The paper addresses the 2D observer-based control of a magnetic microrobot navigating in a cylindrical blood vessel along a reference trajectory. In particular, this robot faces the nonlinear drag force induced by the pulsatile blood flow, which can hardly be measured. Consequently, a mean value theorem (MVT) based observer to estimate the blood velocity from the sole measurement of the robot position is proposed. Also, the stability of the observer-based backstepping controller is proved. The resulting estimation and tracking are then illustrated through simulations, as well as robustness to parametric uncertainty, measurement noise, and dynamical errors when the pulsatile blood flow is incorrectly modeled.

Multi-microagent systems are appealing to perform targeted therapy, biosensing and diagnosis. However on most magnetic platforms, the magnetic field is stationary so all the robots experience the same control input, resulting in an underactuated system. However, to date, the controllability of underactuated microsystems had hardly been addressed. This paper thus investigates the system local controllability. This result highlights the necessity for the agents to operate in close vicinity to achieve trajectory tracking along an admissible reference trajectory whose choice is discussed. We then propose a backstepping controller to locally stabilize the nonlinear system. Simulations illustrate this approach efficiency and limitations for different designs of the microrobotic system.

Abstract-We propose an observer-based controller for a magnetic microrobot immersed in the human vasculature. The drag force depends on the pulsatile blood velocity and specially acts on the microrobot dynamics. In the design of advanced control laws, the blood velocity is usually assumed to be known or set to a constant mean value to achieve the control objectives, whereas the sole robot position is measured. We prove the stability of the proposed observer-based controller combining a backstepping controller with a mean value theorem (MVT) based observer. The resulting estimation of the blood velocity is then illustrated and compared to high gain observer results through simulations.