Six-Degrees-of-Freedom Remote Actuation of Magnetic Microrobots

Abstract

Abstract—Existing remotely-actuated microrobots powered by magnetic coils far from the workspace exhibit a maximum of only five-degrees-of-freedom (DOF) actuation, as creation of a driving torque about the magnetization axis is not achievable. This lack of orientation control limits the effectiveness of existing microrobots for precision tasks of object manipulation and orientation for ad-vanced medical, biological and micro-manufacturing applications. This paper presents a magnetic actuation method that allows these robots to achieve full six-DOF actuation by allowing for a non-uniform magnetization profile within the microrobot body. This non-uniform magnetization results in additional rigid-body torques to be induced from magnetic forces via a moment arm. A general analytical model presents the working principle for continuous and discrete magnetization profiles. Using this model, microrobot design guidelines are introduced which guarantee six-DOF actuation capability. Several discrete magnetization de-signs which possess reduced coupling between magnetic forces and induced rigid-body torques are also presented. A simple permanent-magnet decoupled prototype is fabricated and used to quantitatively demonstrate the accuracy of the analytical model in a constrained-DOF environment and qualitatively for free motion in a viscous liquid three-dimensional environment. Results show that desired forces and torques can be created with high precision and limited parasitic actuation, allowing for full six-DOF actuation using limited feedback control. I.