An automated focusing method for a parallel micro-manipulator alignment

In this work, particle swarm optimization (PSO) algorithm is employed to align spot array and judging image sharpness with auto-focusing (AF) image evaluation function. To satisfy the requirement of optical alignment system, a high precision manipulator has to be developed. Applied parallel manipulator that consists of four 2-degree of freedom (DOF) decoupled actuator gives chances to provide 6-DOF independence motion, and has strength in high accuracy. This paper covers the follows: Firstly, motivation of this development for the digital mirror device (DMD) based maskless lithography system to introduce spot array method in maskless digital exposure process. Secondly, in order to precisely control moving platform, applying a redundant parallel micro-manipulator. Thirdly, proposing a suitable error model of the system and applying the PSO and Z axis auto-focusing algorithm to align spot array concerning position correction. Finally, we designed experiment which is applied a vision sensor and alignment unit to verify proposed positioning algorithm. Experimental result will be shown that proposed can solve the alignment problem by reducing the position error of the system.