OctoMag: An electromagnetic system for 5-DOF wireless micromanipulation.
ABSTRACT We demonstrate five-degree-of-freedom (5-DOF) wireless magnetic control of a fully untethered microrobot with a magnetic steering system we call OctoMag. Although only occupying a single hemisphere, this system is capable of isotropically applying forces on the order of 1-40 μN with unrestricted control of the 2 orienting DOF. These capabilities are enabled through the use of soft-magnetic-cores which provide an increase of approximately 20× that of air cores in magnetic-field strength, but comes at the cost of more complicated interactions between coils. We propose a modeling mechanism that assumes the field contributions of the individual currents superimpose linearly when using cores with large linear regions and negligible hysteresis. When designing the system, the locations and quantity of electromagnets were optimized with regards to the force generation in the worst-case direction predicted by the model. The resultant system is capable of both open and closed-loop operation over a workspace of 4 cm3. OctoMag was primarily designed for the control of intraocular microrobots for delicate retinal procedures, but also has potential uses in other medical applications or micromanipulation under an optical microscope.
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ABSTRACT: Recently, the locomotion of a microrobot wirelessly actuated by electromagnetic actuation systems has been studied in many ways. Because of the inherent characteristics of an electromagnetic field, however, the magnetic field of each coil in the electromagnetic actuation system induces magnetic field interferences, which can distort the desired electromagnetic field, preventing the microrobot from following the desired path. In this article, we used two pairs of Helmholtz coils and two pairs of Maxwell coils in a two-dimensional electromagnetic actuation system. Generally, the two pairs of Helmholtz coils generate the torque for the rotation of the microrobot and the two pairs of Maxwell coils generate the propulsion force of the microrobot. Both pairs of Helmholtz and Maxwell coils have to work to simultaneously align and propel the microrobot in a desired direction. In this situation, however, the electromagnetic fields produced by the Helmholtz coils can interfere with those produced by the Maxwell coils. This interference is closely dependent on the position of the microrobot in the region of interest inside the electromagnetic coils system. This means that the alignment direction and propulsion force of the microrobot can be distorted according to the position of the microrobot. Therefore, we propose a compensation algorithm for the electromagnetic field interference using the position information of the microrobot to correct the magnetic field interferences. First, the interference of an electromagnetic field obeying the Biot–Savart law is analyzed by numerical analysis. Second, a position-based compensation algorithm for the locomotion of a microrobot is proposed. Various locomotion tests of a microrobot verified that the proposed compensation algorithm could reduce the normalized average tracking error from 5.25% to 1.92%.ARCHIVE Proceedings of the Institution of Mechanical Engineers Part C Journal of Mechanical Engineering Science 1989-1996 (vols 203-210) 10/2013; 227:1915~1926. · 0.59 Impact Factor
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ABSTRACT: Microactuators are an important tool for precise manipulation of components and materials in nanotechnologies. The problems of design and application of microactuators for micro- and nanopositioning, microassembly, and microrobotics are considered in this paper. The basic parameters and models of piezoelectric, magnetostriction, electromagnetic, electrostatic, electrothermal, and hybrid microactuators are described. A general information approach that implies the description of physical models used in order to analyze microactuator behavior and optimize their design is considered.Automatic Documentation and Mathematical Linguistics 12/2011; 45(6).
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ABSTRACT: The field of microrobotics dedicated to medical interventions although relatively new, is progressing at a very fast pace. Among the various accesses inside the body being investigated, the vascular network with close to 100,000 km of potential routes in each human and offering a large range of interventional opportunities has been of special interest in recent years. Although significant progresses and milestones have been achieved in this particular field of research, some important challenges remain to be solved before microrobotics in the human vasculature becomes a reality. Nonetheless, despite these challenges, some applications are already on the horizon. This paper aims at providing a quick overview of the present status of the field of microrobotics for interventions in the vascular network and to describe the main critical challenges that must be met in the short term to enable new or enhanced medical interventional procedures that may bring potential great outcomes for the patients.Journal of Micro-Bio Robotics. 02/2013; 8(1).
