• 한국정밀공학회지
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• 제25권8호
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• pp.45-50
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• 2008

An ink jetting measurement system has been developed such that the velocity as well as the volume of ink droplets can be measured. In order to measure the ink droplet, a strobe LED light was synchronized to the droplet firing signal in order to obtain frozen droplet images. Then, a LabVIEW based software was developed for the analysis of the droplet image. For the efficient droplet analysis, a user generated rectangular shaped ROI (Region of Interest) was used. By using ROI, the ink droplet image can be easily isolated from the other structures such as printhead and the processing area can be minimized.

• 한국전산유체공학회지
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• 제17권2호
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• pp.65-70
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• 2012

The droplet ejection behavior from drop-on-demand printhead are investigated numerically in terms of the non-dimensional parameters. The numerical simulation is performed using a volume-of-fluid model. It is important to eject droplet within the printability range, where the droplet is ejected in stable manner without satellite droplets. Generally, the printability range has been determined by Z number, which is the inverse of Oh number. However, it is found that the ejection of droplets with same Z number can exhibit different behavior depending on the value of Ca and We number. Therefore, it is insufficient to determine the printability range only with Z number. Instead, other non-dimensional parameters, such as Ca and We number, should be considered comprehensively.

• 한국정밀공학회지
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• 제23권7호
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• pp.168-176
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• 2006

Nowadays, Three dimensional printing (3DP) technique that is one of solid freeform fabrication (SFF) technology has been notable issue, and has been applied by various fields. The SFF system can fabricate three dimensional objects of solid freeform with high speed and low cost using ink jet printing technology. In this research, a SFF system to analyze 3DP process technology is developed. We applied sliding mode control with sliding perturbation observer (SMCSPO) algorithm and minimized position error to the developed SFF system. We analyzed and optimized process variables such as jetted volume, layer thickness, powder bed and so on experimentally. Also. the dimensional error of a developed SFF system is evaluated. Finally, the feasibility of application to bio manufacturing is presented through successful fabrication of teeth and cranium model.

• 대한기계학회논문집B
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• 제31권6호
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• pp.558-565
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• 2007

Many studies of microdroplet evaporation from solid surfaces were made with priority given to inkjet printing and dye painting techniques. The objective of these studies is how to evaporate a droplet quickly and uniformly. Also it is necessary to prevent evaporation of a droplet to observe cells in a droplet generated through cell-patterning. In general, an identical volume of a water droplet on hydrophobic surfaces evaporates slower than that on hydrophilic surfaces. In this study, we observe the evaporation process of a droplet on various hydrophobic surfaces and calculated the evaporation rate considering the droplet geometry such as contact angle and height. This study also proposes a new model based on the fact that evaporation mode at the edge of a droplet is different from that at the outer surface of a droplet as the contact angle changes during evaporation. Finally, we reveal the cause fur the increase of evaporation flux and show that the ratio of edge evaporation to total evaporation increases with time.

• 한국전산유체공학회지
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• 제17권3호
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• pp.33-38
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• 2012

The droplet ejection behavior from drop-on-demand printhead are investigated numerically for Newtonian and shear-thinning fluid. The numerical simulation is performed using a volume-of-fluid model. In this study, we compare the printable range in terms of Z number and pinch-off time for Newtonian and shear-thinning fluids. The printability range are found to be 1.08 $$\leq_-$$ Z $$\leq_-$$ 12.9 for Newtonian fluid and 0.8 $$\leq_-$$ Z $$\leq_-$$ 12.9 for shear-thinning fluid. However, air entrainment is observed during merging of primary and satellite droplet within the printability range. The pinch-off time of the shear-thinning fluid is apparently shorter compared to the corresponding Newtonian fluid due to shear-thinning effects and the differences in the pinch-off time is enlarged significantly when the capillary number is larger than 0.5.

• 청정기술
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• 제7권3호
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• pp.169-178
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• 2001

섬유염색은 전 세계적으로 매우 큰 시장이나, 염료를 사용하여 섬유염색을 수행하는 기존 인쇄 공정의 경우 염료의 손실 및 환경오염의 문제점을 갖고 있다. 기존 공정들의 경우 섬유 인쇄 시 전처리 및 후처리 공정이 필요하고 이들 공정에서 폐수가 발생하게 된다. 이런 문제점들의 해결방안으로 전처리 및 후처리 공정이 필요없고 잉크를 효율적으로 사용할 수 있는 잉크제트 프린팅 기법을 섬유염색 기술에 적용하려는 노력이 진행중이다. 섬유인쇄를 위해 잉크제트 프린터를 사용할 경우 안료를 사용하기 때문에 잉크는 액체 상에 고체입자가 분산되어 있는 서스펜션 상태로 존재한다. 분자역학 모사 기법과 유사한 Stokesian 역학 모사 방법을 사용한 전산모사를 통해 외부에서 가해진 압력구배에 의해 노즐 관에 흐르는 분산잉크 중의 입자 분포 및 속도 분포 변화를 살펴보았다. 전산모사결과 입자의 부피분율이 낮을수록, 평균 무차원 서스펜션 속도가 낮을수록, 노즐 관과 입자 크기 사이의 비(H/a)가 클수록 입자들의 분포가 상당히 균일한 것으로 나타났다. 따라서 잉크제트 프린팅 기법을 사용하여 섬유인쇄를 수행하는 경우, 노즐 관에의 유속을 작게 하고 노즐 관과 입자 사이의 크기 비를 크게 해야 균일한 인쇄 성능을 얻을 수 있을 것으로 판단된다.