• Journal of the Korean Society for Precision Engineering
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• v.30 no.12
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• pp.1321-1325
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• 2013

In this paper, we proposed an air bearing stage with active magnetic preloads in vertical directions compensating motion errors and attenuating vibrations to improve dynamic characteristics. This preloaded design gives simpler configuration of the stage, and active control of preload can be used for compensating motion errors by feedforward method. To improve dynamic characteristics, vibration of the table is monitored by an accelerometer, and controlled by a DSP based digital controller with integrator and band pass filters for suppressing roll and pitch vibration modes. The modes were evaluated by measuring frequency response functions, and compared with compensated responses. This showed effective results for suppressing poorly damped regenerative vibration of air bearings.

• Journal of KSNVE
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• v.8 no.3
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• pp.450-456
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• 1998

A rotordynamic analysis is performed with a centrifuge rotor-bearing system for the raing speed of 100,000 rpm. The system is composed of a centrifuge rotor(or simply the rotor), flexible shaft, motor rotor and shaft, and two support rolling element bearings of the motor shaft. Design goals are to achieve wide separation margins of critical speeds and favorable unbalance responses of the rotor at the associated critical speeds. The latter requirements are especially important as the system crosses multiple numbers of critical speeds and as the system may not have enough separaton margins around the rating speed. As the system adopts an extra-flexible shaft, it is shown that the rotor has satisfactory small unbalance responses over higher criticals while having an unsatisfactory large one at the first critical. To supress this a bumper ring or guide bearing needs to be installed at a suitable location of the flexible shaft. It is also shown that even with the flexible shaft the dynamics of the motor must be incoporated into the full system model to accurately identify the fourth critical speed, which is close to the rating speed, and higher ones. The analysis is based on the finite element method.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.1561-1569
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• 2000

Flying attitudes of the slider, which are flying height, pitch and roll, are affected by the air flow velocity, the skew angle, and the manufacturing tolerances. Traditional designs of the air bearing surface have considered only the flying performances for the variations in the air flow velocity and the skew angle, which are determined by the radial position. In this study, we present the new shape design of the air bearing surface by considering the track seek performance and the air bearing stiffness as well as the traditional design requirements. The optimization technique is used to improve the dynamic characteristics and operating performance of the newly proposed air bearing surface shape design further. The optimized configuration is obtained automatically and the optimally designed sliders show the enhanced flying and dynamic characteristics.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.19 no.11
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• pp.1214-1221
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• 2009

A high-speed spindle can be very sensitive to rotating mass unbalance which has harmful effect on many machine tools. Therefore, the balancing procedure to reduce vibration in rotating system is certainly needed for all high-speed spindles. So, balancing procedure was performed with a spindle-bearing system for CNC automatic lathe by using numerical procedure. The spindle is supported by the angular contact ball bearings and the motor rotor is fixed at the middle of spindle. The spindle-bearing system has been investigated using combined methodologies of finite elements and transfer matrices. The balancing was performed through influence coefficient method and the comparison was made by whirl responses between before balancing and after balancing. As a result, balancing of simple spindle model reduced whirl orbit magnitude in case of a completely assembled spindle model.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.23 no.3
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• pp.234-239
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• 2013

There are many types of speed reducer for industrial uses. However the cycloid speed reducer is widely used in manipulators based on excellent performance of low backlash, high reduction ratio and compact size. It is essential to use precision speed reducer for accuracy of position controls on robot systems and electric vehicles. The cycloid speed reducer has a eccentric rotating motion and offset to avoid some problem of assembly, so it has a disadvantage for vibration. In this paper, a multi-body dynamic model is developed for a cycloid speed reducer and the dynamic behaviors of the reducer are investigated. The cycloid speed reducer consists of cycloidal plate gears, housing gear, input shaft, output pin and shaft, and eccentric bearings. Using a CAD program, each component of cycloid reducer is modeled based on the offset and eccentric. Multi-body simulations using Recurdyn and test using a rig tester are performed. As a result, the pin reaction force and the amplitude of housing displacement are increased by the larger offset and smaller eccentric value of cycloid reducer.

• Journal of the Korean Society for Precision Engineering
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• v.22 no.11 s.176
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• pp.142-150
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• 2005

Design and performance evaluation of a spindle system which was composed of a grinding spindle and a regulating spindle for the centerless grinding of ferrule were performed in this paper. Layout and details of spindle system were designed and hydrostatic bearings for spindles were also designed. Prototype of spindle system was developed and its availabilities to machine the ferrule were discussed using the experimental results on the spindle stiffness of each spindle, loop stiffness, rotational accuracy and thermal characteristics. Loop stiffness of the spindle system was $130\;N/{\mu}m$, which was enough to machine the ferrule. Rotational accuracies of each spindle were about $0.2{\mu}m$ at the primary speed of 2,300 rpm(grinding spindle) and 300 rpm(regulating spindle). Temperature rises at the same speed were about $4.4\~4.7^{\circ}C$ in the case of grinding spindle and $1.8^{\circ}C$ in the case of regulating spindle, which agreed well with the designed value. From these results, it was estimated that the prototype of spindle system had enough performances for the centerless grinding machine to machine the ferrule.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1995.06a
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• pp.54-64
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• 1995

