• Current Optics and Photonics
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• 제7권6호
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• pp.708-713
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• 2023

A robust all-fiber nonlinear amplifying loop-mirror-based mode-locked femtosecond laser is demonstrated. Power-dependent nonlinear phase shift in a Sagnac loop enables stable and power-efficient mode-locking working as an artificial saturable absorber. The pump power is adjusted to achieve the lowest intensity noise for stable long-term operation. The minimum pump power for mode-locking is 180 mW, and the optimal pump power is 300 mW. The lowest integrated root-mean-square relative intensity noise of a free-running mode-locked laser is 0.009% [integration bandwidth: 1 Hz-10 MHz]. The long-term repetition-rate instability of a free-running mode-locked laser is 10^-7 over 1,000 s averaging time. The repetition-rate phase noise scaled at 10-GHz carrier is -122 dBc/Hz at 10 kHz Fourier frequency. The demonstrated method can be applied as a seed source in high-precision real-time mid-infrared molecular spectroscopy.

• Korea-Australia Rheology Journal
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• 제15권3호
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• pp.117-124
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• 2003

Elastohydrodynamic lubrication (EHL) film is measured under the condition of viscosity index improver added to base oil. In-situ optical contact method using the interference principle make the measuring resolution of ~5 nm possible and enables the measuring range all over the contact area of up to ~300 $\mu\textrm{m}$ diameter. What is more important to the developed method by the author is that the measurement of EHL film thickness is possible in the range from 100 nm to 2 $\mu\textrm{m}$, which is the regime of worst contact failures in precision machinery. Viscosity index improver (VII) is one of the major additives to the modem multigrade lubricants for the viscosity stability against temperature rise. However, it causes shear thinning effects which make the film thickness lessened very delicately at high shear rate (over $10^5 s^{-1}$) of general EHL contact regime. In order to exactly verify the VIIs performance of viscosity stability at such high shear rate, it is necessary to make the measurement of EHL film thickness down to ~100 nm with fine resolution for the preliminary study of viscosity control. In this work, EHL film thickness of VII added lubricant is measured with the resolution of ~5 nm, which will give very informative design tool for the synthesis of lubricants regarding the matter of load carrying capacity at high shear rate condition.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2005년도 춘계학술대회 논문집
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• pp.441-445
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• 2005

In the resent years, as the research and the development of micro and precision machinery become active, the interest of micro actuators using SMA(Shape Memory Alloy) has been increased. But, no detailed researches between the thermo-dynamic property in Nitinol alloy have been done yet. In this study, the thermal property of high temperature Nitinol shape memory alloy were evaluated using differential scanning calorimeter(DSC). The structure property was investigated using X-ray diffraction(XRD). A dynamic mechanical analyzer(DMA) with three point bending mode was used to study storage and loss modulus of shape memory alloy according to the thirteen frequencies in the temperature range between 30 and $200^{\circ}C$. The effects of the temperature heating/cooling rate, the frequency on the damping capacity have been systematically investigated. Such a frequency and temperature changes also influenced significantly to the damping behavior of the shape memory alloy. It was also found that Nitinol exhibited high damping capacity during phase transformation.

• 대한기계학회논문집A
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• 제25권1호
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• pp.70-80
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• 2001

A cycloid reducer is one of the rotational velocity reduction equipments of machinery. It has advantages of the higher reduction ratio, the higher accuracy, the easier adjustment of transmission ratio and the smaller workspace than other kinds of reducer. A cycloidal plate gear is a main part of the cycloid reducer. Its tooth shape is peculiar because of gearing with the roller gear that has the several rollers on the circular line. And then it can be designed to contact all teeth to rollers. So, the cycloid reducer has the good characteristics in the dynamic properties and the zero-backlash in the contact motion. It can be used in robots, high-precision machines and high capacity machinery. This paper proposes a new approach for the shape design of the cycloidal plate gear and presents a Computer-Aided-Design program developed by the proposed method. The first part of this paper defines the two types of the cycloid reducers and explains their mechanisms. The second part defines the instant velocity centers for each type of the cycloid reducers and calculates the contact angles and the contact points by using te geometric relationships and the kinematical properties of the reducers. The third part generates the full shape of the cycloidal plate gear by the coordinate transformation technique. Finally, this paper presents two examples for the shape design of the cycloidal plate gear in order to prove the theory of the proposed method in this paper and the accuracy of the \"CycloGear Designer\".

• Journal of Biosystems Engineering
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• 제30권2호
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• pp.127-133
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• 2005

Precision tillage is designed to till lands variably according to their firmness. Therefore, it is necessary to measure soil firmness in fields and present it in a form with which the variable tillage on be performed. Such forms may be classified into two categories: sensor-based and map-based forms. The map-based approach appears to be inevitable until the technology develops high enough to secure the sensor-based approaches. The first step for map-based precision tillage may be to develop a tillage recommendation map. In this study, a tractor-mountable automatic soil firmness measurement system was developed to construct a cone index map. The system is comprised of three ASAE Standard cone penetrometers and a hydraulic unit for controlling operation of the penetrometers. The system is designed to conduct stop-and-go measurements in fields. The measurements from the three penetrometers are transferred to a microcomputer and the average cone index was calculated. This average cone index was taken as soil firmness of the location where the measurement was made. The cone indices thus determined were used to construct a cone index map using the ArcView software. The system also displays the soil penetration resistance, cone index and soil depth as the cone penetrates into the soil. The field performance of the system was evaluated and the cone index maps at different depths were also presented.

