• 제어로봇시스템학회논문지
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• 제13권1호
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• pp.72-78
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• 2007

Determination of the local vertical is not trivial for a moving vehicle and in general will require corrections for the Earth geophysical deflection. The vehicle's local vertical can be estimated by INS integration with initial alignment in SDINS(Strap Down INS) system. In general, the INS has drift error and it cause the performance degradation. In order to compensate the drift error, GPS/INS augmented system is widely used. And in the event that GPS is denied or unavailable, celestial navigation using star tracker can be a backup navigation system especially for the military purpose. In this celestial navigation system, the vehicle's position determination can be achieved using more than two star trackers, and the accuracy of position highly depends on accuracy of local vertical direction. Modern tilt sensors or accelerometers are sensitive to the direction of gravity to arc second(or better) precision. The local gravity provides the direction orthogonal to the geoid and, appropriately corrected, toward the center of the Earth. In this paper the relationship between direction of center of the Earth and actual gravity direction caused by geophysical deflection was analyzed by using precision orbit simulation program embedded the JGM-3 geoid model. And the result was verified and evaluated with mathematical gravity vector model derived from gravitational potential of the Earth. And also for application purpose, the performance variation of pure INS navigation system was analyzed by applying precise gravity model.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제11권5호
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• pp.2741-2761
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• 2017

With the purpose of copyright protection for digital video, a novel H.264/AVC watermarking algorithm based on JND model is proposed. Firstly, according to the characteristics of human visual system, a new and more accurate JND model is proposed to determine watermark embedding strength by considering the luminance masking, contrast masking and spatial frequency sensitivity function. Secondly, a new embedding strategy for H.264/AVC watermarking is proposed based on an analysis on the drift error of energy distribution. We argue that more robustness can be achieved if watermarks are embedded in middle and high components of $4{\times}4$ integer DCT since these components are more stable than dc and low components when drift error occurs. Finally, according to different characteristics of middle and high components, the watermarks are embedded using different algorithms, respectively. Experimental results demonstrate that the proposed watermarking algorithm not only meets the imperceptibility and robustness requirements, but also has a high embedding capacity.

• Computers and Concrete
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• 제20권6호
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• pp.719-729
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• 2017

A considerable research is available on the seismic response of Reinforced Concrete (RC) shear wall-frame buildings, but the studies on the reliability of such buildings, with the consideration of human error, are limited. In the present study, a detailed procedure for reliability assessment of RC shear wall-frame building subjected to earthquake loading against serviceability limit state is presented. Monte Carlo simulation was used for the reliability assessment. The procedure was implemented on a 10-story RC building to demonstrate that the shear walls improve the reliability substantially. The annual and life-time failure probabilities of the studied building were estimated by employing the information of the annual probability of earthquake occurrence and the design life of the building. A simple risk-based cost assessment procedure that relates both the structural life-time failure probability and the target reliability with the total cost of the building was then presented. The structural failure probability (i.e., the probability of exceeding the allowable drift) considering human errors was also studied. It was observed that human error in the estimation of total load and/or concrete strength changes the reliability sharply.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2005년도 ICCAS
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• pp.888-893
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• 2005

Since inertial sensor errors which increase with time are caused by initial orientation error and sensor errors(accelerometer bias and gyro drift bias), the accuracy of these devices, while still improving, is not adequate for many of today's high-precision, long-duration sea, aircraft, and long-range flight missions. This paper presents a navigation error compensation scheme for Strap-Down Inertial Navigation System(SDINS) using star tracker. To be specific, SDINS error model and measurement equation are derived, and Kalman filter is implemented. Simulation results show the boundedness of position and attitude errors.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2000년도 추계학술대회논문집 - 한국공작기계학회
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• pp.449-453
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• 2000

In metal cutting, the machining accuracy is more affected by thermal errors than by geometric errors. This paper models of the thermal errors for error analysis and develops on-the-machine measurement system by which the volumetric error are measured and compensated. The thermal error is modeled by means of angularity errors of a column and thermal drift error of the spindle unit which are measured by the touch probe unit with a star type styluses, a designed spherical ball artifact, and five gap sensors. In order to analyze the thermal characteristics under several operating conditions, experiments performed with the touch probe unit and five gap sensors on the vertical and horizontal machining centers.

