One of the current trends in commercial PBF-type 3D printers is to enlarge the printing (or building) area in pursuit of the productivity enhancement and the printability of large parts. To increase the printing area, 3D printer manufacturers installed multiple (2 or 4) galvano scanners, each of which is paired with an f-θ lens with a long focal length. Since a longer focal length of an f-θ lens means both positively a wider printing area and negatively a larger spot diameter of laser beam. The larger the spot diameter, the poorer the resolution of the printed parts. To address the tradeoff, we proposed a new PBF-type 3D printing process in which a galvano scanner and a polygon scanner are sequentially moving across the powder bed. In this paper, we discussed the signal synchronization between a polygon scanner and a diode laser.