Multimode Control of a Parallel-Mobile-Coil System for Adaptable Large-Workspace Microrobotic Actuation

Recent studies on magnetic microrobotics for biomedical applications have resulted in varieties of magnetic actuation systems. However, the simultaneous actuation and tracking of magnetic microrobots in large workspace (e.g., the human-body size) remains challenging due to the fast decay of magnetic fields and the contradiction between resolution and field of view of a feedback instrument. Our previous work reported the concept of the parallel-mobile-coil system (PMCS), which comprises three electromagnetic coils that can move in large 3-D space for microrobotic actuation. Here, to make the PMCS have adaptability to different actuation scenarios or microrobot types, we propose three different control modes by utilizing the mobility of the coils. The torque control, force-assisted torque control, and force control modes are designed for pure torque actuation with energy conservation, torque actuation with force assistance, and pure force actuation, respectively. Comparative simulations and experiments validate the effectiveness of the three control modes. Moreover, to endow the system with <italic>in-vivo</italic> feedback capability, we implement Hall-effect sensors and demonstrate the 3-D large-workspace actuation based on magnetic localization.