Three-Dimensional Visual Servo Control of a Magnetically Propelled Microscopic Bead

This paper presents the development of a visual servo control system that is capable of trapping and steering a microscopic magnetic bead in a 3-D workspace using a hexapole magnetic actuator. The magnetic actuator employs six sharp-tipped magnetic poles, arranged in a hexagonal configuration, and six actuating coils to achieve 3-D magnetic actuation. Real-time 3-D visual tracking is realized through processing video images acquired by a complementary metal-oxide semiconductor (CMOS) camera to achieve nanometer-scale resolution for particle tracking. A model-based nonlinear control law is developed to achieve two objectives: 1) to stabilize the magnetically propelled microscopic bead and control its Brownian motion and 2) to rapidly steer the microscopic bead within the 3-D workspace. Specifically, 3-D visual servo control of a 2.8-μm magnetic bead is employed to validate the capability of the developed control system. The control performances in terms of variance minimization, 100 nm stepping, and large range steering are experimentally demonstrated.