Xiang Li; Chien Chern Cheah; Quang Minh Ta
While several control schemes and automation techniques have been proposed for coordination and manipulation of multiple cells using optical tweezers, open-loop control methods are always utilized by treating the positions of lasers as the control inputs instead of feedback variables. As the positions of laser beams are not utilized in feedback control, it is, therefore, assumed in the literature that the multiple cells are always trapped by the laser beams throughout the manipulation task. However, the control techniques fail when the cells are not initially trapped by the laser beams, or when the laser beams move too fast, such that the cells escape from the traps during manipulation. This paper presents a closed-loop control formulation and strategy for optical manipulation of multiple cells, based on the cooperative movement of the motorized stage and the beam steering system. The closed-loop control method enables the trapping operation to be automatically activated whenever the cells are not inside the optical traps. The proposed controller does not require exact knowledge on the dynamic parameters and the varying trapping stiffness. Lyapunov methods are employed in the stability analysis of the optical tweezers system. Experimental results are presented to illustrate the performance of the proposed controller.