Xiang Li; Chien Chern Cheah
In existing control methods for optical tweezers, the trapping stiffness is usually assumed to be constant and known exactly. However, the stiffness varies according to the size of the trapped particle and is also dependant on the distance between the center of the laser beam and the particle. It is, therefore, difficult to identify the exact model of the trapping stiffness. In addition, it is also assumed that the entire workspace is visible within the field of view (FOV) of the microscope. During trapping and manipulation, certain image features such as the desired position may leave the FOV, and therefore, visual feedback is not available. In this paper, a robotic setpoint control technique is proposed for optical manipulation with unknown trapping stiffness and limited FOV of the microscope. The proposed method allows the system to operate beyond the FOV and perform trapping and manipulation tasks without any knowledge of the trapping stiffness. The stability of the overall system is analyzed by using Lyapunov-like method, with consideration of the dynamics of both the cell and the manipulator of laser source. Experimental results are presented to illustrate the performance of the proposed method.
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