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This paper introduces a vision-guided control framework for autonomous navigation of a magnetic millirobot within an *in vitro* heart phantom, addressing the challenge of pulsatile cardiac flow disturbances. They employ a UNet for robot localization, A* for path planning, and a sliding mode controller with disturbance observer (SMC-DOB) for robust electromagnetic actuation. Experimental results demonstrate that the SMC-DOB controller significantly outperforms PID and MPC baselines, maintaining sub-millimeter accuracy in static fluid and robust tracking under varying pulsatile flow conditions, even with low viscosity.
A clever disturbance observer makes millirobot navigation in simulated heart flows robust enough for real-world drug delivery applications.
Untethered magnetic millirobots offer significant potential for minimally invasive cardiac therapies; however, achieving reliable autonomous control in pulsatile cardiac flow remains challenging. This work presents a vision-guided control framework enabling precise autonomous navigation of a magnetic millirobot in an in vitro heart phantom under physiologically relevant flow conditions. The system integrates UNet-based localization, A* path planning, and a sliding mode controller with a disturbance observer (SMC-DOB) designed for multi-coil electromagnetic actuation. Although drag forces are estimated using steady-state CFD simulations, the controller compensates for transient pulsatile disturbances during closed-loop operation. In static fluid, the SMC-DOB achieved sub-millimeter accuracy (root-mean-square error, RMSE = 0.49 mm), outperforming PID and MPC baselines. Under moderate pulsatile flow (7 cm/s peak, 20 cP), it reduced RMSE by 37% and peak error by 2.4$\times$ compared to PID. It further maintained RMSE below 2 mm (0.27 body lengths) under elevated pulsatile flow (10 cm/s peak, 20 cP) and under low-viscosity conditions (4.3 cP, 7 cm/s peak), where baseline controllers exhibited unstable or failed tracking. These results demonstrate robust closed-loop magnetic control under time-varying cardiac flow disturbances and support the feasibility of autonomous millirobot navigation for targeted drug delivery.
