The ARMM System: An Optimized Mobile Electromagnetic Coil for Non-Linear Actuation of Flexible Surgical Instruments

Automation of flexible surgical instruments requires the development of robotic technologies capable of small-scale power transmission. Magnetic actuation has successfully been used for that purpose. Nevertheless, current systems for magnetic actuation suffer from small workspaces or poor bandwidth of magnetic field control. In this work, we design, develop, and test a novel magnetic actuation system called Advanced Robotics for Magnetic Manipulation (ARMM). The ARMM system employs a 6 DoF mobile electromagnetic coil capable of generating prescribed magnetic fields and gradients. The mobile coil approach allows for easy scaling of the actuation workspace, which depends on the range of robotic arm, and in our case spans up to 1.3 m. Due to limited end-effector payload of the robotic arm used in the ARMM system, the mobile coil has been designed using an optimization routine. For a given mass and heat dissipation constraints, this routine provides the coil geometry that maximizes the average magnetic field generated in the target region. Since the Vacoflux core of the fabricated coil saturates within operational conditions, we propose an actuation strategy employing an online-updated iterative map technique. Using this map, the ARMM system allows for precise generation of prescribed magnetic fields and gradients at the point of interest, while taking into account the effects of the non-linearities due to core saturation. The strategy is validated experimentally, showing the average error of 2.34% for magnetic field and 7.20% for the magnetic field gradient.