• 한국측량학회지
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• 제19권1호
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• pp.9-17
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• 2001

차량의 항법 뿐만아니라 측지 및 측량분야에서 그 효율성이 입증되고 있는 GPS는 준 도시지역과 같이 장애물이 있는 경우 최소 위성수 확보가 힘든 단점이 있다. 재정적 문제로 완전한 위성배치를 이루고 있지 않은 구 소련의 위성항법시스템인 GLONASS는 위치결정원리. 신호체계 등에서 GPS와 많은 유사점을 갖고 있으며, GPS와 조합된다면 많은 이점이 있을 것으로 기대된다. 본 연구에서는 GPS/GLONASS 조합에 의한 절대측위 정밀도를 분석하여 항법 및 측지분야에서 그 효율성을 제시할 목적으로, GPS와 GLONASS에 대한 기준좌표계, 시간 및 주파수 체계의 특성을 고찰하고, 좌표계 및 주파수의 상이로 인해 발생하는 문제점을 해결하여 절대측위 알고리즘을 정립하였다. 그리고, C/A 코드와 Yuma 위성궤도정보를 이용하여 GPS/GLONASS 통합에 의한 절대측위 정밀도를 분석하였다.

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2006년도 International Symposium on GPS/GNSS Vol.2
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• pp.185-190
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• 2006

The correct estimation of the ionospheric delays is very important for the precise kinematic positioning especially in case of the long baseline. In case of triple frequency system, the ionospheric delays can be estimated from the measurements, but, in case of dual frequency system, the situation is not so simple. The precision of those supplied by the external information source such as IONEX is not sufficient. The high frequency component is neglected, and the precision of the low frequency component is not sufficient for the long baseline positioning. On the other hand, the high frequency component can be estimated from the phase range measurements. If the low frequency components are estimated by using the external information source or pseudo range measurements, a more reasonable estimation of the ionospheric delays may be possible. It has already been discussed by the author that the estimation of the low frequency components by using the external information source is not sufficient but fairly effective. The estimation using the pseudo range measurements is discussed in the present paper. The accuracy is not sufficient at present because of the errors in the pseudo range measurements. It is clarified that the bias errors in the pseudo range measurements are responsible for the poor accuracy of the ionospheric delays. However, if the accuracy of the pseudo range measurements is improved in future, the method would become very promising.

• Journal of Positioning, Navigation, and Timing
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• 제12권4호
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• pp.349-358
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• 2023

The Satellite-Based Augmentation System (SBAS) plays a significant role in the fields of aviation and navigation: it corrects signal errors of the Global Navigation Satellite System (GNSS) and provides integrity information to facilitate precise positioning. These SBAS systems have been adopted as international standards by the International Civil Aviation Organization (ICAO). In recent SBAS system design, the Minimum Operational Performance Standards (MOPS) defined by the Radio Technical Commission for Aeronautics (RTCA) must be followed. In October 2014, South Korea embarked on the development of a Korean GPS precision position correction system, referred to as Korea Augmentation Satellite System (KASS). The goal is to achieve APV-1 Standard of Service Level (SoL) service level and acquisition of CAT-1 test operating technology. The first satellite of KASS, KASS Prototype 1, was successfully launched from the Guiana Space Centre in South America on June 23, 2020. In December 2022 and June 2023, the first and second service signals of KASS were broadcasted, and full-scale KASS correction signal broadcasting is scheduled to start at the end of 2023. The aim of this study is to analyze the precision of both the GNSS system and KASS system by comparing them. KASS is also compared with Japan's Multi-functional Satellite Augmentation System (MSAS), which is available in Korea. The final objective of this work is to validate the usefulness of KASS correction navigation in the South Korean operational environment.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2004년도 추계학술대회 논문집
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• pp.890-893
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• 2004

The ultra precision machining in industrial field are increased day by day. The diamond turning has been used generally, but now is faced with limitation of use, because of higher requirement of production field. The electron beam lithography is alternative in machining area as semiconductor production. For EB lithography, 5 axis vacuum stage is required to duplicate small and large patterns on wafer. The stage is composed of 2 rotational axis and 3 translational axis with 5 DC servo motors. The positioning repeatability and resolution of Z axis feed unit are 3.21$\mu$m and 0.5 $\mu$m/step enough to apply to lithography.

