• Journal of Astronomy and Space Sciences
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• v.27 no.2
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• pp.173-180
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• 2010

As a preparatory study for Global Positioning System-Very Long Baseline Interferometry (GPS-VLBI) hybrid system, we examined if VLBI type observation of the GPS signal is realizable through a test experiment. The test experiment was performed between Kashima and Koganei, Japan, with 110 km baseline. The GPS L1 and L2 signals were received by commercial GPS antennas, down-converted to video-band signals by specially developed GPS down converters, and then sampled by VLBI samplers. The sampled GPS data were recorded as ordinary VLBI data by VLBI recorders. The sampling frequency was 64 MHz and the observation time was 1 minute. The recorded data were correlated by a VLBI correlator. From correlation results, we simultaneously obtained correlation fringes from all 8 satellites above a cut-off elevation which was set to 15 degree. 87.5% of L1 fringes and 12.5% of L2 fringes acquired the Signal to Noise Ratios which are sufficient to achieve the group delay precision of 0.1nsec that is typical in current geodetic VLBI. This result shows that VLBI type observation of GPS satellites will be readily realized in future GPS-VLBI hybrid system.

• Journal of Sensor Science and Technology
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• v.16 no.4
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• pp.270-276
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• 2007

A location-aware system, which is capable to detect a user's whereabout in a region and provide real-time location information in outdoor environment is designed and fabricated, specifically using the GPS (global positioning system) as key technology in view of its stability and high precision in outdoor environment. Experiment is conducted to test this application in campus-based environment. Once GPS receiver detects specific location which is tagged with GPS coordinates, the system provides information relevant to that context and user can operate and react accordingly. Besides, this location-aware system is able to provide user with the route in order to get to a desired place by detecting the direction that the user is moving towards from his/her initial location. The mapping data is transferred via wireless LAN to PDA carried by the user as well as to the back-end system on real-time basis. The test result is analyzed and discussed to validate the effectiveness of using GPS in implementing this system and indicates future works that could be made to improve this prototype to be implemented in other applications, such as theme park, tourist attraction spot or recreational park.

• Journal of Positioning, Navigation, and Timing
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• v.7 no.4
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• pp.277-284
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• 2018

The Satellite-based Augmentation System (SBAS), as a safety critical system, should be verified on an ongoing basis to ensure the adequate performance. This study proposes two methods to evaluate the performance of SBAS satellite correction. Analysis methods based on precise ephemeris and measurement were applied to present an evaluation method for SBAS satellite correction, and a test was performed based on real data. The precise ephemeris-based analysis method had no limitations on the position of the test user and showed a high precision, enabling an accurate performance analysis in various positions. Although the measurement-based analysis method has the advantage of fast data interval, it showed a relatively lower accuracy due to the effects of various error factors. Compared with the precise ephemeris-based analysis method, there was a large difference of more than 5 m at the beginning of smoothing filter, and a difference less than 50 cm when filtered for more than an hour.

• 제어로봇시스템학회:학술대회논문집
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• 2004.08a
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• pp.301-306
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• 2004

In this study, Dual servo mechanism with VCM(Voice Coil Motor) and PZT is designed for a high precision force and position control. We designed the VCM actuator and dual servo mechanism with leaf spring. VCM actuators, with their high linearity, simple structure, low weight, and high efficiency, are increasingly being used in micro-positioning applications. There are many kinds of VCM with a structure. VCM actuators are divided into two types by moving parts. One is moving magnet type and the other moving coil type. We described the properties of these two types of VCM. Design parameters of VCM are defined through the FEM simulation analysis of magnetic field and dynamic model of dual servo mechanism. These researches help to for decreasing loss in the air gap of VCM. We present dual servo mechanism is effective mechanism for a force control in hi h precision, properties of designed VCM.

