• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1996년도 한국자동제어학술회의논문집(국내학술편); 포항공과대학교, 포항; 24-26 Oct. 1996
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• pp.527-530
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• 1996

The Kalman filter has been used as a self-localization method for the mobile robot. To satisfy the assumptions inherent in the Kalman filter, we should calibrate the sensors of the robot before use of them. However, it is generally hard to find exact sensor parameters, and the parameters may change during the robot task as the environment varies. Thus we need to perform on-line sensor calibration, by which we can obtain more credible location of the mobile robot. In this paper, we present an on-line sensor calibration scheme which estimates the unknown sensor bias and the current position of the robot. To this end, first we find out the calibration errors of the sensor from redundant sensory data using the parity vector and recursive minimum variance estimation. Then we calculate the current position of the robot by weighted least square estimation without internal encoder data. The performance of the proposed method is evaluated through computer simulation.

• 융합신호처리학회논문지
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• 제13권1호
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• pp.32-38
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• 2012

센서 네트워크에서의 각 노드들은 지리적 위치에 기반을 둔 정보를 처리해야할 경우에 다양한 방법으로 자신의 위치를 알 수 있다. GPS를 이용한 위치 획득 방법은 전파의 가시성을 요구하므로 위치 정보를 획득할 수 없는 경우가 존재하고 비용이 많이들며, 전력소모가 많다. GPS 없이 센서 노드들의 위치를 알아내는 방법은 복잡한 수학적 알고리즘을 요구하며, 위치 추정의 정확도 측면에서 불리하다는 단점을 가지고 있다. AHLoS는 GPS를 이용한 위치 측정과 위치 추정 알고리즘을 모두 사용하는 혼합 방식이다. AHLoS에서 GPS 노드는 GPS로부터 수신한 자신의 위치를 자신과 인접한 GPS 기능이 없는 일반 노드로 방송한다. 일반 노드는 최소한 3개 이상의 이웃 노드의 위치 정보를 수신할 경우 삼각 측량 위치 계산 알고리즘의 반복 수행을 통해 자신의 위치를 계산할 수 있다. 그러나, 센서 네트워크에서 노드 이동성 네트워크 밀도 지리적 조건에 따라 노드가 3개 이상의 이웃 신호를 수신하지 못할 경우가 존재한다. 본 연구에서는 GPS 노드로부터 위치 정보를 3개 이상 직접 수신하기 어려운 저밀도 환경에서 각 센서 노드가 간접적으로 자신의 위치를 획득하는 방법을 제안한다.

• 한국컴퓨터정보학회논문지
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• 제22권9호
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• pp.33-40
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• 2017

In this paper, we propose a sink-location management and data-routing scheme to effectively support the mobile sink in solar-powered WSN. Battery-based wireless sensor networks (WSNs) have a limited lifetime due to their limited energy, but solar energy-based WSNs can be supplied with energy periodically and can operate forever. On the other hand, introduction of mobile sink in WSNs can solve some energy unbalance problem between sink-neighboring nodes and outer nodes which is one of the major challenges in WSNs. However, there is a problem that additional energy should be consumed to notify each sensor node of the location of the randomly moving mobile sink. In the proposed scheme, one of the nodes that harvests enough energy in each cluster are selected as the cluster head, and the location information of the mobile sink is shared only among the cluster heads, thereby reducing the location management overhead. In addition, the overhead for setting the routing path can be removed by transferring data in the opposite direction to the path where the sink-position information is transferred among the heads. Lastly, the access node is introduced to transmit data to the sink more reliably when the sink moves frequently.

• International Journal of Control, Automation, and Systems
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• 제2권4호
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• pp.485-493
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• 2004

Open-loop position estimation methods are commonly used in mobile robot applications. Their strength lies in the speed and simplicity with which an estimated position is determined. However, these methods can lead to inaccurate or unreliable estimates. Two position estimation methods are developed in this paper, one using a single optical flow sensor and a second using two optical sensors. The first method can accurately estimate position under ideal conditions and also when wheel slip perpendicular to the axis of the wheel occurs. The second method can accurately estimate position even when wheel slip parallel to the axis of the wheel occurs. Location of the sensors is investigated in order to minimize errors caused by inaccurate sensor readings. Finally, a method is implemented and tested using a potential field based navigation scheme. Estimates of position were found to be as accurate as dead-reckoning in ideal conditions and much more accurate in cases where wheel slip occurs.

• Journal of Electrical Engineering and Technology
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• 제11권4호
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• pp.889-897
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• 2016

This paper presents an improved approach for compensating rotor position signal displacement in brushless DC (BLDC) motors with misaligned hall-effect sensors. Typically, the hall-effect sensors in BLDC motors are located in each phase and positioned exactly 120 electrical degrees apart. However, limitations in mechanical tolerances make it difficult to place hall-effect sensors at the correct location. In this paper, a position error compensator to counteract the hall-effect sensor positioning error is proposed. The proposed position error compensator uses least squares error analysis to adjust the relative position error and back-EMF information to reduce the absolute offset error. The effectiveness of the proposed approach is verified through several experiments.

