Magnetic actuation of a cylindrical microrobot using time-delay-estimation closed-loop control: modeling and experiments

Accurate control systems are critical for safe and practical utilization of microrobots for in vivo operations. There exist uncertainties from the microrobot dynamics and nonlinearities from the magnetic driving force in the electromagnetic in vivo manipulation of microrobots, especially in low Reynolds number fluid flow. We describe the modeling and implementation of a closed-loop control system for a magnetically actuated microrobot based on time-delay estimation (TDE). The microrobot consisted of a cylindrical magnet, 0.5 mm in diameter and 1 mm in length, and the controller used optical sensing for position feedback. In addition, we describe an analytical model to determine the magnetic field components and the field gradients of a custom set of coils used to actuate the microrobot. Simulations were carried out to investigate the properties of the TDE control system, and it was subsequently tested experimentally, demonstrating that it provides robust control of the microrobot trajectory and does not exhibit chattering to follow step inputs.