대표적인 대형 베어링인 일체형 볼 베어링과 와기어 레이스형 볼 또는 로울러 베어링의 마찰 특성을 비성형 유한요소 프로그램인 MARC를 사용하여 상호간의 마찰형상에 대한 접촉응력과 마찰력 특성을 비교 해석하였다. 특히 와이어 레이스식 슬루잉 링 베어링은 우수한 마찰특성 때문에 건설기계, 하역기계, 광산기계나 탱크와 같은 국방무기 등에서 널리 사용되고 있다. 접촉면의 변형에 따른 일체형의 볼 베어링은 마찰력과 기울기면에서 와이어 레이스식 베어링에 비하여 크고, 같은 와이어 레이스식 베어링에서는 마찰력의 경우 볼 타입이 로울러 탕입에 비하여 약간 크게 나타났다. 이들의 계산결과를 종합하면 와이어 레이스식 베어링이 일체형 베어링에 비하여 마찰특성이 우수하고, 특히 와이어 레이스 베어링중에서 로울러 타입은 마찰 토오크면에서 균일하기 때문에 베어링을 사용한 제어기능 설계에서 특히 우수한 결과를 제공할 수 있다. 유한요소 해석결과는 기존의 실험결과와 잘 일치하고 있어서 슬루잉 링 베어링의 최적설계에 유한요소 해석의 유용함을 확인하였다. 또한 상부 구조물과 하부 구조물을 연결하기 위한 체결볼트의 구멍은 하중조건에 따라서 구조적 불안정성을 야기할 수 있음도 확인하였다.

• Tribology and Lubricants
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• v.23 no.2
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• pp.66-72
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• 2007

[ $MoS_2$ ], is a well-known metal sulfide applied as solid lubricants and an additive to prolong the life of sintered bearings under severe conditions. However, the high price of $MoS_2$ limited its wide application. This study is aimed to investigate the possibility far application to solid lubricants for $Cu_2S$ as a substitute of $MoS_2$. Bronzes added $Cu_2S$ and $MoS_2$, are produced by powder metallurgy in this study, and then evaluated their friction and wear properties., as well as sintered bronze. The sliding wear test using pin-on-disc type machine, was conducted at several sliding speeds for three type test pieces sintered bronzes added $Cu_2S$ and $MoS_2$, and sintered bronze without lubricants. Addition of $Cu_2S$ to bronze leads to relatively good friction properties, although it is not so good as addition of $MoS_2$. However, the wear properies of sintered bronze added $Cu_2S$ are better than that of sintered bronze added $MoS_2$.

• Journal of Institute of Control, Robotics and Systems
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• v.21 no.1
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• pp.65-69
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• 2015

A vision-based blank alignment unit for a press automation line is introduced in this paper. A press is a machine tool that changes the shape of a blank by applying pressure and is widely used in industries requiring mass production. In traditional press automation lines, a mechanical centering unit, which consists of guides and ball bearings, is employed to align a blank before a robot inserts it into the press. However it can only align limited sized and shaped of blanks. Moreover it cannot be applied to a process where more than two blanks are simultaneously inserted. To overcome these problems, we developed a press centering unit by means of vision sensors for press automation lines. The specification of the vision system is determined by considering information of the blank and the required accuracy. A vision application S/W with pattern recognition, camera calibration and monitoring functions is designed to successfully detect multiple blanks. Through real experiments with an industrial robot, we validated that the proposed system was able to align various sizes and shapes of blanks, and successfully detect more than two blanks which were simultaneously inserted.

• Journal of the Korean housing association
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• v.15 no.5
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• pp.107-118
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• 2004

The purpose of this study is to analyze the unique characteristics of the vernacular house of Ulleung-Do(island), which shows a different residential culture from the main land. For this purpose, this study examined the characteristics of the location, spatial arrangement, and floor-plan of the house and also tried to understand how these basic elements were changed and why these changes were occurred. The result of this study is as follows: First, the house was located on the mountain area and was oriented toward the various bearings. Second, the house usually did not have annexes and most residential space was installed on a main building. Third, the floor-plan of the house was developed from a basic two-Kan (with single row) house type in a early settlement period to three-Kan, four-Kan, and five-Kan house types in later periods. While the development of house type proceeded. the main building was functioned as a complex space for both residential and storage purposes. Some houses were gradually developed into a middle and upper-class house shape by installing annexes. The change of the floor-plan and the house size was the result of self-sustained living culture influenced by the natural environment of the island and of changes of residential conditions as well.