• 한국방송∙미디어공학회:학술대회논문집
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• 한국방송공학회 2002년도 정기총회 및 학술대회
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• pp.105-109
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• 2002

The main ideas of hybrid video coding methods are to reduce the spatial and temporal redundancy for efficient data compression. If compressed video stream is transmitted through the error-prone channel, bitstream can be critically damaged and the spatio-temporal error propagates through successive frames at the decoder because of drift noise in the references between encoder and decoder. In this paper, I propose the lagrangian multiplier selection method in the error-prone environment. Finally, it is shown that the performance comparisons of the R-D optimized mode decision are made against the conventional method and simulation results are given in the following.

• Journal of the Optical Society of Korea
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• 제16권4호
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• pp.401-408
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• 2012

The amplitude error of phase modulator used in closed-loop fiber optic gyroscope has occurred by the temperature dependency of the electro-optic coefficient, and also can be due to the square-wave dither signal which is generally applied for eliminating the deadzone. This error can cause bias drift and scale factor error. This paper analyzes the temperature dependency of the modulation amplitude and the relationship with the scale factor of the gyroscope, and deals with an amplitude control method. The error calculation logic considering the dither signal is implemented on the signal processing module. The result of experiments from a prototype gyroscope shows the effect of the modulation amplitude control and a considerable improvement on performances.

• Journal of Positioning, Navigation, and Timing
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• 제11권1호
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• pp.35-44
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• 2022

In this paper, a dual foot (DF)-PDR system is proposed for the fusion of integration (IA)-based PDR systems independently applied on both shoes. The horizontal positions of the two shoes estimated from each PDR system are fused based on a particle filter. The proposed method bounds the position error even if the walking time increases without an additional sensor. The distribution of particles is a non-Gaussian distribution to express the lateral error due to systematic drift. Assuming that the shoe position is the pedestrian position, the multi-modal position distribution can be fused into one using the Gaussian sum. The fused pedestrian position is used as a measurement of each particle filter so that the position error is corrected. As a result, experimental results show that position of pedestrians can be effectively estimated by using only the inertial sensors attached to both shoes.

• 천문학회보
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• 제40권1호
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• pp.82.1-82.1
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• 2015

We investigate the long-term spatial drift of the center and the temporal variation of the shutter delay time map of Y4KCam mounted on the CTIO 1.0m telescope. We have collected shutter delay time maps for over 7 years as a part of long-term survey program. We find that the center of the shutter delay time map can drift up to $450{\mu}m$ on the CCD. This effect can result in a small amount of error unless the proper shutter delay time correction, but it does not appear to cause any significant problems in photometric measurements. We obtain the mean value of the shutter delay time of $69.1{\pm}0.9$ msec and find no temporal variation of the shutter delay time of Y4KCam for over 7 years, indicative of the mechanical stability of the shutter. We suggest that using a master shutter delay time correction frame would be sufficient to achieve high precision photometry and this does not add up errors more than ~ 2.5 mmag across the CCD frame with exposure times longer than 1 sec.

• 오토저널
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• 제4권3호
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• pp.48-55
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• 1982

In the present the strain gauge type torque transducers consist of solid shaft as sensor, slip ring, brush and bridge circuit as detecting circuit. So in the case of measuring the low-capacity torque, the error caused by technical mistake in mounting stain gauge on the small sensor and especially by contact resistance between slip ring and brush takes place more than the large sensor. Therefore in this study constant voltage in order to have no effect of contact resistance is supplied to the hollow shaft and Schrobron Bridge Circuit. Through the experiment good results were obtained as follows; linearity, hysterisis and zero drift as static characteristics is within 1% F.S respectively. Also when loading, zero drift is about 2% F.S.