• 한국기계가공학회지
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• 제11권3호
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• pp.7-12
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• 2012

Ceramic core processing technology using 5-axis high-speed cutting machine is applied to make the glass molds for aspherical ophthalmic lenses. In the technology, optimum processing conditions for aspherical ceramic molds are based on minimal experimental data of surface roughness. Such surface roughness is influenced by fabricating tools, cutting speed, feed rate, and depth of cut, respectively. In this paper, we present that surface roughness and shape accuracy of aspheric ceramic mold obtained by optimum processing conditions are Pa $0.6184{\mu}m$ and Pt $5.0301{\mu}m$, respectively, and propose that these values are sufficiently possible to apply to making the glass molds for aspherical ophthalmic lenses.

• 한국기계가공학회지
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• 제19권2호
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• pp.69-74
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• 2020

In this study, we proposed a method for surface profiling aspheric lens molds using a precision displacement sensor with a spatial scanning mechanism. The precision displacement sensor is based on the confocal principle using a broadband light source, providing a 10 nm resolution over a 0.3 mm measurable range. The precision of the sensor, depending on surface slope, was evaluated via Allan deviation analysis. We then developed an automatic surface profiling system by measuring the cross-sectional profile of a lens mold. The precision of the sensor at the flat surface was 10 nm at 10 ms averaging time, while 200 ms averaging time was needed for identical precision at the steepest slope at 25 deg. When we compared the measurement result of the lens mold to a commercial surface profiler, we found that the accuracy of the developed system was less than 90 nm (in terms of 3 sigmas of error) between the two results.

• 한국생산제조학회지
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• 제19권2호
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• pp.267-274
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• 2010

Recently, the magnetorheological (MR) polishing process has been examined as a new ultra-precision polishing technology for mirror surface generation in many applications, such as aspheric lenses, biochips, micro parts, etc. This method uses MR fluids which contains micro abrasives as a polishing media, and can. It is possible to obtain nano level surface roughness under suitable process conditions, however, required polishing time is highly dependent on the applied pre-polishing methods due to its very small material removal rate. Thus, in this study, a combined polishing method is presented to reduce total polishing time for SUS304. First, the electropolishing (EP) method was applied to obtain fine surface roughness, and the MR polishing was followed. Surface roughness variations were investigated according to the process conditions. As the results of this study, it was possible to reduce total polishing time for SUS304 using the proposed combined polishing method.

• 한국생산제조학회지
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• 제19권2호
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• pp.184-190
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• 2010

Recently, the polishing process using magnetorheological fluids(MR fluids) has been focused as a new ultra-precision polishing technology for micro and optical parts such as aspheric lenses, etc. This method uses MR fluid as a polishing media which contains required micro abrasives. In the MR polishing process, the surface roughness and material removal rate of a workpiece are affected by the process parameters, such as the properties of used nonmagnetic abrasives(particle material, size, aspect ratio and density, etc.), rotating wheel speed, imposed magnetic flux density and feed rate, etc. The objective of this research is to predict MRR according to the polishing conditions based on the multiple regression analysis. Three polishing parameters such as wheel speed, feed rates and current value were optimized. For experimental works, an orthogonal array L27(313) was used based on DOE(Design of Experiments), and ANOVA(Analysis of Variance) was carried out. Finally, it was possible to recognize that the sequence of the factors affecting MRR correspond to feed rate, current and wheel speed, and to determine a combination of optimal polishing conditions.

• 한국표면공학회지
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• 제44권5호
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• pp.213-219
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• 2011

Recently aspheric lenses are widely used for superpricision optical instruments, such as cellular phone camera modules, digital cameras and optical communication modules. The aspherical lenses are processed using mold core under high temperature compressive forming pressure. It is imperative to develop superhard protective films for the life extension of lens forming mold core. Especially ta-C films with higher $sp^3$ fractions receive attentions for the life extension of lens forming mold and, in turn, the cost reduction of lenses due to their suprior high temperature stability, high hardness and smooth surfaces. In this study ta-C films were processed on WC mold as a function of substrate bias voltage using FVA (Filtered Vacuum Arc) method. The processed films were characterized by Raman spectroscopy and nano-indentation to investigate bonding nature and hardness, respectively. The film with maximun 87% of $sp^3$ fraction was obtained at the substrate bias voltage of -60 V, which was closest to ta-C film. ta-C films showed better high temperature stability by sustaining relatively high fraction of $sp^3$ bonding even after 2,000 glass lens forming applications.

