Strong magnetic actuation system with enhanced field articulation through stacks of individually addressed coils

Miniaturization of medical tools promises to revolutionize surgery by reducing tissue trauma and accelerating recovery. Magnetic untethered devices, with their ability to access hard-to-reach areas without physical connections, emerge as potential candidates for such miniaturization. Despite the benefits, these miniature devices face challenges regarding force and torque outputs, restricting their ability to perform tasks requiring mechanical interactions such as tissue penetration and manipulation. To overcome magnetic actuation system-based force and torque limitations, this study proposes Variable Outer Radius Individually Addressable Coil Stacks (VORIACS), a novel magnetic actuation system optimized for high force output generation to magnetic devices within its workspace. The VORIACS marks significant improvements and breakthroughs in magnetic actuation within decimeter-scale workspace. The VORIACS is comprised of 12 coils that are optimized for 2D magnetic field generation under maximized power consumption of up to 12 kW. We implement six two-channel motor controllers, powered by six separate power supplies. Each of the twelve coils in the system is operated on its own motor-controller channel. This arrangement allows the system to exceed the magnetic forces and torques possible for single-coil versions of the same geometry. This study elaborates on optimizing, manufacturing, integrating, and demonstrating this system. Comparative analysis reveals that while a suboptimal, single-coil version of this system generates 0.31 N force (710 mT/m magnetic gradient magnitude), the VORIACS produces 1.673 N force (3834 mT/m magnetic gradient magnitude) on the same magnetic object placed 5 cm away from the coils. Moreover, the strong penetration force generated by VORIACS enables needle penetration to a mock gel that has the rigidity of liver tissue. In addition, we demonstrate the advantage of stacked coils with variable radii for magnetic field manipulability while maintaining the optimized force delivery property of the system, which improves control and could facilitate multi-tool manipulation. By enabling a fivefold increase in magnetic pulling force compared to its single-coil counterpart, VORICAS raises the potential penetration capabilities of untethered magnetic robotics in surgical procedures.

Control of Magnetic Surgical Robots With Model-Based Simulators and Reinforcement Learning

Magnetically manipulated medical robots are a promising alternative to current robotic platforms, allowing for miniaturization and tetherless actuation. Controlling such systems autonomously may enable safe, accurate operation. However, classical control methods require rigorous models of magnetic fields, robot dynamics, and robot environments, which can be difficult to generate. Model-free reinforcement learning (RL) offers an alternative that can bypass these requirements. We apply RL to a robotic magnetic needle manipulation system. Reinforcement learning algorithms often require long runtimes, making them impractical for many surgical robotics applications, most of which require careful, constant monitoring. Our approach first constructs a model-based simulation (MBS) on guided real-world exploration, learning the dynamics of the environment. After intensive MBS environment training, we transfer the learned behavior from the MBS environment to the real-world. Our MBS method applies RL roughly 200 times faster than doing so in the real world, and achieves a 6 mm root-mean-square (RMS) error for a square reference trajectory. In comparison, pure simulation-based approaches fail to transfer, producing a 31 mm RMS error. These results demonstrate that MBS environments are a good solution for domains where running model-free RL is impractical, especially if an accurate simulation is not available.