• 한국멀티미디어학회논문지
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• 제15권9호
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• pp.1112-1125
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• 2012

LBS(Location Based Service)를 위한 대표적인 수단으로 GPS가 많이 사용된다. 그러나 GPS는 야외 및 개방된 공간에서만 이용이 가능하다. 또한, 저전력을 기반으로 한 무선 센서네트워크에서의 활용은 비효율적이다. 본 논문에서는 실내 환경에서 위치 측위를 위하여 기존 시스템들과는 다른 접근 방법을 이용하여 위치를 측위 한다. 무선 센서네트워크에서 대표적으로 사용하는 IEEE 802.15.4를 기반으로 K-NN (K-Nearest Neighbor) 알고리즘에 중간값(Intermediate Value)을 적용하여, 더 세밀하게 위치를 측위 할 수 있는 시스템을 제안한다. K-NN의 경우 측정된 위치의 정교성은 셈플링의 개수에 비례한다. 그러나 센서네트워크에서 셈플링 개수를 무수히 늘리는 것은 비효율적이다. 본 논문에서는 셈플링값에 중간값을 적용하여 셈플링을 줄이는 알고리즘을 제안한다. 그리고 제안한 알고리즘을 구현하고 이를 실험하여 기존의 K-NN 기반의 위치 추정보다 약 두 배의 정밀도를 얻을 수 있음을 증명한다.

• 한국항행학회논문지
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• 제19권1호
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• pp.74-79
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• 2015

본 논문에서는 실내 위치 추적의 오차를 개선하기 위해 AP (access point)의 RSSI (received signal strength indication)가 미약한 지점에서 위치 정보의 정확성을 높일 수 있도록 스마트폰 센서를 이용하여 사용자의 보행정보를 검출하여 실내 위치 추적 오차를 개선할 수 있는 실내 위치 추적 시스템을 제안한다. 가속도 센서는 사용자의 보행 중 활동을 감지하고 이를 이용하여 보폭과 이동 거리를 검출할 수 있고, 방향 센서는 디지털 나침반으로써 활용되어 사용자의 이동 방향을 검출한다. 실험을 통해 센서를 이용한 보행 정보 검출 결과 걸음 수와 이동방향 검출에 대해 정확도를 높였다. 따라서 추가적인 장비와 비용 없이 센서와 RSSI를 활용하여 사용자의 이동 방향과 거리를 추정하고 기존 실내 위치 추적 시스템에서 오차를 보정할 수 있는 가능성을 확인하였다.

• Progress in Superconductivity
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• 제10권1호
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• pp.1-5
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• 2008

Magnetocardiography (MCG) is a non-contact, non-invasive, and harmless diagnostic tool to detect the abnormal electrical conductivities of the heart caused by the various coronary artery disease or cardiac muscular disease. The purpose of this study is to identify whether MCG signals and MCG parameter values vary depending on the location of sensor assembly. It will be an important reference for the standard measurement. Four healthy male subjects (33.3$\pm$6.3 years) participated in this study. Basal recording was made at 20 mm apart from the chest surface. All subjects were requested to take a regular breathe while MCG was taken. The gap between the chest surface and the bottom of the sensor assembly was 20, 40, 60, and 80 mm. Recording was made using 64 channel MCG system (Axial type, first order gradiometer) developed by Korea Research Institute of Standards and Science (KRISS). After resting for two minutes in a supine position on the bed in magnetically shielded room, MCG were recorded for 30 s. As the sensor location is getting away from the chest surface signal, the amplitude of R and T wave peak decreases to 70% (at 40 mm gap), 50% (at 60 mm), and 37% (at 80 mm) of the reference strength measured (y = $1.3903e^{-0.0169x}$, $R^2$ = 0.99; where y=amplitude remained after reduction, x=distance between chest surface and sensor location). The regression equations may be used as a good reference to calculate how much strength will be decreased by the distance. In MCG parameters, most values of parameters were decreased as the gap was increased. As an example, the current moment at T-wave peak reduced to 52% (at 40 mm gap), 33% (at 60 mm), and 19% (at 80 mm). However, the difference caused by the gap could be reduced by considering the distance when the MCG parameters were calculated. The study results can be used as a useful reference to design the baseline and the sensor location.

• Journal of Electrical Engineering and Technology
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• 제13권1호
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• pp.352-361
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• 2018

This paper proposes a sensing system of the Halbach array permanent magnet spherical motor(PMSM). The rotor position can be obtained by solving three rotation angles, which revolves around 3 reference axes of the stator. With the development of 3-D hall sensor, the position identification problem of the Halbach array PMSM based on rotor magnetic field is studied in this paper. A nonlinear and serious coupling relationship between the rotation angles and the measured magnetic flux density is established on the basis of the rotation transformation theory and the magnetic field model. In order to get rid of the influence on position detection caused by the harmonics of rotor magnetic field and the stator coil magnetic field, a sensor location combination scheme is proposed. In order to solve the nonlinear equation fast and accurately, a new position solution algorithm which combines the merits of gradient projection and particle swarm optimization(PSO) is presented. Then the rotation angles are obtained and the rotor position is identified. The validity of the sensing system is verified through the simulation.

• Smart Structures and Systems
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• 제26권6호
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• pp.721-733
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• 2020

The present study investigates the employing of piezoelectric patches in active control of a sandwich plate. Indeed, the active control and optimal patch distribution on this structure are presented together. A sandwich plate with honeycomb core and composite reinforced by carbon nanotubes in facesheet layers is considered so that the optimum position of actuator/sensor patches pair is guaranteed to suppress the vibration of sandwich structures. The sandwich panel consists of a search space which is a square of 200 × 200 mm with a numerous number of candidates for the optimum position. Also, different dimension of square and rectangular plates to obtain the optimal placement of piezoelectric actuator/senor patches pair is considered. Based on genetic algorithm and LQR, the optimum position of patches and fitness function is determined, respectively. The present study reveals that the efficiency and performance of LQR control is affected by the optimal placement of the actuator/sensor patches pair to a large extent. It is also shown that an intelligent selection of the parent, repeated genes filtering, and 80% crossover and 20% mutation would increase the convergence of the algorithm. It is noted that a fitness function is achieved by collection actuator/sensor patches pair cost functions in the same position (controllability). It is worth mentioning that the study of the optimal location of actuator/sensor patches pair is carried out for different boundary conditions of a sandwich plate such as simply supported and clamped boundary conditions.