Doctor of Philosophy

dissertationClosed-loop control of wireless capsule endoscopes is an active area of research because it would drastically improve screening of the gastrointestinal tract. Traditional endoscopic procedures are unable to view the entire gastrointestinal tract and current commercial wireless capsule endoscopes are limited in their effectiveness due to their passive nature. This dissertation advances the field of active capsule endoscopy by developing methods to localize the full six-degree-of-freedom (6-DOF) pose of a screw-type magnetic capsule while it is being propelled through a lumen (such as the small intestines) using an external rotating magnetic dipole. The same external magnetic dipole is utilized for both propulsion and localization. Hardware was designed and constructed to enable testing of the magnetic localization and propulsion methods, including a robotic end-effector used as the external actuator magnet, and a prototype capsule embedded with Hall-effect sensors. Due to the use of a rotating magnetic field for propulsion, at any given time, the capsule can be in one of three regimes: synchronously rotating with the applied field, in "step-out" where it is free to move but the external field is rotating too quickly for the capsule to remain synchronously rotating, or completely stationary. We show that it is only necessary to distinguish whether or not the capsule is synchronously rotating (i.e., a single localization method can be used for a capsule in either the step-out or stationary regimes). Two magnetic localization methods are developed. The first uses nonlinear least squares to estimate the capsule's pose when it has no (or approximately no) net motion (e.g., to find the initial capsule pose or when it is stuck in an intestinal fold). The second method estimates the 6-DOF capsule pose as it synchronously rotates with the applied magnetic field using a square-root variant of the Unscented Kalman filter. A simple process model is adopted that restricts the capsule's movement to translation along and rotation about its principle axis. The capsule is actively propelled forward or backward, but it is not actively steered, rather, steering is provided by the lumen. The propulsion parameters that transform magnetic force and torque to the capsule's spatial velocity and angular velocity are estimated with an additional square-root Unscented Kalman filter to enable the capsule to navigate heterogeneous environments such as the small intestines. An optimized localization-propulsion system is described using the two localization algorithms and prior work in screw-type magnetic capsule propulsion with a single rotating dipole field. The capsule's regime is determined and the corresponding localization method is employed. Based on the capsule's estimated pose and the current estimates of its propulsion parameters, the actuator magnet's pose relative to the capsule is optimized to maximize the capsule's forward propulsion. Using this system, our prototype magnetic capsule successfully completed U-shaped and S-shaped trajectories in fresh bovine intestines with an average forward velocity of 5.5mm/s and 3.5 mm/s, respectively. At this rate it would take approximately 18-30 minutes to traverse the 6 meters of a typical human small intestine

Capsule endoscopy of the future: What's on the horizon?

Capsule endoscopes have evolved from passively moving diagnostic devices to actively moving systems with potential therapeutic capability. In this review, we will discuss the state of the art, define the current shortcomings of capsule endoscopy, and address research areas that aim to overcome said shortcomings. Developments in capsule mobility schemes are emphasized in this text, with magnetic actuation being the most promising endeavor. Research groups are working to integrate sensor data and fuse it with robotic control to outperform today's standard invasive procedures, but in a less intrusive manner. With recent advances in areas such as mobility, drug delivery, and therapeutics, we foresee a translation of interventional capsule technology from the bench-top to the clinical setting within the next 10 years

Doctor of Philosophy

dissertationThis dissertation presents results documenting advancements on the control of untethered magnetic devices, such as magnetic \microrobots" and magnetically actuated capsuleendoscopes, motivated by problems in minimally invasive medicine. This dissertationfocuses on applying rotating magnetic elds for magnetic manipulation. The contributions include advancements in the way that helical microswimmers (devices that mimicthe propulsion of bacterial agella) are controlled in the presence of gravitational forces, advancements in ways that groups of untethered magnetic devices can be dierentiated and semi-independently controlled, advancements in the way that untethered magnetic device can be controlled with a single rotating permanent magnet, and an improved understanding in the nature of the magnetic force applied to an untethered device by a rotating magnet