OctoMag: An Electromagnetic System
for 5-DOF Wireless Micromanipulation
B. E. Kratochvil, M. P. Kummer, J. J. Abbott, R. Borer, O. Ergeneman, and Bradley J. Nelson
Abstract—We demonstrate five-degree-of-freedom (5-DOF)
wireless magnetic control of a fully untethered microrobot
with a magnetic steering system we call OctoMag. Although
only occupying a single hemisphere, this system is capable of
isotropically applying forces on the order of 1–40 µN with
unrestricted control of the 2 orienting DOF. These capabilities
are enabled through the use of soft-magnetic-cores which
provide an increase of approximately 20× that of air cores
in magnetic-field strength, but comes at the cost of more
complicated interactions between coils. We propose a modeling
mechanism that assumes the field contributions of the individual
currents superimpose linearly when using cores with large
linear regions and negligible hysteresis. When designing the
system, the locations and quantity of electromagnets were
optimized with regards to the force generation in the worst-
case direction predicted by the model. The resultant system
is capable of both open and closed-loop operation over a
workspace of 4 cm3. OctoMag was primarily designed for the
control of intraocular microrobots for delicate retinal proce-
dures, but also has potential uses in other medical applications
or micromanipulation under an optical microscope.
One approach to the wireless control of microrobots is
through externally applied magnetic fields. These untethered
devices can navigate in bodily fluids to enable a number of
new minimally invasive therapeutic and diagnostic medical
procedures. We are particularly interested in intraocular mi-
crorobots, which have the potential to be used in ophthalmic
procedures such as drug delivery and remote sensing . One
particularly difficult procedure for vitreoretinal surgeons to
perform is retinal-vein cannulation—the injection of a clot-
busting enzyme into a tiny vein—which is at the limits of
human capabilities . A few groups have proposed robot-
assisted solutions for vitreoretinal surgery to attenuate the
surgeon’s hand tremor , . In these proposed robotic
solutions, the invasiveness of the procedure is not necessarily
reduced, and the delicate retina is still at risk from a tool that
is capable of inflicting irreparable damage.
In an effort to enable less invasive and safer retinal
surgery, as well as providing an increased level of dexterity
desired by clinicians, we embarked on the design of a
system for magnetic manipulation of a fully untethered
dexterous microrobotic device inside the eye. As opposed
to manual surgery and existing robots, which are fundamen-
tally position controlled, a magnetic device is fundamentally
force controlled, with localization required for closed-loop
This work is supported by the NCCR Co-Me of the Swiss National
Science Foundation. The authors are with the Institute of Robotics and
Intelligent Systems, ETH Zurich, 8092 Zurich, Switzerland. e-mail: bnel-
email@example.com. J. J. Abbott is now with the Department of Mechanical
Engineering, University of Utah, Salt Lake City, UT, 84112 USA.
position control. This makes a magnetic tool a safer device
for interacting with the retina: we can impose limits on
the system to make irreparable retinal damage impossible,
even in the event of patient movement or system failure.
Ophthalmic procedures are also unique among minimally
invasive medical procedures in that they provide a direct
line of sight for visual feedback, making closed-loop position
control of intraocular microrobots possible.
II. EXPERIMENTAL RESULTS
The prototype system is shown in Fig. 1, and consists
of eight stationary electromagnets with ferromagnetic cores.
Whereas magnetic manipulation has typically relied on or-
thogonal electromagnetic arrangements generating uniform
fields, which are simple in terms of modeling and control,
OctoMag’s unprecedented level of wireless control is due
to its utilization of complex nonuniform magnetic fields. In
its current configuration the OctoMag is capable of creating
field gradients up to 2 T/m and orienting fields up to
50 mT while steering the robot. A variety of devices is the
millimeter and submillimeter range can be controlled as end
effectors. We have thus far experimented with devices made
from microassembled CoNi pieces, stainless steel tubing, and
NdFeB permanent magnets.
