Control of Microrobots Using Model Predictive Control and Gaussian Processes for Disturbance Estimation

This paper presents a control framework for magnetically actuated micron-scale robots ($\mu$bots) designed to mitigate disturbances and improve trajectory tracking. To address the challenges posed by unmodeled dynamics and environmental variability, we combine data-driven modeling with model-based control to accurately track desired trajectories using a relatively small amount of data. The system is represented with a simple linear model, and Gaussian Processes (GP) are employed to capture and estimate disturbances. This disturbance-enhanced model is then integrated into a Model Predictive Controller (MPC). Our approach demonstrates promising performance in both simulation and experimental setups, showcasing its potential for precise and reliable microrobot control in complex environments.

Learning for Control of Rolling ubots

Micron-scale robots (ubots) have recently shown great promise for emerging medical applications, and accurate control of ubots is a critical next step to deploying them in real systems. In this work, we develop the idea of a nonlinear mismatch controller to compensate for the mismatch between the disturbed unicycle model of a rolling ubot and trajectory data collected during an experiment. We exploit the differential flatness property of the rolling ubot model to generate a mapping from the desired state trajectory to nominal control actions. Due to model mismatch and parameter estimation error, the nominal control actions will not exactly reproduce the desired state trajectory. We employ a Gaussian Process (GP) to learn the model mismatch as a function of the desired control actions, and correct the nominal control actions using a least-squares optimization. We demonstrate the performance of our online learning algorithm in simulation, where we show that the model mismatch makes some desired states unreachable. Finally, we validate our approach in an experiment and show that the error metrics are reduced by up to 40%.

Closed-loop Control of Catalytic Janus Microrobots

We report a closed-loop control system for paramagnetic catalytically self-propelled Janus microrobots. We achieve this control by employing electromagnetic coils that direct the magnetic field in a desired orientation to steer the microrobots. The microrobots move due to the catalytic decomposition of hydrogen peroxide, during which they align themselves to the magnetic torques applied to them. Because the angle between their direction of motion and their magnetic orientation is a priori unknown, an algorithm is used to determine this angular offset and adjust the magnetic field appropriately. The microrobots are located using real-time particle tracking that integrates with a video camera. A target location or desired trajectory can be drawn by the user for the microrobots to follow.