Doctor of Philosophy

dissertationThis dissertation explores the design and use of an electromagnetic manipulation system that has been optimized for the dipole-eld model. This system can be used for noncontact manipulation of adjacent magnetic tools and combines the eld strength control of current electromagnetic systems with the analytical modeling of permanent-magnet systems. To design such a system, it is rst necessary to characterize how the shape of the eld source aects the shape of the magnetic eld. The magnetic eld generated by permanent magnets and electromagnets can be modeled, far from the source, using a multipole expansion. The error associated with the multipole expansion is quantied, and it is shown that, as long as the point of interest is 1.5 radii of the smallest sphere that can fully contain the magnetic source, the full expansion will have less than 1% error. If only the dipole term, the rst term in the expansion, is used, then the error is minimized for cylindrical shapes with a diameter-to-length ratio of 4=3 and for rectangular-bars with a cube. Applying the multipole expansion to electromagnets, an omnidirectional electromagnet, comprising three orthogonal solenoids and a spherical core, is designed that has minimal dipole-eld error and equal strength in all directions. Although this magnet can be constructed with any size core, the optimal design contains a spherical core with a diameter that is 60% of the outer dimension of the magnet. The resulting magnet's ability to dextrously control the eld at a point is demonstrated by rotating an endoscopic-pill mockup to drive it though a lumen and roll a permanent-magnet ball though several trajectories. Dipole elds also apply forces on adjacent magnetized objects. The ability to control these forces is demonstrated by performing position control on an orientation-constrained magnetic oat and nally by steering a permanent magnet, which is aligned with the applied dipole eld, around a rose curve

Enhanced real-time pose estimation for closed-loop robotic manipulation of magnetically actuated capsule endoscopes

Pose estimation methods for robotically guided magnetic actuation of capsule endoscopes have recently enabled trajectory following and automation of repetitive endoscopic maneuvers. However, these methods face significant challenges in their path to clinical adoption including the presence of regions of magnetic field singularity, where the accuracy of the system degrades, and the need for accurate initialization of the capsule's pose. In particular, the singularity problem exists for any pose estimation method that utilizes a single source of magnetic field if the method does not rely on the motion of the magnet to obtain multiple measurements from different vantage points. We analyze the workspace of such pose estimation methods with the use of the point-dipole magnetic field model and show that singular regions exist in areas where the capsule is nominally located during magnetic actuation. Since the dipole model can approximate most magnetic field sources, the problem discussed herein pertains to a wider set of pose estimation techniques. We then propose a novel hybrid approach employing static and time-varying magnetic field sources and show that this system has no regions of singularity. The proposed system was experimentally validated for accuracy, workspace size, update rate and performance in regions of magnetic singularity. The system performed as well or better than prior pose estimation methods without requiring accurate initialization and was robust to magnetic singularity. Experimental demonstration of closed-loop control of a tethered magnetic device utilizing the developed pose estimation technique is provided to ascertain its suitability for robotically guided capsule endoscopy. Hence, advances in closed-loop control and intelligent automation of magnetically actuated capsule endoscopes can be further pursued toward clinical realization by employing this pose estimation system

Study on Magnetic Control Systems of Micro-Robots

Magnetic control systems of micro-robots have recently blossomed as one of the most thrilling areas in the field of medical treatment. For the sake of learning how to apply relevant technologies in medical services, we systematically review pioneering works published in the past and divide magnetic control systems into three categories: stationary electromagnet control systems, permanent magnet control systems and mobile electromagnet control systems. Based on this, we ulteriorly analyze and illustrate their respective strengths and weaknesses. Furthermore, aiming at surmounting the instability of magnetic control system, we utilize SolidWorks2020 software to partially modify the SAMM system to make its final overall thickness attain 111 mm, which is capable to control and observe the motion of the micro-robot under the microscope system in an even better fashion. Ultimately, we emphasize the challenges and open problems that urgently need to be settled, and summarize the direction of development in this field, which plays a momentous role in the wide and safe application of magnetic control systems of micro-robots in clinic

Geometric analysis of the singularities of a magnetic manipulation system with several mobile coils.

International audienceIt has been demonstrated that magnetic fields are relevant for manipulating an untethered magnet, either using fixed coils or mobile permanent magnets. This paper shows however, that any magnetic manipulation method is prone to singular configurations and that the simple numerical analysis of the rank of the "manipulation matrix" is not enough to detect them. Alternatively, we propose a geometrical analysis to interpret and detect the singularities as well as to decide on the acceptability of a reference trajectory. Then, we present results obtained by simulating a planar manipulation system including a multiple mobile coils and a Helmholtz like set-up