The development of a magnetic micromanipulation system that is capable of trapping and steering a magnetic microbead in three dimensions is presented in this paper. Hexapole magnetic tweezers were designed and implemented to realize three-dimensional (3D) magnetic actuation. Because magnetic actuation is inherently unstable without feedback control, visual measurement based on computer processing of video images was employed to detect the displacement of the microbead, facilitating real-time feedback control. An analytical magnetic force model was developed to characterize the nonlinearity and position dependency of the magnetic force exerted on the magnetic bead by the hexapole magnetic tweezers. Its inverse model was then derived and employed in feedback linearization. A proportionalintegral controller along with feedback linearization was implemented and the motion of the magnetic bead was successfully stabilized. The control results in terms of 100-nanometer stepping and 3D motion steering were experimentally demonstrated.

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