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Manipulation with a Single Permanent Magnet

Externally applied magnetic fields will enable untethered devices to navigate the body for minimally invasive surgical and diagnostic procedures. We are particularly interested in active capsule endoscopy. Much of the research done on helical swimmers and screws has utilized electromagnetic coil arrangements for control, but these are difficult to scale up to the size of a human body. We believe that it is possible to control such device using a single permanent magnet moved and rotated dynamically through space.

5-DOF Control for Capsule Endoscopy of the Stomach

This video shows an example of mockup magnetic capsule endoscope in a water-filled tank being manipulated by a single permanent magnet that is positioned in space with a robotic manipulator. In this demonstration, the algorithm performs a U-shaped position trajectory (down, right, up) while maintaining the capsule's heading. The capsule's 3-D position (but not orientation) is being detected by two cameras; in a clinical setting this 3-D localization must be performed by other means.

This video shows an example of mockup magnetic capsule endoscope in a water-filled tank being manipulated by a single permanent magnet that is positioned in space with a robotic manipulator. In this demonstration, the algorithm attempts to rotate the capsule by 90 degrees while maintaining its position in space. The capsule's 3-D position (but not orientation) is being detected by two cameras; in a clinical setting this 3-D localization must be performed by other means.

Generating Rotating Fields for Capsule Endoscopy of the Small Bowel

There is a class of untethered microrobots that use helical propellers to swim using a method inspired by the propulsion of bacteria. When a piece of magnetic material is attached to the helical propeller, then magnetic fields can be used to rotate the microrobot for propulsion, as well as to steer the microrobot. Tiny magnetic screws can drill through soft tissue using a related method of propulsion. Magnetic spheres can roll on surfaces.

This video shows a prototype magnetic capsule endoscope being driven through a fresh cow intestine.

This video shows a spherical device with an embedded permanent magnet being driven by a rotating permanent magnet on a robotic manipulator. Two different trajectories in the video demonstrate that, using our developed algorithms, it is possible to create a consistent rotating magnetic field in some location in space using a rotating permanent magnet in any position, provided that the axis of rotation is correct. This is a very unintuitive and powerful result. More detail can be found in the paper Control of Untethered Magnetically Actuated Tools using a Rotating Permanent Magnet in any Position.

This video shows a threaded capsule-endoscope device with an embedded permanent magnet being driven by a rotating permanent magnet on a robotic manipulator. Three different trajectories in the video demonstrate that, using our developed algorithms, it is possible to create a consistent rotating magnetic field in some location in space using a rotating permanent magnet in any position, provided that the axis of rotation is correct. It is easier to propel the capsule from positions where the attractive magnetic force is in the desired direction of motion. This is a very unintuitive and powerful result. More detail can be found in the paper Control of Untethered Magnetically Actuated Tools using a Rotating Permanent Magnet in any Position.

When this video begins, a small cylindrical magnet is at an equilibrium position where the attractive magnetic force counterbalances gravity. By rotating the large magnet using a specific dynamic trajectory, the attractive magnetic force is pointed upward, resulting in levitation of the small magnet. More detail can be found in the paper Managing Magnetic Force Applied to a Magnetic Device by a Rotating Dipole Field.

This video shows a helical magnetic microswimmer being driven using the nonuniform field of a single rotating permanent magnet. To date, magnetic helical microrobots have always been controlled using nested sets of electromagnetic coils, with the microrobot located at the "sweet spot" in the well-conditioned center of the workspace: a method that works well in laboratory settings, but doesn't scale well for clinical use. This new rotating-permanent-magnetic manipulator has more potential for control of medical microrobots. More details can be found in the paper Wireless Control of Magnetic Helical Microrobots using a Rotating-Permanent-Magnet Manipulator.


Modeling the Field of Permanent Magnets

The manipulation methods that we have developed utilize a point-dipole model of the field generated by the permanent magnet. Only spherical magnets have a field that truly looks like a point dipole, and for other magnet geometries the model is just an approximation. We found the aspect ratios for a variety of common geometries (axially magnetized cylinders, diametrically magnetized cylinders, washers, rectangular-cross-section bars) that result in a minimum error when using the point-dipole model. More details can be found in the paper Optimal Permanent-Magnet Geometries for Dipole Field Approximation.


Localization and Feedback Control of Capsules

Coming Soon.


Selected Publications

A. W. Mahoney, S. E. Wright, and J. J. Abbott, "Managing the Attractive Magnetic Force between an Untethered Magnetically Actuated Tool and a Rotating Permanent Magnet," IEEE Int. Conf. Robotics and Automation, pp. 5346-5351, 2013.
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K. M. Popek, A. W. Mahoney, and J. J. Abbott, "Localization Method for a Magnetic Capsule Endoscope Propelled by a Rotating Magnetic Dipole Field," IEEE Int. Conf. Robotics and Automation, pp. 5328-5333, 2013.
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A. J. Petruska and J. J. Abbott, "Optimal Permanent-Magnet Geometries for Dipole Field Approximation," IEEE Trans. Magnetics, 49(2):811-819, 2013.
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K. M. Miller, A. W. Mahoney, T. Schmid, and J. J. Abbott, "Proprioceptive Magnetic-Field Sensing for Closed-loop Control of Magnetic Capsule Endoscopes," IEEE/RSJ Int. Conf. Intelligent Robots and Systems, pp. 1994-1999, 2012.
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A. W. Mahoney and J. J. Abbott, "Control of Untethered Magnetically Actuated Tools with Localization Uncertainty using a Rotating Permanent Magnet," IEEE Int. Conf. Biomedical Robotics and Biomechatronics, pp. 1632-1637, 2012.
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A. W. Mahoney, D. L. Cowan, K. M. Miller, and J. J. Abbott, "Control of Untethered Magnetically Actuated Tools using a Rotating Permanent Magnet in any Position," IEEE Int. Conf. Robotics and Automation, pp. 3375-3380, 2012.
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A. W. Mahoney and J. J. Abbott, "Managing Magnetic Force Applied to a Magnetic Device by a Rotating Dipole Field," Applied Physics Letters, 99(134103):1-3, 2011.
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T. W. R. Fountain, P. V. Kailat, and J. J. Abbott, "Wireless Control of Magnetic Helical Microrobots using a Rotating-Permanent-Magnet Manipulator," IEEE Int. Conf. Robotics and Automation, pp. 576-581, 2010. Finalist, Best Medical Robotics Paper Award.
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Sponsors

This material is based in part upon work supported by the National Science Foundation under Grant No. 0952718. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

Page last modified on June 20, 2013, at 09:12 AM