1 Closed-loop Control of Catalytic Janus Microrobots Max Sokolich David Rivas Zameer Hussain Shah Sambeeta Das

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Closed-loop Control of Catalytic Janus Microrobots

Max Sokolich, David Rivas, Zameer Hussain Shah, Sambeeta Das∗

Department of Mechanical Engineering, University of Delaware, Newark, DE 19717 USA

Abstract—We report a closed-loop control system for paramag-

netic catalytically self-propelled Janus microrobots. We achieve

this control by employing electromagnetic coils that direct the

magnetic ﬁeld in a desired orientation to steer the microrobots.

The microrobots move due to the catalytic decomposition of

hydrogen peroxide, during which they align themselves to the

magnetic torques applied to them. Because the angle between

their direction of motion and their magnetic orientation is a priori

unknown, an algorithm is used to determine this angular offset

and adjust the magnetic ﬁeld appropriately. The microrobots

are located using real-time particle tracking that integrates with

a video camera. A target location or desired trajectory can be

drawn by the user for the microrobots to follow.

Index Terms—micro-robots, magnetic-control, closed-loop,

computer-vision

I. INTRODUCTION

Microrobots are tiny machines designed to perform speciﬁc

tasks in complex environments. [1] These nanomachines hold

the key to the future of effective biomedicine and a clean en-

vironment. [2], [3] Microrobotics is still an infant technology,

and more fundamental and applied work is needed before its

widespread use. [4] On the fundamental side, understanding

the active motion of microrobots is of prime signiﬁcance.

Microrobots can be actuated by a chemical fuel such as

peroxide or by an external ﬁeld such as a magnetic ﬁeld or

light, etc. [5] Chemically powered microrobots have been the

center of attention since their discovery in 2004. [6] These

micromotors utilize fuel from their surroundings as a source

of energy to drive their motion. [7] Typically, these micron-

sized particles are equipped with a catalyst that can decompose

the fuel. In the classic design, polymeric microspheres are

half-coated with platinum to fabricate asymmetric particles,

also known as Janus colloids. [8] The non-symmetric nature

of these particles results in an asymmetric breakdown of

fuel molecules around the particle. This non-uniform reaction

around the particle results in an unequal pressure on the

particle that leads to its directional motion. [9]

Even though chemically propelled particles follow a tra-

jectory, their direction of motion is not controlled and often

approximates a random walk at long times due to thermal

rotational ﬂuctuations. To get control over the directionality,

it is a common practice to include a magnetic component in

a chemically powered micromotor. [11]This simple strategy

allows the chemically powered micromotors to move in a

speciﬁc direction under the inﬂuence of a magnetic ﬁeld.

Magnetic ﬁelds have been used to propel and steer micro-

robots for over a decade. [14] They offer a facile approach

for moving microrobots towards desired locations. Palacci

demonstrated that a light activated colloidal particle could be

steered magnetically to a colloidal particle and then transport it

to a targeted location. [15] Similarly, Baraban and co-workers

reported that homogeneous magnetic ﬁelds on the order of

milli-Teslas could be used to control the direction of motion

of Janus micromotors. [16] Weak magnetic ﬁelds have also

been shown to control the motion and localization of Pt-SiO2

Janus micromotors in 2D as well as 3D spaces. [17] In a more

advanced model of magnetically controlled navigation, Joseph

Wang’s group have developed smart microrobots capable of

autonomous navigation in complex environments and trafﬁc

scenarios. [18]

For practical applications such as targeted therapy and

micromanipulation, it is highly desired to precisely control

the microrobot motion from one point to another point.

[10] Attaining greater precision than with manual, open-

loop, control, can be attained by using an automated control

strategy. Automation is also advantageous due to its greater

reproducibility, predictability, and ease of use. Therefore, one

of the most attractive approaches for precise control over

microrobots is the so called closed-loop control also known

as feedback control. In closed-loop control the response is

continuously compared with the desired output and modiﬁed

to minimize any deviations. [20] Closed-loop control has been

utilized to control the motion of microrobots of different

shapes. [26] Khalil and co-workers have extensively studied

the closed-loop control of magnetically responsive chemically

propelled microjets. [21], [23] The authors controlled orienta-

tion of the microjets with external magnetic torques while the

linear motion towards a reference was controlled by a thrust

generated from the chemically produced oxygen bubbles and

a magnetic ﬁeld gradient. Similarly, Marino et al. [24] have

reported the closed-loop control studies of cylindrical-shaped

microbots. The authors presented different methods to control

the uncertainties in electromagnetic force generation and drag

forces. Recently, Jiang et al. [25] have developed a closed-loop

control system to control the motion of a vortex-like magnetic

microswarm. They employed commercial servo ampliﬁers to

improve the performance of their system. Interestingly, most of

the work published on the closed-loop control of microrobots

is done on particles of shapes that are a specialty of the group.

Since the most common form of catalytic microrobots is a

spherical Janus colloid, closed-loop control systems for these

particles is of particular importance.

In this work, we demonstrate a simple control algorithm

for transporting paramagnetic catalytic Janus micromotors to

target locations in the workspace. This is done using a custom

tracking program written in python, and the ModMag micro-

robotic manipulation device. The algorithm is also extended

towards more complicated trajectories. We demonstrate this

by drawing curved paths on the video display which the

microrobots follow.

arXiv:2210.11460v1 [cs.RO] 20 Oct 2022

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1Closed-loopControlofCatalyticJanusMicrorobotsMaxSokolich,DavidRivas,ZameerHussainShah,SambeetaDasDepartmentofMechanicalEngineering,UniversityofDelaware,Newark,DE19717USAAbstractWereportaclosed-loopcontrolsystemforparamag-neticcatalyticallyself-propelledJanusmicrorobots.Weachievethiscontrolbyemplo...

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1 Closed-loop Control of Catalytic Janus Microrobots Max Sokolich David Rivas Zameer Hussain Shah Sambeeta Das

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