In the industry, three-dimensional coloring has been needed for realistic prototype from rapid prototyping. Z-corporation developed a 3D printer which provides three-dimensional colored prototype. However, the existing process cannot be adopted to models from other rapid prototyping process. In addition, time and cost for manufacturing colored prototype still remain to be improved. In this study, a new coloring process using ink-jet head is proposed for color printing on three-dimensional prototype surface. In order to print an image on the three-dimensional surface, process parameters such as the angle and the distance between ink-jet nozzle and the three-dimensional surface should be investigated from experiments. Through the experiment for these process parameters, it has been shown that the distance and the angle affect the printed image on a sloped surface. Circles and lines were chosen as standard shapes because the shape has been widely used as standard shape in 2D printing. The critical distance which results in accurate printing was obtained. The correction matrix according to sloped angle to minimize the distortion of 2D image was proposed by analysis of printing error. The proposed matrix was verified by printing `KAIST' logo on the sloped surface. In order to investigate the distortion of printed image on the curved surface, experiments were carried out by printing images on the ruled surface. It has been found that the printing error on the curved surface is similar to that on the sloped surface at each angle. Therefore, approximated method for angle and discrete length according to the radius of curvature for printing on the curved surface was proposed. The curved surface was divided into several discrete sections within the error range to apply the correction matrix of sloped angle. By printing image on the doubly curved surface, the method was verified. As a practical example, helmet was chosen for printing images on the curved surface. The grid data to find feasible printing area was printed on the helmet having doubly curved surface. The character images were applied with approximated method for angle and discrete length and was printed on the helmet surface. From this result, it has been shown that the correction matrix can be applied to general images on curved surfaces.
산업에서 시작품의 실감재현을 위한 3차원 칼라링 기술이 필요하다. 그러나 기존의 3차원 표면에 칼라를 재현하는 기술은 다른 시작품에 채색할 수 없으며 시간과 비용이 많이 소요된다. 본 연구에서는 잉크젯 헤드를 이용하여 3차원 표면에 채색을 하는 새로운 공정을 제안한다. 공정 개발을 위해 잉크젯 헤드와 기울어진 면사이의 거리와 각도에 따른 인쇄 특성에 대한 실험을 수행하였다. 실험 결과 공정 변수에 따라 인쇄 오차를 최소화할 수 있는 보정 행렬을 제안하고 검증하였다. 곡면에 대한 프린트 특성을 알아보기 위해 선곡면에 대한 실험을 수행하였으며 3차원 곡면 인쇄를 위해 곡률에 따른 단속 거리와 각도를 제안하였다. 이러한 개념은 곡면에서 오차 범위내에 드는 몇 개의 단속적인 분할을 수행하여 분할 곡면을 기울어진 면으로 근사하여 보정 행렬에 따라 이미지를 왜곡하는 것이다. 최종적으로 헬멧 표면에 일반적인 이미지 프린팅 실험을 수행하여 본 연구의 실용성 검증할 수 있었다.