• 한국정밀공학회지
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• 제24권8호통권197호
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• pp.89-96
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• 2007

In this paper, a new air bearing stage with magnetic preload and a linear motor has been developed for the small precision machine systems. The new air bearing stage is unique in the sense that permanent magnets attached bottom of the iron core of table are used not only for preloading air bearings in vertical direction but also for generating thrust force by current of the coil at base. The characteristics of air bearings using porous pads were analyzed with numerical method, and the magnetic circuit model was derived for linear motor for calculating required preload force and thrust force. A prototype of single axis miniature stage with size of $120(W){\times}120(L){\times}50(H)\;mm^3$ was designed and fabricated and examined its performances, vertical stiffness, load capacity, thrust force and positioning resolution.

• International Journal of Precision Engineering and Manufacturing
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• 제9권1호
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• pp.19-24
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• 2008

We propose a new miniature air-bearing stage with a moving-magnet slotless linear motor. This stage was developed to achieve the precise positioning required for submicron-level machining and miniaturization by introducing air bearings and a linear motor sufficient for mesoscale precision machine tools. The linear motor contained two permanent magnets and was designed to generate a preload force for the vertical air bearings and a thrust force for the stage movement. The characteristics of the air bearings, which used porous pads, were analyzed with numerical methods, and a magnetic circuit model was derived for the linear motor to calculate the required preload and thrust forces. A prototype of a single-axis miniature stage with dimensions of $120\;(W)\;{\times}\;120\;(L)\;{\times}\;50\;(H)\;mm$ was designed and fabricated, and its performance was examined, including its vertical stiffness, load capacity, thrust force, and positioning resolution.

• 한국정밀공학회지
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• 제9권4호
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• pp.44-57
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• 1992

Ball screw systems have been used for positioning elements of machine tools and precision tables. In order to maintain the high rigidity and accuracy, a certain amount of preload is applied between the nut and the screw of ball screw systems. However, large amount of the preload oncreases the frictional heat. The temperature rises remarkably at the high speed motion, and the thermal expansion degrades the positioning accuracy. In this paper, a finite difference method is applied to analyse temperature distributions and thermal expansions of the ball screw system according to preload conditions and rotational speeds. Some simulation results show that the developed methodology is appropriate to study the thermal expansion characteristics of ball screw systems.

• 지구물리
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• 제7권4호
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• pp.325-330
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• 2004

For the monitoring of structures, it is desirable for the measurement system to deliver equal precision in all components. When using GPS the accuracy, availability, reliability and integrity of the position solutions is very dependent on the number and geometric distribution of the available satellites. Therefore the positioning precision is not the same in all there component, and large variations (in positioning) precision can be expected during a 24-hour period. This situation becomes worse when the line-of-sight to GPS satellites becomes obstructed, such as in urban environments. Pseudolites can be sed to augment GPS and improve a geometrically weak satellite constellation. The use of pseudolites as supplement(s) of GPS for the movement measurement of bridges is demonstrated in this paper. It is shown that pseudollites can improve the vertical position components.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2000년도 추계학술대회 논문집
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• pp.85-88
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• 2000

In this paper, the ultra precision positioning system for piezoelectric actuator using hysteresis compensation has been developed. Piezoelectric actuators exhibit limited accuracy in tracking control due to their hysteresis nonlinearity. The main purpose of the proposed controller is to compensate the hysteresis nonlinearity of the piezoelectric actuator. The controller is composed of a PD, hysteresis compensation and neural network part in parallel manner, at first, the excellent tracking performance of the neural network controller was verified by experiments and was compared with the classical PD controller.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1994년도 추계학술대회 논문집
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• pp.254-259
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• 1994

Recently, the precision ball screw becomes the essence of the high-precision industries and is playing a key role in the positioning devices. The standard and definition of pitch error in a precision ball screw is specified by KS, JIS or ISO. However, the method of measuring the pitch error is not concrete. In this study. laser measurement system(LMS) with a laser position transducer and a machine-tools is developed. In order to verify the stability of the LMS, several experiments with the standard ball screw is performed.