Magnetic continuum robots (MCR) have shown great potential in minimally invasive interventions because they can be actively and remotely navigated through complex in vivo environments. However, the deformation capability of current MCRs is limited by fixed magnetization congurations, preventing them from accessing hard-to-reach areas. This is due to the fact that under a global magnetic field, fixed magnetization conguration causes the magnets on the MCRs exposed to coupled magnetic forces and torques, resulting in a lack of controllable degrees of freedom. Here, we introduce a reprogrammable magnetic continuum robot (RMCR) enabled by magnetic reprogramming modules (MRM). Actuated by shape memory alloys, the magnetic moment direction of MRMs can be selectively reprogrammed in real-time and in-situ. Magnetic reprogramming capabilities enable the RMCR to achieve complex shape transformations. Results show that the range of motion in the tip direction of the RMCR increases by 193% compared with regular MCR. Besides, MRMs on the RMCR can achieve active attraction and separation under simple magnetic fields. The reprogramming process of the RMCR is theoretically investigated. A design methodology for MRMs is then proposed and the fabrication process of RMCR is described in detail. Furthermore, a kinematic model of the RMCR is established, simulated, and experimentally validated.

In this work, we study the optimal parameter design and microrobotic navigation control of the parallel-mobile-coil system (PMCS) that consists of three mobile electromagnetic coils. With motion driven by a parallel mechanism, the three coils can move in 3D large space and keep as close as possible to the controlled microrobot for magnetic actuation. Although promising for microrobotic applications, how to design such a type of system for a specific workspace requirement is untackled. Regarding this issue, we propose a computational design method, by which one can calculate the structural parameters of a PMCS starting from a required cylindrical workspace. With the derived performance metrics for motion actuation and magnetic actuation of the PMCS, the system actuation performance (composed of motion and magnetic actuation) is optimized. Utilizing the design method, we optimally construct a prototype PMCS for microrobotic navigation. We then conduct experiments to validate the demanding field/force generation capability of the PMCS and demonstrate the navigation control of different types of magnetic microrobots. In particular, we design closed-loop motion controllers for both torque and force-driven microrobots, using which automated large-workspace and high-accuracy trajectory tracking is realized. Note to Practitioners—This work is motivated by the recent wide interest in magnetic microrobots. Driven by external magnetic fields, magnetic microrobots can navigate in a wireless manner for targeted delivery/therapy. To promote microrobot applications to the human body, a magnetic actuation system with large workspace is desirable. However, due to the fast decay of magnetic field, the commonly used stationary coil-based magnetic actuation systems have the workspace scalability problem. Thus, several mobile-coil-based systems have been designed. In this work, we propose an optimal design method for the PMCS, using which one can design a PMCS starting from a cylindrical workspace with performance being optimized. We construct a PMCS prototype with a workspace of$\Phi 230 \times 100$mm3, and we then study the automated microrobotic navigation control methods for the PMCS. Controllers are designed for different types of magnetic microrobots, and experiments show that, using the controllers, the PMCS can perform automated large-workspace microrobotic navigation control with high accuracy.

Magnetic field is a favorable power source for actuation and control of micro-/nanorobots. To overcome the fast decay of magnetic field for large-workspace microrobotic actuation, mobile field source-based systems have been proposed. In this work, we report a new mobile-coil system, i.e., QuadMag. It consists of four electromagnetic coils, whose motion is actuated by a parallel mechanism. Compared to previous systems with three mobile coils, e.g., DeltaMag, the additional coil in the QuadMag increases the degree-of-freedom (DoF) for magnetic control. However, to control QuadMag, new control methods should be developed for the over-constrained parallel mechanism and for the field/force of the four coils. We derive the Jacobian matrix for the differential motion of the parallel mechanism and then formulate the field, force and simultaneous field and force control methods for magnetic actuation. Comparative experiments validate the enhanced actuation efficiency when controlling torque-driven helical microrobots. Moreover, the magnetic actuation dexterity is also enhanced by the additional coil. We conduct simulated navigation experiments and prove the actuation capability of QuadMag for 3D force-driven microrobot navigation with controlled robot orientation.

Mechanical rubbing of blood clot using miniature magnetic helical robots is a potential way for thrombolysis. In this paper, we report a new strategy for this issue based on mobile coils. Previously, we proposed the concept of magnetic actuation with parallel mobile coils, in which multiple coils can move in 3D space. Enabled by mobility of the coils, additional degree-of-freedom (DOF) could be utilized for actuation performance optimization. Besides the primary helical propulsion by rotating magnetic fields, our strategy aims to optimize the coil motion to make the magnetic force contributes the most to the helical robot forward motion. For this goal, modeling of the magnetic field and force of multiple mobile coils are presented, based on which an optimization algorithm is formulated to output the best coil motion. For validation, an enhanced mobile coil system having a workspace of Φ500 mm ×150 mm is constructed based on the parallel mobile coil concept. Simulations show the effectiveness of the proposed strategy, whose effective workspace for a specific task can also be obtained. After implementing the proposed strategy, preliminary experiments using clot analog demonstrate that the removal speed is accelerated over 50% compared to that without coil motion optimization.

Large workspace localization of magnetic robots is important for medical applications. This paper presents a novel localization strategy to achieve simultaneous localization and actuation of magnetic robots using hall-effect sensors. We integrate 25 sensors into a sensing probe and mount it on to the mobile-coil system, which realizes accurate sensing and actuation of magnetic devices within a cylindrical workspace of ϕ500 mm×150 mm. Simulation results show the average localization error using the proposed method is 1.7 mm. A verification experiment is conducted to prove the design advantages; Another two experiments are conducted to demonstrate the simultaneous actuation and localization of a torque-driven robot and a force-driven floating robot respectively. For the force-driven floating robot, the average variation between the localization results and the desired trajectory is less than 2 mm.