• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.1761-1766
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• 2004

Recently, Plastic optical products are widely used. Injection molding process has advantages of low cost and high productivity. However, it remains a residual birefringence and residual stress by difference cooling. The present study focused on measuring birefringence in optical plastic parts using interference color pattern. The main idea of an analysis comes from chromatic aberration which is caused by difference light wavelengths. As a result, a complete system measuring the high order 2-D birefringence pattern was built. Further investigation is under way to improve the accuracy of birefringence measurement system by diode laser.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2011년도 춘계학술발표대회
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• pp.37.1-37.1
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• 2011

Miniaturization of lenses has been widely researched by various scientific and engineering techniques. As a result, micro scaled lens structure could be easily achieved from various fabrication techniques; nevertheless it is still challenging to make nano scaled lenses. This paper reports a novel fabrication method of silicon nanotemplate for nanolens array. The inverse structure of nanolens array was fabricated on silicon substrate by reactive ion etching (RIE) process. This technique has a flexibility to produce different tip shapes using different pattern masks. Once the silicon nano-tip array structure is well-defined using an optimized recipe, it is followed by polymer molding to duplicate nanolens array from the template. Finally, the nanostructures formed on silicon nanotemplate and polymer replica were investigated using FE-SEM and AFM measurements. The nano scaled lens can be manufactured from the same template, also using other replication techniques such as imprinting, injection molding and so on.

• Design & Manufacturing
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• 제7권1호
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• pp.60-63
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• 2013

Recently, Silicone that one of the thermo-sets is used to making optical products such as LED lenses because of excellent thermal properties. LED lenses are required to keep the precise dimensions, so they must be molded to have the minimum deformation. Thermo-sets have the expansion characteristic on the part of thermal property, it is important to optimize the cure condition so that the deformation of the part become minimum. In this study, to investigate the relationship between the shrinkage by the curing and expansion by the thermal properties of the resin, reactive injection experiment was performed by setting the variables such as mold setting temperature, cure time. As a result, it was confirmed that there was a interval while the thermal properties were transferred to more active during the cure process. It is expected to help in determining the reactive injection molding conditions of the thermo-set parts as well as LED lens in order to reduce the amount of deformation.

• Korea-Australia Rheology Journal
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• 제19권4호
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• pp.191-199
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• 2007

Precision injection molding process is of great importance since precision optical products such as CD, DVD and various lens are manufactured by those process. In such products, birefringence affects the optical performance while residual stress that determines the geometric precision level. Therefore, it is needed to study residual stress and birefringence that affect deformation and optical quality, respectively in precision optical product. In the present study, we tried to predict residual stress, final shrinkage and birefringence in injection molded parts in a systematic way, and compared numerical results with the corresponding experimental data. Residual stress and birefringence can be divided into two parts, namely flow induced and thermally induced portions. Flow induced birefringence is dominant during the flow, whereas thermally induced stress is much higher than flow induced one when amorphous polymer undergoes rapid cooling across the glass transition region. A numerical system that is able to predict birefringence, residual stress and final shrinkage in injection molding process has been developed using hybrid finite element-difference method for a general three dimensional thin part geometry. The present modeling attempts to integrate the analysis of the entire process consistently by assuming polymeric materials as nonlinear viscoelastic fluids above a no-flow temperature and as linear viscoelastic solids below the no-flow temperature, while calculating residual stress, shrinkage and birefringence accordingly. Thus, for flow induced ones, the Leonov model and stress-optical law are adopted, while the linear viscoelastic model, photoviscoelastic model and free volume theory taking into account the density relaxation phenomena are employed to predict thermally induced ones. Special cares are taken of the modeling of the lateral boundary condition which can consider product geometry, histories of pressure and residual stress. Deformations at and after ejection have been considered using thin shell viscoelastic finite element method. There were good correspondences between numerical results and experimental data if final shrinkage, residual stress and birefringence were compared.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2007년도 추계학술대회 논문집
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• pp.454-454
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• 2007

Eye Glass Display (EGD) with microdisplay to realize the virtual display can make the large screen, so virtual image has been developed by using microdisplay panel. This paper shows study of spherical prism lens design and manufacture of a small size and light weigh EGD with 0.59" OLED panel. Code V is used and it designed an aspherical prism lens about eye relief 25mm and 42 degree of filed of view (FOV). With the application this aspheric prism lens to OLED type's microdisplay, virtual image showed 60 inch at 2m. It had less than 2% of distortion value and modulation transfer function in axial had 30% of resolution with 32 lp/mm spatial frequency. We made an injection molding bases to lens designed.

