Design of polygonal mirror-based laser scanning optics for fast & highly precise stereolithographic apparatus

Abstract

This study designs polygonal mirror-based laser scanning optics for a stereolithographic 3D printer with a fast scanning speed and higher resolution than conventional systems. The optics can scan focused laser light on a 300 mm wide image width with a highly confined beam spot less than 60 mu m in the full-width 1/e(2)-maximum of the beam spot profile. To achieve the imaging performance on a resolution, rotationally asymmetric F-theta lenses defined by high-order polynomials were designed to achieve a larger effective scan angle, which can yield a compact optical system. The designed optical system showed a performance of 60 +/- 3 mu m at the full width of the 1/e(2) maximum intensity value through a focal depth of 3 mm. The scanning linearity error and root-mean-squared wavefront error were designed to be less than 1 dot and 0.03 lambda, respectively. Furthermore, to evaluate the fabrication feasibility of each optical component of the designed F-theta optics, the effect on the optical performance of potential fabrication error items such as the decenter and the tilt of each optical component are analyzed. A tolerance analysis confirmed that the optical surface of each lens has sufficient tolerance for decenter and tilt errors. Although the error of rotation with respect to the optical axis of L2, gamma, has the smallest tolerance as much as 0.16 degrees, Delta(by gamma) caused by gamma as much as 0.16 degrees exceeds 300 mu m. The designed optical system capable of high-speed scanning with uniform physical characteristics is expected to significantly improve the building precision and speed of the desktop stereolithographic apparatus.