• Journal of the Optical Society of Korea
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• 제18권5호
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• pp.574-581
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• 2014

This paper presents the design and evaluation of the optical zoom system for an LWIR camera. The 12.8operating wavelength range of this system is from $7.7{\mu}m$ to $12.8{\mu}m$. Through a paraxial design and optimization process, we have obtained the extended four-group inner-focus zoom system with focal lengths of 10 to 100 mm, which consists of the six lenses including four aspheric surfaces and two diffractive surfaces. The diffractive lenses were used to balance the higher-order aberrations, and its diffraction properties were evaluated by scalar diffraction theory. We have calculated the polychromatic integrated diffraction efficiency and the MTF drop generated by background noise. The f-number of the zoom system is F/1.4 at all positions. Fields of view are given by $51.28^{\circ}{\times}38.46^{\circ}$ at wide field and $5.50^{\circ}{\times}4.12^{\circ}$ at narrow field positions. In conclusion, this design procedure results in a $10{\times}$ compact zoom lens system useful for an LWIR camera.

• 중소기업융합학회논문지
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• 제6권3호
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• pp.85-91
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• 2016

이 논문의 목적은 낮은 화소 수나 어두운 렌즈를 사용하는 CCTV는 자동차의 번호판이나 범죄자를 인식하기 어렵기 때문에 화소수를 높이고 밝은 렌즈를 사용하기 위함이다. 구면수차와 왜곡수차를 줄이기 위하여 2매의 비구면 렌즈를 적용하고 300만 화소에 적절한 줌렌즈의 설계와 이에 의한 특성을 제시하였다. 초점거리는 6-60mm를 적용하였고 F수는 1.2를 구현하였다. 적외선 보정을 실시하여 주야 초점거리가 같도록 설계하였다. 결과적으로 이 규격은 6-60mm 10배줌 렌즈의 규격 중 가장 우수하다. 이 렌즈를 적용한다면 50m거리에서 얼굴이나 차번호의 인식이 가능하다. 향후 이 렌즈의 자동화 구현이 필요하다.

• 한국광학회지
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• 제6권3호
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• pp.178-187
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• 1995

렌즈 설계에 적합한 감쇠계수를 결정하는 방법을 연구하였다. 구해진 감쇠계수를 additive 감쇠최소 자승법에 도입하였을 때, triplet형 사진렌즈 설계에서 최적화 과정의 수렴성과 안정성에 관해서 조사하였다. 오차함수의 Jacobian 행열의 곱에 대한 고유값을 SVD(singular value decomposition)를 통해 구한 후 고유값들의 중간치를 적합한 감쇠계수로 결정하였다. 적합한 감쇠계수를 이용하여 triplet형 사진렌즈를 최적화한 결과 수렴성과 안정성이 향상되었다. 직교변환 방법으로 Jacobian 행열의 해를 구하면 정규 방정식을 사용하여 해를 구할 때 발생하는 수치적 부정확성을 개선할 수 있었다. 적합한 감쇠계수 선택법과 Jacobian 행열의 직교변환 방법을 같이 사용하는 것이 고차의 항들을 가지는 비구면 렌즈 설계에 유용함을 알 수 있었다.

• Journal of the Optical Society of Korea
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• 제16권3호
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• pp.243-246
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• 2012

An off-axis four-mirror-anastigmatic telescope is presented here which is composed of two aspheric surfaces and two spherical surfaces. The entrance pupil diameter is 290 mm and the stop is located at the primary mirror. The effective focal length is 900 mm. The strip field of view for the telescope is $15^{\circ}{\times}0.2^{\circ}$ and if the telescope is launched into an orbit about 400 km altitude, the observed range width will be more than 105 km within a scene without any other auxiliary scanning instrument. The spectral range can be as wide as from visual wave band to infrared wave band in the mirror system. This telescope can be used for environmental monitoring with different detectors whose pixel is adapted to the optical resolution. In this paper, the spectral range is chosen as 3.0 -5.0 ${\mu}m$, and center distance of the pixel is 30 ${\mu}m$. And the image quality is near the diffraction limit.

• 한국우주과학회:학술대회논문집(한국우주과학회보)
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• 한국우주과학회 2010년도 한국우주과학회보 제19권1호
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• pp.25.3-25.3
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• 2010

Our previous study used a bar-type reference mirror to measure the relative distance to the target surface. The target measurement accuracy was required to $1{\mu}m$ PV for aspheric optical surface up to 1m in diameter. Earlier system suffers from the reference surface deformation when the measuring part moves. In order to reduce the deformation, measuring part and the reference part separated from each order in the new design. This system utilizes a kinematic support assembly using invar flexure to minimize the reference surface deformation under gravity and vibration. The surface deformation requirement of reference mirror is defined as of $0.2{\mu}m$ under gravity and 40Hz vibration. The finite element results, shows reference mirror deformation of $0.164{\mu}m$. The first resonance mode was computed to analysis 46.05Hz for reference part and 43.44Hz for measuring part. Thesis satisfies the frequency requirement.