• 폴리머
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• 제32권6호
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• pp.501-508
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• 2008

렌즈나 휴대폰 부품 같은 소형 플라스틱 부품들은 일반적으로 다수 캐비티 사출금형에서 성형된다. 이러한 다수 캐비티 금형에서의 사출성형은 캐비티간의 충전 불균형이 일어날 수 있다. 이러한 충전 불균형 현상은 제품의 치수 및 중량의 편차뿐 아니라 제품의 물리적 특성에도 영향을 미친다. 충전 불균형은 무엇보다도 기하학적으로 균형 잡히지 않은 delivery system의 설계에서 기인된다. 하지만 delivery system이 기하학적으로 균형 있게 설계가 되었다 하더라도 충전 불균형 현상은 여전히 발생된다. 이러한 현상은 런너 단면에서의 온도분포에 기인하며 사출성형 공정 중 사출속도에 크게 영향을 받는 것으로 본 연구에서 파악되었다. 즉 충전 불균형은 부적절한 사출 성형 공정에 의해 발생되며 성형 공정 조건 중 사출속도는 충전에 영향을 주는 매우 중요한 요소이다. 본 연구에서는 재료와 사출 속도에 따른 충전 불균형 현상을 실험과 CAE을 통하여 관찰하였다. 사출속도 변화에 따른 충전 불균형 때문에 시편의 치수 및 무게가 불균일함을 확인하였다.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2012년도 추계학술대회 논문집
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• pp.43-44
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• 2012

본 논문에서는 도로조명용 LED 이차광학계의 제조공정에서 발행하는 형상오차를 설계에 반영하여 제작 후 형상 정밀도를 높여 궁극적으로 도로조명의 조명율을 향상시키는 방법을 제시하였다. 이를 통하여 동일한 에너지를 소모로도 더 높은 광밀도를 가질수 있는 LED2 차렌즈의 제조방법을 제시하였다.

• 한국기계가공학회지
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• 제7권4호
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• pp.17-23
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• 2008

Development of die technology for holder and barrel dies is necessary according to minimization of lens assembly, image sensor, and connectors. In these cases, there are two technical problems arising from die design. One is determination of knock-out pin location in die set. Minimization of lens assembly size make it difficult to obtain ejecting space. The other is whether or not high-precision die technology is possible to reduce torque variation when holer and barrel products is assembled. In this study, multi-cavity die set was developed taking advantage of gear-driven ejecting method. In the developed technology, die manufacturing technology was guaranteed with a high-precision level.

• 한국기계가공학회지
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• 제14권3호
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• pp.36-42
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• 2015

The aspherical lens was designed to be able to array a focal point. For this reason, it has very curved surface. The aspherical lens is fabricated by injection molding or diamond turning machine. With the aspherical lens, tool marks and surface roughness affect the optical characteristics, such as transmissivity. However, it is difficult to polish free form surface shapes uniformly with conventional methods. Therefore, in this paper, the ultra-precision polishing method with MR fluid was used to polish an aspherical lens with 4-axis position control systems. A Tool path and polishing mechanism were developed to polish the aspherical lens shape. An MR polishing experiment was performed using a generated tool path with a PMMA aspherical lens after the turning process. As a result, surface roughness was improved from $R_a=40.99nm$, $R_{max}=357.1nm$ to $R_a=4.54nm$, $R_{max}=35.72nm$. Finally, the MR polishing system can be applied to the finishing process of fabrication of the aspherical lens.

• 한국시뮬레이션학회논문지
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• 제23권4호
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• pp.131-142
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• 2014

휴대폰 카메라의 렌즈 모듈은 경통, 복수의 렌즈, 복수의 스페이서와 한 장의 쉴드로 구성된다. 렌즈 모듈을 생산하기 위한 주요 공정으로는 사출성형공정, 코팅공정 및 조립공정이 있는데, 일반적으로 제조라인에서는 동일한 기능을 가지는 복수의 기계들을 사용하여 생산을 한다. 본 논문에서는 긴급주문, 금형의 파손, 장비의 고장 등으로 인하여 제조현장에서 빈번하게 발생하는 재스케줄링의 문제를 해결하기 위해 시뮬레이션을 기반으로 개발된 스케줄러에 대해 소개한다. 스케줄링 알고리즘은 경험적 Backward-Forward 방법을 사용하였으며, 주문의 납기지연율을 최소화시키는 것이 목표다.