Research On Some Problems Of Laser Radius Compensation For Stereolithography

Because a resin area cures under the scanning of moving laser, so the path of laser center is not along the original contour. To get the path of laser center, contours must be shifted toward the interior area with a distance of half the cured width. This process is called laser radius compensation. Radius compensation is one of the key techniques in stereolithography. It is important for the precision of cured parts in stereolithography.First, the original contour must be modified and small concave contours were deleted. Second, offset was implemented for every curve. Last, vertexes of the offset contour were calculated. The offset contours may have self-intersections. Self-intersections must be calculated and contours must be reconstructed.To improve the efficiency of self-intersection calculating, this paper presents a new algorithm based on monotone chains. In this algorithm, intersection detecting was processed only between two current lines, one from the active monotone chain and the other from the inactive monotone chain. So the times for calculating were reduced.For the reconstructing of self-intersection loops, a new criterion was proposed. It helped to reduce the difficulty for invalid loop identifying. In the process of intersection calculating among different loops, rectangular bounding box was used to find the curves which had the chances for intersecting. This helped to simplify the process for intersection identifying.After removing the invalid loops, cured contours always had great difference from the original contours. A scanning style which contained variable radius compensation and variable scanning speed was proposed. In one slice, two kinds of radius compensation and correspondingly two kinds of scanning speeds were adopted when the laser scanned different areas. This can improve the precision and ensure the strength of cured parts.