• Journal of the Korean Society for Precision Engineering
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• v.24 no.3 s.192
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• pp.67-75
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• 2007

This paper deals with a problem of vibration suppression of a piezoelectric beam using a self-sensing algorithm. Two methods, which are PPF(positive position feedback) and SRF(strain rate feedback), are considered to suppress a residual vibration of a piezoelectric beam developed during the step positioning of a beam end point. A self-sensing algorithm treated here is basically a strain rate estimator of a beam movement and is to be used for the closed loop control. The efficacy of the proposed idea is evaluated through experiments.

• Journal of the Korean Society for Precision Engineering
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• v.19 no.6
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• pp.184-191
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• 2002

This paper presents the thermal behavior of a synchronous linear motor with high speed and force. Such a linear motor can successfully replace ball lead screw in machine tools because it has a high velocity, acceleration and good positioning accuracy. On the other hand, low efficiency and high heating up during operation are disadvantage of linear motors. For the application of linear motors to machine tools a water-cooling system is often used. In this research, structure of the linear motor and water cooler is changed to improve the thermal behavior of the linear motor. Some important effects of an integrated cooler, an U-cooler and a thermally symmetrical cooler are presented.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.10a
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• pp.894-897
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• 2004

In this paper, we address a position control scheme for a stage system, which is levitated and driven by electric magnetic actuators. This consists of a levitating object (called platen) with 4 permanent magnetic linear synchronous motors in parallel. Each motor generates vertical force for suspension against gravity and propulsion force horizontally as well. This stage can generate six degrees of freedom motion by the vertical and horizontal forces. Dynamic equations of the stage system are derived based on Newton-Euler method and its special Jacobian matrix describing a relation between the Joint velocity and platen velocity is done. There are proposed two control schemes for positioning, which are Cartesian space controller and Joint space controller. The control performance of the Cartesian space controller is better than the Joint space controller in task space trajectory while the Joint space controller is simpler than the Cartesian space controller in controller realization.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 1999.10a
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• pp.560-564
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• 1999

Burr sensing for burr size measurement and deburring process control is one of the essential elements in an automated deburring procedure. This paper presents the implementation of capacitance sensing and acoustic emission (AE) to deburring. The first application is the "on-line" measurement of burrs using a capacitance sensor. A non-contact capacitance gauging sensor is attached to an ultra precision milling machine which was used as a positioning system. The setup is used to measure burr profiles along machined workpiece edges. The proposed scheme is shown to be accurate, easy to setup, and with minor modifications, readily applicable to automatic deburring processes. As the second example, AE signals were sampled and analyzed for the sensor feedback of a precision deburring process - laser deburring -. The results, such as the sensitivity of AE signals to burr shapes and edge detection capability show a clear correlation between physical process parameters and the AE signals. A subsequent control strategy for deburring automation is also briefly discussed.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2000.10a
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• pp.193-199
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• 2000

Control system for cutting piston used in vehicle that is one of the 3D shape cutting using CNC lathe is presented. In order to cut the hybrid piston shape using CNC lathe, defined piston shape and change into machine code. The control software was developed for the high speed piston shape cutting. In this paper, the performance of this software was evaluated practically. As a result, the evaluated cutting precision was quantitatively compared with theoretical precision. Also the productivity and the quality by using CNC lathe with control software were evaluated those by using profiling.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 1995.03a
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• pp.40-62
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• 1995

A micro positioning system using piezoelectric actuators have very wide application region such as ultra-precision machine tool optical device measurement system. In order to keep a high precision displacement resolution it to useful to take a position sensor and feedback of the error. From the practical point of view high-resolution displacement sensor systems are very expensive and it is difficult to make such a sensitive sensor work properly in a poor operational environment of industry. In this study a piezo-electric micro-depth control system which does not require position sensor but piezoelectric voltage feedback has been developed. It is driven by hysteresis-considering reference input voltage calculated in advance and actuator/sensor characteristics of piezoelectric materials. From the result of experiments a fast and stable response of micro-depth control system has been achieved and an efficient technique to control the piezoelectric actuator suggested.