Earnshaw’s theorem tells us that there can be no stable
static equilibria using ferromagnetism. That is, to maintain
a stable position of the microrobot, we must use feedback
control. Once we have implemented gravity compensation,
we empirically find that the drift of the microrobot in a
static field is quite slow. During open-loop control, a 500 µm
microrobot drifts with a velocity of roughly 50 µm/s at the
diameter electromagnets. The gap between two opposing electromagnets on
the lower set is 130 mm. The insets are the top and side-camera views, and
show a 2-mm-long microrobot of the type described in .
The OctoMag prototype contains eight 210-mm-long by 62-mm-
2010 IEEE International Conference on Robotics and Automation
Anchorage Convention District
May 3-8, 2010, Anchorage, Alaska, USA
978-1-4244-5040-4/10/$26.00 ©2010 IEEE1080
Fig. 2. Demonstration of rotation control. Both time-lapse image sequences
show a single 2-mm-long microrobot in the z = 0 plane (viewed from
above). The left image sequence demonstrates rotation of the microrobot in
place at an arbitrary location in space by relying on pure open-loop control.
The right image sequence demonstrates rotation of the microrobot about a
remote center at an arbitrary location using closed-loop control.
center of the workspace and 140 µm/s at the extremity of
the workspace. We find that the human operator can regulate
the position quite well using only visual feedback (Fig. 2),
although not with the level of precision as when using the
computer-vision tracker for closed-loop control (Fig. 3).
A chick choriallantoic membrane (CAM) has been demon-
strated to be a viable model tissue for surgical retinal research
and simulation . Figure 4 shows a permanent magnetic
device equipped with a needle tip being used to puncture a
blood vessel. This demonstrates that an untethered magnetic
agent is able to be manipulated with enough dexterity and
force to potentially deliver enzymes or other clot-busting
agents to the delicate structures of the eye.
Although OctoMag was designed for the control of in-
traocular microrobots for minimally invasive retinal therapy
and diagnosis, it additionally has great potential for use as a
wireless micromanipulation system under a light microscope.
 O. Ergeneman, G. Dogangil, M. P. Kummer, J. J. Abbott, M. K.
Nazeeruddin, and B. J. Nelson, “A magnetically controlled wireless
optical oxygen sensor for intraocular measurements,” IEEE Sensors J.,
vol. 8, no. 1, pp. 29–37, 2008.
 S. P. N. Singh and C. N. Riviere, “Physiological tremor amplitude
during retinal microsurgery,” in IEEE Northeast Bioengineering Conf.,
2002, pp. 171–172.
 B. Mitchell, J. Koo, I. Iorcachita, P. Kazanzides, A. Kapoor, J. Handa,
G. Hager, and R. Taylor, “Development and application of a new steady-
hand manipulator for retinal surgery,” in Proc. IEEE Int. Conf. Robotics
and Automation, 2007, pp. 623–629.
long microrobot aligned with the Z axis (vertical). The left composite image
demonstrates movement in a plane offset by -1.5 mmoff the X-Z plane
(viewed from the side). The right image sequence demonstrates movement
in a plane offset 1.5 mmoff the X-Y plane (viewed from above). The
microrobot was moved along the edges of a cube as displayed in the
isometric graph (b). ◦ indicate waypoints. + indicate tracker data.
Demonstration of automated position control. (a) show a 2-mm-
 W. Wei, R. E. Goldman, H. F. Fine, S. Chang, and N. Simaan, “Per-
formance evaluation for multi-arm manipulation of hollow suspended
organs,” IEEE Trans. Robotics, vol. 25, no. 1, pp. 147–157, 2009.
 K. B. Yesin, K. Vollmers, and B. J. Nelson, “Modeling and control of
untethered biomicrorobots in a fluidic environment using electromag-
netic fields,” Int. J. Robotics Research, vol. 25, no. 5–6, pp. 527–536,
 T. Leng, J. M. Miller, K. V. Bilbao, D. V. Palanker, P. Huie, and M. S.
Blumenkranz, “The chick chorioallantoic membrane as a model tissue
for surgical retinal research and simulation,” Retina, vol. 24, no. 3, pp.
(a) (b) (c)
Fig. 4.The OctoMag controlling a 2.5-mm-long NdFeB agent with a needle tip to puncture vasculature on a CAM.