• 한국정밀공학회지
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• 제32권7호
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• pp.643-651
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• 2015

Multi-axis magnetic and accelerometer sensor are widely used in consumer product such as smart phones. The vector output of multi-axis sensors have errors on each axis such as offset error, scale error, non-orthogonality. These errors cause many problems on the performance of the applications. In this paper, we designed the effective inline compensation algorithm for calibrating of 3 axis sensors using ellipsoid for mass production of multi-axis sensors. The outputs with those kinds of errors can be modeled by ellipsoid, and the proposed algorithm makes sequential mappings of the virtual ellipsoid to perfect sphere which is calibrated function of the sensor on three-dimensional space. The proposed calibrating process composed of four main stages and is very straightforward and effective. In addition, another imperfection of the sensor such as the drift from temperature can be easily inserted in each mapping stage. Numerical simulation and experimental results shows great performance of the proposed compensation algorithm.

• 한국군사과학기술학회지
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• 제19권5호
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• pp.582-589
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• 2016

Multi-mode monopulse system is widely used for satellite terminal like UAV because of high tracking accuracy and low size/weight profile. In order to calculate tracking error, Multi-mode monopulse system utilizes high-order mode signal, and it should have enough C/N(carrier to noise) level therefore tracking system needs narrow band filtering of received satellite beacon signal as much as possible. However, UAV suffers for beacon frequency drift derived from Doppler effect due to satellite figure 8 movement and UAV maneuvering. Therefore wideband signal processing needs to be considered in advance for exact doppler compensation and consequent time delay. In this paper, we propose the multi-stage Digital Signal processing system for beacon signal, which could minimize the signal delay under high Doppler and low C/N condition.

• Journal of Power Electronics
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• 제9권3호
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• pp.438-446
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• 2009

The performance of direct torque controlled (DTC) interior permanent magnet (IPM) machines is poor at low speeds due to a few reasons, namely limited accuracy of stator voltage acquisition and the presence of offset and drift components in the acquired signals. Due to factors such as forward voltage drop across switching devices in the three phase inverter and dead-time of the devices, the voltage across the machine terminals differ from the reference voltage vector used to estimate stator flux and electromagnetic torque. This can lead to instability of the IPM drive during low speed operation. Compensation schemes for forward voltage drops and dead-time are proposed and implemented in real-time control, resulting in improved performance of the space vector modulated DTC IPM drive, especially at low speeds. No additional hardware is required for these compensators.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2005년도 ICCAS
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• pp.241-245
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• 2005

Strapdown inertial navigation system (SINS) integrated with astronavigation system (ANS) yields reliable mission capability and enhanced navigational accuracy for spacecrafts. The theory and characteristics of integrated system based on unscented Kalman filtering is investigated in this paper. This Kalman filter structure uses unscented transform to approximate the result of applying a specified nonlinear transformation to a given mean and covariance estimate. The filter implementation subsumed here is in a direct feedback mode. Axes misalignment angles of the SINS are observation to the filter. A simple approach for simulation of axes misalignment using stars observation is presented. The SINS error model required for the filtering algorithm is derived in space-stabilized mechanization. Simulation results of the integrated navigation system using a medium accuracy SINS demonstrates the validity of this method on improving the navigation system accuracy with the estimation and compensation for gyros drift, and the position and velocity errors that occur due to the axes misalignments.

• 한국공작기계학회논문집
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• 제10권4호
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• pp.70-75
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• 2001

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 spindel unit which are measured by the touch probe unit with a star type styluses, a designed spherical ball arti-fact, 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.

• 대한전자공학회논문지
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• 제4권3호
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• pp.28-33
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• 1967

트란지스터 착동증폭기의 해석은 이등분 정리의 응용으로 간단히 되며 온도 및 전원전압의 변화에 의한 drfit는 자체보상회로에 의해서 감소시킬수 있다. 베스-에미터전압을 같게하는 기본자체보상회로와 이 전압의 온도계수를 같게 하는 온도자체보상회로를 써서 실험하여 양호한 결과를 얻었으며 이 회로의 조절은 이론치와 잘 일치함을 확인하였다.

• Smart Structures and Systems
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• 제14권6호
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• pp.1031-1054
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• 2014

Real-time hybrid simulation (RTHS) of a stacked wood shear wall retrofitted with a rate-dependent seismic energy dissipation device (viscous damper) was conducted at the newly constructed Structural Engineering Laboratory at the University of Alabama. This paper describes the implementation process of the RTHS focusing on the controller scheme development. An incremental approach was adopted starting from a controller for the conventional slow pseudodynamic hybrid simulation and evolving to the one applicable for RTHS. Both benchmark-scale and full-scale tests are discussed to provide a roadmap for future RTHS implementation at different laboratories and/or on different structural systems. The developed RTHS controller was applied to study the effect of a rate-dependent energy dissipation device on the seismic performance of a multi-story wood shear wall system. The test specimen, setup, program and results are presented with emphasis given to inter-story drift response. At 100% DBE the RTHS showed that the multi-story shear wall with the damper had 32% less inter-story drift and was noticeably less damaged than its un-damped specimen counterpart.

