao Tong University have developed
collectives of microrobots which can move in any desired formation. The miniature particles are capable of reconfiguring their swarm behavior
quickly and robustly.

Floating on the surface of water, the versatile microrobotic discs can
go round in circles, dance the boogie, bunch up into a clump, spread
out like gas or form a straight line like beads on a string.


==========================================================================
Each robot is slightly bigger than a hair's width. They are 3D printed
using a polymer and then coated with a thin top layer of cobalt. Thanks to
the metal the microrobots become miniature magnets. Meanwhile, wire coils
which create a magnetic field when electricity flows through them surround
the setup. The magnetic field allows the particles to be precisely steered around a one- centimeter-wide pool of water. When they form a line, for instance, the researchers can move the robots in such a way that they
"write" letters in the water. The research project of Gaurav Gardi and
Prof. Metin Sitti from MPI-IS, Steven Ceron and Prof. Kirstin Petersen
from Cornell University and Prof.

Wendong Wang from Shanghai Jiao Tong University titled "Microrobot
Collectives with Reconfigurable Morphologies, Behaviors, and Functions"
was published inNature Communicationson April 26, 2022.

Collective behavior emerges from the interactions between the robots
Collective behavior and swarm patterns are found everywhere in nature. A
flock of birds exhibits swarm behavior, as does a school of fish. Robots
can also be programmed to act in swarms -- and have been seen doing
so quite prominently. A technology company recently presented a drone
lightshow that won the company a Guinness World Record by programming
several hundred drones and flying them side-by-side, creating amazing
patterns in the night sky. Each drone in this swarm was equipped with computational power steering it in every possible direction. But what if
the single particle is so tiny that computation isn't an option? When
a robot is just 300 micrometers wide, one cannot program it with an
algorithm.

Three different forces are at play to compensate for the lack of
computation.

One is the magnetic force. Two magnets with opposite poles attract. Two identical poles repel each other. The second force is the fluid
environment; the water around the discs. When particles swim in a swirl of water, they displace the water and affect the other surrounding particles
in the system.

The speed of the swirl and its magnitude determine how the particles
interact.

Thirdly, if two particles float next to each other, they tend to drift
towards each other: they bend the water surface in such a way that they
slowly come together. Scientists and cereal lovers call this the cheerio effect: if you let two cheerios float on milk, they will soon bump into
each other. On the flip side, this effect can also cause two things to
repel each other (try a hairpin and a cheerio).

Three forces allow for reconfigurability The scientists use all three
forces to create a coordinated, collective pattern of motion for several
dozen microrobots as one system. A video (https:// youtu.be/q91AWmTBzG8)
shows how the scientists steer the robots through a parcour, displaying
the formation that best suits the obstacle course, e.g.

when they enter a narrow passage, the microrobots line up in single file
and disperse again when they come out. The scientists can also make
the robots dance, alone or as pairs. Additionally, they show how they
put a tiny plastic ball into the water container and then aggregate the
robots into a clump to push the floating ball along. They can place the
tiny particles inside two gears and move the particles in a way that
causes both gears to rotate. A more ordered pattern is also possible
with each particle keeping an identical distance to its neighbor. All
these different locomotion modes and formations are achieved through
external computation: an algorithm is programmed to create a rotating
or oscillating magnetic field which triggers the desired movement and reconfigurability.

"Depending on how we change the magnetic fields, the discs behave in a different way. We are tuning one force and then another until we get the movement we want. If we rotate the magnetic field within the coils too vigorously, the force which is causing the water to move around is too
strong and the discs move away from each other. If we rotate too slow,
then the cheerio effect which attracts the particles is too strong. We
need to find the balance between the three," Gaurav Gardi explains. He
is a Ph.D. student in the Physical Intelligence department at MPI-IS
and one of the two lead authors of the publication together with Steven
Ceron from Cornell University.

A model for future biomedical and environmental applications The future scenario for such microrobotic collectives is to go even smaller.

"Our vision is to develop a system that is even tinier, made of particles
only one micrometer small. These collectives could potentially go inside
the human body and navigate through complex environments to deliver
drugs, for instance, to block or unblock passages, or to stimulate a hard-to-reach area," Gardi says.

"Robot collectives with robust transitions between locomotion behaviors
are very rare. However, such versatile systems are advantageous to
operate in complex environments. We are very happy we succeeded in
developing such a robust and on-demand reconfigurable collective. We see
our research as a blueprint for future biomedical applications, minimally invasive treatments, or environmental remediation," adds Metin Sitti,
who leads the Physical Intelligence Department and is a pioneer in the
field of small-scale robotics and physical intelligence.


========================================================================== Story Source: Materials provided by Max_Planck_Institute_for_Intelligent_Systems. Note: Content may be edited
for style and length.


========================================================================== Journal Reference:
1. Gaurav Gardi, Steven Ceron, Wendong Wang, Kirstin Petersen,
Metin Sitti.

Microrobot collectives with reconfigurable morphologies,
behaviors, and functions. Nature Communications, 2022; 13 (1) DOI:
10.1038/s41467-022- 29882-5 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/04/220426101643.htm

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