• Journal of Engineering Education Research
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• v.13 no.2
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• pp.28-32
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• 2010

The mechanical clock was designed and produced by students as a trial theme of PBL class. The limit of making time is three weeks and main material is limited to paper. Only a basic mechanism drawing is given. As the principle of mechanical clock is not complex and does not need the special knowledge of mechanical engineering, even lower grade student seems to understand enough. This subject can train the skill of knowledge composition, creativity and the problem-solving ability. After execution,the validity and performance as the theme of PBL class was evaluated. As a result, the following findings were obtained. The paper made mechanical clock could be produced in three weeks. And, by additional improvements of the product, the enough strength and stable movement were achieved. Students can learn that many kinds of knowledge through actual experiences of design and making were required in manufacturing the real products. The proposed PBL style class is suitable as an introduction and training subject for lower grade student in department of engineering.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• v.1
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• pp.309-314
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• 2006

In general DGPS system, the correction message is transferred to users by wireless modem. To cover wide area, many DGPS station should be needed. And DGPS users must have a wireless modem that is not necessary in standalone GPS. But SBAS users don't need a wireless modem to receive DGPS corrections because SBAS correction message is transmitted from the GEO satellite by L1 frequency band. SBAS signal is generated in the GUS(Geo Uplink Subsystem) and uplink to the GEO satellite. This uplink transmission process causes two problems that are not existed in GPS. The one is a time delay in the uplink signal. The other is an ionospheric problem on uplink signal, code delay and carrier phase advance. These two problems cause ranging error to user. Another critical ranging error factor is clock synchronization. SBAS reference clock must be synchronized with GPS clock for an accurate ranging service. The time delay can be removed by close loop control. We propose uplink ionospheric error correcting algorithm for C/A code and carrier. As a result, the ranging accuracy increased high. To synchronize SBAS reference clock with GPS clock, I reviewed synchronization algorithm. And I modified it because the algorithm didn't consider doppler that caused by satellites' dynamics. SBAS reference clock synchronized with GPS clock in high accuracy by modified algorithm. We think that this paper will contribute to basic research for constructing satellite based DGPS system.

• Publications of The Korean Astronomical Society
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• v.35 no.3
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• pp.43-57
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• 2020

Hong, Dae-Yong manufactured the Tongcheon-ui (Pan-celestial Armillary Sphere) with cooperating clock researcher Na, Kyeong-Jeok, and its craftsman An, Cheo-In, in Naju of Jeolla Province in 1760 ~ 1762. Tongcheon-ui is a kind of astronomical clock with an armillary sphere which is rotated by the force generated by a lantern clock's weight. In our study, we examine the lantern clock model of Tongcheon-ui through its description of the articles written by Hong himself. As his description, however, did not explain the detail of the mechanical process of the lantern clock, we investigate the remains of lantern clocks in the possession of Korea University Museum and Seoul National University Museum. Comparing with the clocks of these museums, we designed the lantern clock model of Tongcheon-ui which measures 115 mm (L) × 115 mm (W) × 307 mm (H). This model has used the structure of the striking train imitated from the Korea University Museum artifact and is also regulated by a foliot escapement which is connected to a going train for timekeeping. The orientation of the rotation of the going train and the striking train of our model makes a difference with the remains of both university museums. That is, on the rotation axis of the first gear set of Tongcheon-ui's lantern clock, the going and the striking trains take on a counterclockwise and clockwise direction, respectively. The weight of 6.4 kg makes a force driving these two trains to stick to the pulley on the twine pulling across two spike gears corresponding to the going train and the striking train. This weight below the pulley may travel down about 560 mm per day. We conclude that the mechanical system of Tongcheon-ui's lantern clock is slightly different from the Japanese style.