• 제어로봇시스템학회논문지
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• 제21권7호
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• pp.669-676
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• 2015

In this paper, we described the simulation results of the phase offset performance of a clock in holdover mode which was normally operated in GPS Disciplined Oscillator (GPSDO). In the TIE model, we included the time error term caused by environmental temperature variation because one of the most important parameters of clock phase error is the frequency offset and drift caused by the variation of temperature. For the simulation, we employed Maximum Time Interval Error (MTIE) for the performance evaluation when the frequency offset and drift are estimated by using an Unbiased Finite Impulse Response (UFIR) filter with ladder algorithm. We assumed that the noise in the GPS measurement is white Gaussian with zero mean and 1 ns standard deviation, and temperature linearly varies with a slope of $1{^{\circ}C}$ per hour. From the simulation results, the followings were observed. First, with the estimation error of temperature of less than 3 % and the temperature compensation period of less than 900 seconds, the requirement of CDMA2000 phase synchronization under 10 us could be achieved for more than 40,000 seconds holdover time if we employ an OCXO (Oven Controlled Crystal Oscillator) clock. Second, in order to achieve the requirement of LTE-TDD under 1.5 us for more than 10,000 seconds holdover time, below 3 % estimation error and 500 seconds should be retained if a Rubidium clock is adopted.

• 한국항해항만학회지
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• 제33권1호
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• pp.35-41
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• 2009

워터젯이 탑재된 RIB(Rigid Inflatable Boat)형태의 무인수상선을 인한 경유점 추적 제어 알고리즘을 설계하였고, 성능 검증을 위해 실해역 시험을 수행하였다. 본 연구에서 사용된 RIB형 무인수상선의 경유점 추적제어를 위해서는 방향제어를 위해 버킷각을 제어하여야 한다. 우선, 육상 관제소에 미리 입력된 경유점들의 위경도 등의 위치정보들을 바탕으로, 목표 방향각을 실시간 계산한다. 그리고, 무인수상선에 탑재된 마그네틱 콤파스 등의 센서로부터 받은 선수각 및 선수각속도의 값과 PD 제어기법을 이용하여, 버킷각 명령을 실시간 계산한다. 본 연구에서는, 바람 등의 외력으로 인한 표류각을 보정하기 위해 일정속도 이상에서는 실침로(Course Of Ground, COG)를 사용하였다. 또한, 설계된 경유점 추적 제어 알고리즘을 검증하기 위해 부산 광안대교 근처 해역에서 육상관제소를 설치하고, 실선 시험을 수행하였다. 본 논문에서는, 설계된 무인 경유점 추적 제어 알고리즘의 시험결과를, 유인으로 제어한 결과 및 상용추적제어기로 제어한 결과들과 비교 분석하였다.

• 정보보호학회논문지
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• 제28권2호
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• pp.311-326
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• 2018

H.264/AVC-MPEG의 JM v10.2 코드 기반에서 QCIF ($176{\times}144$) 해상도를 가지는 News 샘플 영상을 사용하여 실험을 하였다. 암호화를 하게 될 관심영역(Region of Interest, ROI)이 H.264 표준의 움직임 예측 및 보상의 특성상 연속적으로 각 프레임마다 불필요하게 참조하여 드리프트를 발생시켰다. 드리프트를 완화하기 위해 암호화가 된 I픽처를 특정 주기로 재삽입하는 최신 관련연구의 방법은 추가 연산량 증가로 이어져 영상 전체의 비트레이트 오버헤드가 증가하는 요인이 된다. 따라서 움직임 예측 및 보상 단계에서 각 프레임마다 암호화가 될 관심영역에서의 Block과 Frame의 참조 탐색 범위를 제한하고, 암호화가 되지 않을 비관심영역에서의 참조 탐색 범위는 정상적인 인코딩 효율을 유지하기 위해 제한하지 않는다. 이와 같이 특정 참조 탐색 범위가 제한된 영상 인코딩을 한 후, 영상 속 개인정보 보호를 위해 얼굴과 같이 개인 식별이 가능한 관심영역에 대해 RC4 비트스트림 암호화 하는 방법을 제안한다. 그리고 동일한 환경의 조건에서 암호화되지 않은 원본 영상과 최신 관련연구 방법과 본 연구의 제안 방법을 각각 구현한 후, 실험 결과들을 비교 분석하였다. 최신 관련연구 방법과 다르게 제안방법을 통해 시간상 드리프트를 완화하면서, 제안방법이 적용된 영상 전체의 비트레이트 오버헤드가 원본 영상보다 2.35% 증가되고 최신 관련연구 방법보다 14.93% 감소되었다. 이와 같이 향상된 결과는 본 연구의 실험을 통해 입증하였다.