Design and control of a permanent magnet-based robotic system for navigating tetherless magnetic devices in viscous environments.

Tetherless magnetic devices (TMDs) that are driven using external stimuli have potential applications in minimally invasive surgery. The magnetic field produced by electromagnet- and permanent magnet-based robotic systems is a viable option as an external stimulus to enable the motion of a TMD in viscous and viscoelastic media. In order to realize the navigation of TMDs in fluidic environments, we design a permanent magnet-based robotic system with an open configuration using two synchronized rotating magnetic dipoles to generate time-varying rotating magnetic fields. These fields are used to apply torque on a TMD in low-Reynolds-number flow regimes. The configuration of the system is vertically symmetric, allowing permanent magnets to exert relatively uniform magnetic fields within the center of the workspace. We derive the configuration-to-pose kinematics and the pose-to-field mapping of the system. Such derivation is the basis for realizing the motion control of TMDs in three-dimensional space. The kinematic system holds one translational degree of freedom (DOF) and three rotational DOFs, allowing it to control the pose of actuator magnets with four DOFs. The nonlinear inverse kinematic problem is solved using an optimization algorithm. The experimental results of this level of control demonstrate that the mean absolute error and the maximum tracking error of three-dimensional motion control are 1.18 mm and 2.64 mm, respectively. This paper tackles the challenge of generating and controlling synchronized rotating magnetic fields to actuate and navigate TMDs. Commonly, this involves collaboratively manipulating two permanent magnets by attaching each to the end-effector of an industrial robot. This paper proposes a novel approach: robotically manipulating two permanent magnets through a symmetric configuration constrained by a connecting plate. This method simplifies the manipulation of rotating magnetic fields, thereby aiding the simplification of TMD motion control strategies. Future research will improve the design of this robotic system to offer more degrees of freedom, thus achieving greater flexibility in TMD motion control.