• Journal of Positioning, Navigation, and Timing
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• v.8 no.4
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• pp.209-214
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• 2019

Precise point positioning (PPP) requires precise orbit and clock products. International GNSS service (IGS) real-time service (RTS) data can be used in real-time for PPP, but it may not be possible to receive these corrections for a short time due to internet or hardware failure. In addition, the time required for IGS to combine RTS data from each analysis center results in a delay of about 30 seconds for the RTS data. Short-term orbit prediction can be possible because it includes the rate of correction, but the clock correction only provides bias. Thus, a short-term prediction model is needed to preidict RTS clock corrections. In this paper, we used a long short-term memory (LSTM) network to predict RTS clock correction for three minutes. The prediction accuracy of the LSTM was compared with that of the polynomial model. After applying the predicted clock corrections to the broadcast ephemeris, we performed PPP and analyzed the positioning accuracy. The LSTM network predicted the clock correction within 2 cm error, and the PPP accuracy is almost the same as received RTS data.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.7
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• pp.785-797
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• 2014

Support for the precise time synchronization of EtherCAT, known as distributed clock (DC), enables the design of highly synchronized operations in distributed real-time systems. This study evaluates the performance of the EtherCAT DC through extensive experiments in a real automation system. We constructed an EtherCAT control system using Xenomai and IgH EtherCAT stack, and analyzed the clock deviation for different devices in the network. The results of the evaluation revealed that the accuracy of the synchronized clock is affected by several factors such as the number of slave devices, period of drift compensation, and type of system time base. In particular, we found that careful decision regarding the system time base is required because it has a fundamental effect on the master operation, which results in significantly different performance characteristics.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1996.11a
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• pp.702-706
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• 1996

The King Sejong's Striking water-clock was named for its distictive day and night time announcing system. Its time announcing system generates acoustic and visual signals for the twelve double hour, and combinations of two different acoustic signals for the five night watches, The mechanism of this signal generation system is triggered by a copper ball which is mechanically digitized time keeping signal, and is generated from the water clock. The time announcing system consisted four parts: 1) the mechanical amplifier which changes small copper to heavy steel ball, 2) day time announcing system, 3) night time announcing system, 4) sounding mechanism. The time announcing system of King Seong's Striking Clepsidra is remotely related to the Arabic clock system, however, it does have world-widely distictive mechanisms of its era, such as mechanical amplifier, self-weight rachet mechanism, and resetable mechanical computer etc.

• Journal of Advanced Navigation Technology
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• v.13 no.2
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• pp.178-186
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• 2009

SBAS(Satellite Based Augmentation System) provides GNSS satellite orbit and clock corrections for positioning accuracy improvement of GNSS users. In this paper, the accuracy of SBAS satellite orbit and clock corrections were analyzed by comparing with the IGS(International GNSS Service) precise ephemeris. The GPS antenna phase center offsets and the P1-C1 bias are considered for the analysis. The correction data of the US WAAS and the Japanese MSAS were analyzed. The analysis results showed that the SBAS satellite orbit and clock corrections are highly correlated. The correction data accuracy depends on the SBAS ground network size and orbit trajectories.

• 한국전산유체공학회:학술대회논문집
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• 2008.08a
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• pp.71.2-71.2
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• 2008

• Journal of Energy Engineering
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• v.24 no.1
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• pp.1-9
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• 2015

Welding defects affect the performance of welded pipe joints. In this study, a three point bend test of welded steel and medium density polyethylene (MDPE) pipe joints with defects of various defect locations and defect materials was studied using the finite element method. The defect was assumed to be located at 12 o'clock, 3 o'clock or 6 o'clock direction. The results showed that pipes failed more easily on the compression side due to stress or local buckling. The air defect was more dangerous than the steel defect if the defect was located in the compression side; otherwise, the defect material effect on the integrity of pipes was ignorable. It is argued that the integrity of pipes with defects in the compression side is weaker than that in other regions, and the defect should be located in the compression side or the 12 o'clock position in the three point bend test to maximize the effect of defect existence on the pipe structural integrity.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.7
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• pp.4871-4877
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• 2015

This article presents a circuit and a system for IEEE 1588 based clock synchronization to generate a very accurate frequency signal required in femtocell devices. A prototype board and the experimental environment to verify the functions and to evaluate the performance are explained to verify the feasibility of the proposed synchronization system. To make low-cost femtocells without constraints on the place of installation, it is very important to study on the practical implementation of synchronization system based on IEEE 1588. The experimental result shows that the synchronization errors between -16 ns and 9 ns are guaranteed over the network of femtocell devices with the proposed synchronization circuits, thus the synchronization criteria of the 3GPP HNB are met.