• 한국산업융합학회 논문집
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• 제23권6_2호
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• pp.1059-1065
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• 2020

Demand for pressure sensors is increasing in various fields such as machinery, healthcare and medical care. A recent study is being conducted to create sensors that are more sensitive and have longer linear sections based on measurement principles. In this paper, a film-type sensor with a membrane structure was developed to measure the pressure distributed in the axial direction of a hot roll laminator. Performance of sensors was evaluated by resistance and durability according to membrane diameter. The resistance of the membrane sensor varies according to the contact state and contact area of the electrode. Therefore, the membrane diameter selection is important. Experiments showed the most pronounced variation in resistance under pressure at 8 mm in diameter of membrane. Reliability evaluation of sensors was carried out at room temperature and high temperature. The pressure on the sensor was pressurized 1000 times to measure the initial resistance and the resistance after the evaluation to analyze the change. Sensors showed stable results with low resistance changes of 5.15% and 6.27%, respectively. A large area sensor manufactured using the developed sensor also showed reliable results.

• 한국정밀공학회지
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• 제29권1호
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• pp.56-63
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• 2012

Due to the development of construction technology, there is a considerable increase in the number of skyscrapers in the world. Accordingly, there are rapid growing requests about maintenance systems such as cleaning, painting, and monitoring the processes of facade in highrise buildings. However, it is extremely dangerous working the walls of high-rise buildings, and crashes from buildings have accounted for large proportion of constructional accidents. An alternative solution must be developed with the commercialization of automatic robot systems. For the last decade, interest in developing robots for cleaning and maintenance in facade of highrise buildings has continuously increased. The use of automatic robot systems can be expected to reduce accidents and decrease labor costs. In this paper, we propose a new kind of cleaning mechanism. We have designed and manufactured various cleaning tools for different types of facades with economic commercialization. The cleaning cycle, size, and intensity will be determined by economic constraints as well. The final goals are to design and manufacture tools and robots that can clean facades efficiently and rapidly even in dangerous places. The cleaning tool systems consist of nozzles, brush rollers, and squeezing devices. Furthermore, these tools and robots perform each process utilizing the systems of built-in guide types and gondola types for building maintenance. The performance of the proposed cleaning tools is evaluated experimentally; however additional study should be necessary for safer and more stable commercialization.

• Agricultural and Biosystems Engineering
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• 제5권1호
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• pp.10-20
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• 2004

Precision agriculture aims to minimize costs and environmental damage caused by agriculture and to maximize crop yield and profitability, based on information collected at within-field locations. In this process, quantification of soil physical properties, including soil strength, would be useful. To quantify and manage variability in soil strength, there is need for a strength sensor that can take measurements continuously while traveling across the field. In this paper, preliminary analyses were conducted using two datasets available with current technology, (1) cone penetrometer readings collected at different compaction levels and for different soil textures and (2) tillage draft (TD) collected from an entire field. The objective was to provide information useful for design of an on-the-go soil strength profile sensor and for interpretation of sensor test results. Analysis of cone index (CI) profiles led to the selection of a 0.5-m design sensing depth, 10-MPa maximum expected soil strength, and 0.1-MPa sensing resolution. Compaction level, depth, texture, and water content of the soil all affected CI. The effects of these interacting factors on data obtained with the soil strength sensor should be investigated through experiments. Spatial analyses of CI and TD indicated that the on-the-go soil strength sensor should acquire high spatial-resolution, high-frequency ($\ge$ 4 Hz) measurements to capture within-field spatial variability.

• 대한전자공학회논문지SD
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• 제44권1호
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• pp.22-27
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• 2007

반도체 또는 평판디스플레이 제조에 있어 노광공정 후의 PR(photoresist) 제거 공정으로 이용하기 위하여 경계 막 제어에 의한 오존처리공정 및 설비 구현에 대한 연구를 수행하였다. 개발한 초 고농도 오존생성기술과 vapor 발생 방식 경계 막 제어 오존처리공정설비에 의해 실리콘 웨이퍼 PR 제거시험을 수행하였으며 오존가스농도 16wt%, 오존가스 유량 $8[\ell/min]$에서 약 400nm/분의 높은 PR 제거율을 달성하였다.

• 한국기계가공학회지
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• 제2권2호
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• pp.52-59
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• 2003

Cam mechanism is a machine part frequently used in machinery. Specially, conjugate cam mechanism is very suitable for the high speed working and the heavy power translation. Then a conjugate cam mechanism need high precision for the relations between cam profiles and follower rollers. So, its design and manufacturing are very difficult. Thus, this study is a branch of exclusive CAM systems for design and NC machining of conjugate earn mechanism based on a master plate earn profile in order to exchange an old plate cam mechanism to a new conjugate earn mechanism. For the design of the other cam profile by using a master cam profile, some calculation processes were used by vector summation methods, from master cam profile data to the center data of master follower, from the center data of master follower to the center data of the other follower considered in link mechanism, and offsetting in the center direction of base circle of the other cam from the center data of the other follower. Finally, a sample conjugate cam was selected and machined m order to prove the contents of this study.