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Manipulation with a Single Permanent Magnet for Capsule Endoscopy

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 prior 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.

Using Rotating Dipole Fields for Magnetic Capsule Endoscopy of the Small Bowel

This video shows simultaneous localization and propulsion of a magnetic capsule in bovine intestines. The Spherical-Actuator-Magnet Manipulator (SAMM) generates a rotating magnetic field that applies torque to the capsule, which has screw threads that enable the capsule to convert rotation to forward translation. Sensors in the capsule broadcast the field it sees, which enables us to localize the capsule.

This video shows our first demonstration of simultaneous localization and propulsion of a magnetic capsule. The Spherical-Actuator-Magnet Manipulator (SAMM) generates a rotating magnetic field that applies torque to the capsule, which has screw threads that enable the capsule to convert rotation to forward translation. Sensors in the capsule broadcast the field it sees, which enables us to localize the capsule. More detail can be found in the paper First Demonstration of Simultaneous Localization and Propulsion of a Magnetic Capsule in a Lumen using a Single Rotating Magnet. This work was awarded the Best Paper Award in Medical Robotics at ICRA 2017.

This video shows our ability to perform magnetic localization of a capsule. The Spherical-Actuator-Magnet Manipulator (SAMM) generates a rotating magnetic dipole field, and sensors inside the capsule broadcast the field that they measure, which enables us to localize the capsule. The SAMM then engages with the capsule and drives it open-loop for a short duration of time (without updating the estimate of the capsule's location). The SAMM then disengages and relocalizes the capsule. This process is repeated. The cameras are providing ground-truth, but are not being used in the magnetic control system. More detail can be found in the paper Six-degree-of-freedom Localization of an Untethered Magnetic Capsule Using a Single Rotating Magnetic Dipole.

This video shows a prototype magnetic capsule endoscope being driven through a fresh cow intestine (our first attempt). The capsule's position in the intestine is being localized using cameras.

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.

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 Fields with Permanent Magnets

The Spherical-Actuator-Magnet Manipulator (SAMM) is a permanent-magnet robot end-effector. It comprises a spherical permanent magnet and three mutually orthogonal onmiwheels that enable rotation of the magnet about arbitrary axes of rotation, without singularities or workspace limitations. Hall-effect sensors on the SAMM enable estimation of the orientation of magnetic dipole. More details can be found in the paper The Spherical-Actuator-Magnet Manipulator: A Permanent-Magnet Robotic End-Effector.

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.


Selected Publications

K. M. Popek, T. Hermans, and J. J. Abbott, "First Demonstration of Simultaneous Localization and Propulsion of a Magnetic Capsule in a Lumen using a Single Rotating Magnet", IEEE Int. Conf. Robotics and Automation, pp. 1154-1160, 2017. Best Paper Award in Medical Robotics.
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S. E. Wright, A. W. Mahoney, K. M. Popek, and J. J. Abbott, "The Spherical-Actuator-Magnet Manipulator: A Permanent-Magnet Robotic End-Effector", IEEE Trans. Robotics, 33(5):1013-1024, 2017.
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K. M. Popek, T. Schmid, and J. J. Abbott, "Six-degree-of-freedom Localization of an Untethered Magnetic Capsule Using a Single Rotating Magnetic Dipole", IEEE Robotics and Automation Letters, 2(1):305-312, 2017.
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A. W. Mahoney and J. J. Abbott, "Five-degree-of-freedom Manipulation of an Untethered Magnetic Device in Fluid using a Single Permanent Magnet with Application in Stomach Capsule Endoscopy," Int. J. Robotics Research, 35(1-3):129-147, 2016.
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A. W. Mahoney and J. J. Abbott, "Generating Rotating Magnetic Fields with a Single Permanent Magnet for Propulsion of Untethered Magnetic Devices in a Lumen," IEEE Trans. Robotics, 30(2):411-420, 2014.
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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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A. W. Mahoney and J. J. Abbott, "5-DOF Manipulation of a Magnetic Capsule in Fluid using a Single Permanent Magnet: Proof-of-concept for Stomach Endoscopy," Hamlyn Symp. Medical Robotics, pp. 114-115, 2013. Best Poster Award. The definitive version of this work is in the journal paper "Five-degree-of-freedom Manipulation of an Untethered Magnetic Device in Fluid using a Single Permanent Magnet with Application in Stomach Capsule Endoscopy."

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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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 February 14, 2018, at 01:36 PM