Nonlinear modeling and robust controller-observer for a magnetic microrobot in a fluidic environment using MRI gradients

International audienceThis paper reports the use of a MRI device to pull a magnetic microrobot inside a vessel and control its trajectory. The bead subjected to magnetic and hydrodynamic forces is first modeled as a nonlinear control system. Then, a backstepping approach is discussed in order to synthesize a feedback law ensuring the stability along the controlled trajectory. We show that this control law, combined with a high gain observer, provides good tracking performances and robustness to measurement noise as well as to some matched uncertainties

A Robust controller for micro-sized agents: The prescribed performance approach

Applications such as micromanipulation and minimally invasive surgery can be performed using micro-sized agents. For instance, drug-loaded magnetic micro-/nano- particles can enable targeted drug delivery. Their precise manipulation can be assured using a robust motion controller. In this paper, we design a closed-loop controller-observer pair for regulating the position of microagents. The prescribed performance technique is applied to control the microagents to follow desired motion trajectories. The position of the microagents are obtained using microscopic images and image processing. The velocities of the microagents are obtained using an iterative learning observer. The algorithm is tested experimentally on spherical magnetic microparticles that have an average diameter of 100 m. The steady-state errors obtained by the algorithm are 20 m. The errors converge to the steady-state in approximately 8 second

Modeling and Control of a Magnetic Drug Delivery System

Therapeutic operation risk has been reduced by the use of micro-robots, allowing highly invasive surgery to be replaced by low invasive surgery (LIS), which provides an effective tool even in previously inaccessible parts of the human body. LIS techniques help delivering drugs effectively via micro-carriers. The micro-carriers are divided into two groups: tethered devices, which are supported by internally supplied propulsion mechanism, and untethered devices. Remote actuation is the critical issue in micro-device navigation, especially through blood vessels. To achieve remote control within the cardiovascular system, magnetic propulsion offers an advantage over other proposed actuation methods. In the literature, most research has focused on micro-device structural design, while there is a lack of research into design and analysis of combined structure and control. As the main part, integrating the principle of electromagnetic induced force by feedback control design will lead to the desired automatic movement. An actuator configuration should thus first be designed to initiate the desired force. The design is basically defining the type and placement of a set of coils to achieve an operational goal. In this project, the magnetic actuation is initiated by a combination of four electromagnets and two sets of uniform coils. Preliminary studies on 2D navigation of a ferromagnetic particle are used to show the effect of actuator structure on controller performance. Accordingly, the performance of the four electromagnets combination is compared to the proposed augmented structure with uniform coils. The simulation results show the improved efficiency of the augmented structure. In more general cases, the arrangement and number of electromagnets are unknown and should be defined. An optimization method is suggested to find these variables when the working space is maximized. Finally, the problem of robust output regulation of the electromagnetic system driven by a linear exosystem, is also addressed in this project. The exosystem is assumed to be neutrally stable with unknown frequencies. The parallel connection of two controllers, a robust stabilizer and an internal model-based controller, is presented to eliminate the output error. In the latter one, an adaptation is used to tune the internal model frequencies such that a steady-state control is produced to maintain the output-zeroing condition. The robust regulation with a local domain of convergence is achieved for a special class of decomposable MIMO nonlinear minimum-phase system. The simulation results show the effectiveness and robustness of this method for the electromagnetic system when two different paths are considered

Design and Implementation of a Fuzzy Controller for Steering Microparticles Inside Blood Vessels by Using a MRI System

RÉSUMÉ Le présent mémoire porte sur l’étude de la conception et la réalisation d’un contrôleur flou avec une seule entrée et multiples sorties. Une telle étude vise à pouvoir contrôler un appareil clinique d’Imagerie par résonance magnétique (IRM) pour fournir des forces de pilotage dans le but de naviguer une microparticule ferromagnétique ou une agrégation de ces microparticules le long d’une trajectoire prédéfinis à l’intérieur du système cardio-vasculaire humaine. L’algorithme de ce contrôleur a été proposé sur un modèle mathématique du fluide dynamique, et sa validité a été vérifiée par les résultats préliminaires de simulations en 2-D générés avec les logiciels MATLAB et C++. À l’aide d’un IRM clinique, des expériences de navigation en temps réel sur des petites perles ainsi que des microparticules ont également été réalisées dans un flux pulsatile. Connexes données expérimentales peuvent prouver que, malgré certaines limites, ce type de contrôleur flou a le potentiel pour devenir le contrôleur approprié appliqué à la navigation par résonance magnétique (NRM).----------ABSTRACT In this thesis, a Single-Input-Multiple-Output (SIMO) fuzzy controller is designed to drive an upgraded clinical real-time Magnetic Resonance Imaging (MRI) machine to provide steering forces for a single microparticle and an aggregation of ferromagnetic microparticles in the human cardiovascular system according to a pre-defined pathway. Based on a fluid dynamic mathematical model, the validity of this kind of controller has firstly been tested by preliminary 2-Dimensional (2-D) simulation results with MATLAB/C++ hybrid programming. With both the beads and real microparticles, real-time experiments were also performed with simulated Magnetic Resonance (MR) sequences and 2-D pulsatile flow. Related experimental data also illustrates that, despite some limitations, this kind of fuzzy controller has the potential to be the appropriate controller for Magnetic Resonance Navigation (MRN)

Magnetic Drug Targeting: Developing the Basics

Focusing medicine to disease locations is a needed ability to treat a variety of pathologies. During chemotherapy, for example, typically less than 0.1% of the drugs are taken up by tumor cells, with the remaining 99.9% going into healthy tissue. Physicians often select the dosage by how much a patient can physically withstand rather than by how much is needed to kill all the tumor cells. The ability to actively position medicine, to physically direct and focus it to specific locations in the body, would allow better treatment of not only cancer but many other diseases. Magnetic drug targeting (MDT) harnesses therapeutics attached to magnetizable particles, directing them to disease locations using magnetic fields. Particles injected into the vasculature will circulate throughout the body as the applied magnetic field is used to attempt confinement at target locations. The goal is to use the reservoir of particles in the general circulation and target a specific location by pulling the nanoparticles using magnetic forces. This dissertation adds three main advancements to development of magnetic drug targeting. Chapter 2 develops a comprehensive ferrofluid transport model within any blood vessel and surrounding tissue under an applied magnetic field. Chapter 3 creates a ferrofluid mobility model to predict ferrofluid and drug concentrations within physiologically relevant tissue architectures established from human autopsy samples. Chapter 4 optimizes the applied magnetic fields within the particle mobility models to predict the best treatment scenarios for two classes of chemotherapies for treating future patients with hepatic metastatic breast cancer microtumors