MULTI-DEGREES-OF-FREEDOM WIRELESS ACTUATION OF SMALL MAGNETIC MECHANISMS

Magnetic millimeter-scale robots are often actuated using externally generated magnetic fields. For most applications, these remote magnetic microrobots are located relatively far from the magnetic field generation sources. In this condition, all microrobots receive approximately the same driving magnetic field, which we term a homogeneous magnetic field. For many microrobotic tasks such as drug dispensing, biopsy tool activation or grasping, multiple system degrees of freedom (DOF) must be controlled. To achieve multi-DOF control in a homogeneous magnetic field, clever system design is required. While some progress has been made in this area allowing up to six independent DOFs to be individually commanded, there has been no rigorous effort in determining the maximum achievable number of DOFs for systems with homogeneous magnetic field input. In this work, we show that this maximum is eight and we introduce the theoretical basis for this conclusion, relying on the number of independent usable components in a magnetic field at a point. To verify the claim experimentally, we first develop an electromagnetic field generation system capable of generation all the eight independent magnetic components at a single point, followed by a simple 8-DOF demonstration mechanism, to show the feasibility of eight independently actuated motions. Next, we introduce a design process to utilize the maximum number of independently actuated DOFs on a microrobot system. We make use of four classes of microrobotic mechanisms which are commonly used in practice and allow for the creation of more complex microrobotic mechanisms with up to eight actuated DOFs. The systematic design framework is presented in the form of an optimization problem, where the designer specifies the number of magnets, and the type and quantity of mechanisms of the microdevice. The result gives the optimized position and orientation of on-board magnets and axes for mechanism motion. To verify the functionality of the design process, we utilize it to develop a 7-DOF wireless robot for drug delivery applications. Next, to investigate the feasibility of utilizing magnetic actuation methods in minimally invasive surgery procedures, a 3-DOF wireless gripper prototype and an 8-DOF two-grippers mechanism will be presented. The method and design process presented here for achieving up to eight actuated DOFs in homogeneous quasi-static magnetic fields can be applied to any microrobotic system where multiple motions and on-board mechanisms can lead to a more effective system.Ph.D