• 한국멀티미디어학회논문지
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• 제24권3호
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• pp.355-372
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• 2021

Recently, high-performance HMDs (Head-Mounted Display) are becoming wireless due to the growth of virtual reality technology. Accordingly, environmental constraints on the hardware usage are reduced, enabling multiple users to experience virtual reality within a single space simultaneously. Existing multi-user virtual reality platforms use the user's location tracking and motion sensing technology based on vision sensors and active markers. However, there is a decrease in immersion due to the problem of overlapping markers or frequent matching errors due to the reflected light. Goal of this study is to develop a multi-user virtual reality moving platform in a single space that can resolve sensing errors and user immersion decrease. In order to achieve this goal hybrid sensing technology was developed, which is the convergence of vision sensor technology for position tracking, IMU (Inertial Measurement Unit) sensor motion capture technology and gesture recognition technology based on smart gloves. In addition, integrated safety operation system was developed which does not decrease the immersion but ensures the safety of the users and supports multimodal feedback. A 6 m×6 m×2.4 m test bed was configured to verify the effectiveness of the multi-user virtual reality moving platform for four users.

• 한국음향학회지
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• 제40권6호
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• pp.546-554
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• 2021

수중 탐지를 위한 합성개구소나(Synthetic Aperture Sonar, SAS) 신호처리에서는 탑재플랫폼이 직선경로를 따라 주행한다고 가정한다. 그러나 실제로는 플랫폼의 복잡한 운동에 따른 궤적 교란으로 인해 SAS 영상에 번짐과 같은 왜곡이 발생한다. 본 연구에서는 예인형 SAS 개발을 위해 궤적 교란에 의한 SAS 영상 왜곡을 개선하기 위한 방법으로서, Redundant Phase Center (RPC)을 이용한 예인체 운동 추정 및 영상 보정, 그리고 자동 초점 기법인 Phase Gradient Autofocus (PGA) 기법에 대해 검토하였다. 그리고 시뮬레이션을 통해, sway로 인해 왜곡된 SAS 영상에 이 기법들을 적용하고 그 성능 및 유효성에 대해 살펴보았다.

• Smart Structures and Systems
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• 제31권4호
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• pp.409-419
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• 2023

Structural integrity can be accessed from dynamic deformations of structures. Moreover, dynamic deformations can be acquired from non-contact sensors such as video cameras. Kanade-Lucas-Tomasi (KLT) algorithm is one of the commonly used methods for motion tracking. However, averaging throughout the extracted features would induce bias in the measurement. In addition, pixel-wise measurements can be converted to physical units through camera intrinsic. Still, the depth information is unreachable without prior knowledge of the space information. The assigned homogeneous coordinates would then mismatch manually selected feature points, resulting in measurement errors during coordinate transformation. In this study, a two-stage optimization method for video-based measurements is proposed. The manually selected feature points are first optimized by minimizing the errors compared with the homogeneous coordinate. Then, the optimized points are utilized for the KLT algorithm to extract displacements through inverse projection. Two additional criteria are employed to eliminate outliers from KLT, resulting in more reliable displacement responses. The second-stage optimization subsequently fine-tunes the geometry of the selected coordinates. The optimization process also considers the number of interpolation points at different depths of an image to reduce the effect of out-of-plane motions. As a result, the proposed method is numerically investigated by using a truss bridge as a physics-based graphic model (PBGM) to extract high-accuracy displacements from recorded videos under various capturing angles and structural conditions.

• 한국전자파학회논문지
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• 제28권7호
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• pp.580-583
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• 2017

항공기 탑재형 SAR에서 요동보상 후 남아있는 잔여 오차 및 공간 가변적 오차 등으로 인해 품질이 저하된 SAR 영상을 보상하기 위한 분할처리 기반 자동초점 기법을 제시한다. Spotlight SAR는 공간 분할하고, Stripmap SAR는 시간 분할한 뒤, 분할된 데이터에 대해 영상을 생성한 후, 추정된 오차의 적합성 분석과정이 포함된 구역 자동초점 기법(Autofocus)를 수행한다. 또한 분할된 영상에서 위상오차 추정이 되지 않아 보상이 되지 않는 경우에는 인접한 분할 영상의 위상오차에 가중치를 부여하여 보상하는 과정을 통해 전체 영상의 화질을 향상시키는 방법을 제시한다.

• 한국정밀공학회지
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• 제22권11호
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• pp.111-117
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• 2005

The vibration problems associated with gear coupled rotors have been the focus of much engineering work. These systems are complex and difficult to analyze in that they have the problems associated with conventional rotors plus those additional problems associated with the gear couplings. This paper examines the problems peculiar to the gear mesh. Because of the meshing action of gears, the elasticity of the gear teeth introduces time-varying stiffness coefficients into the governing equations of motion. This means that system response must be thought of in terms of Mathieu-type equations, where multiple-frequency response occur due to the periodic coefficients. The meshing action of the gears also couples the lateral and torsional gear motions. Gear errors, such as tooth profile and spacing errors, produce forces and torque that excite the system at multiple frequencies, some of which are much higher than shaft rotational speed. To investigate how to the time-varying stiffness in the gear teeth and the gear errors act one the dynamic response of the gear coupled rotors, a three-dimensional dynamic model with lateral-tortional oscillation is developed. The harmonic balance technique is employed to solve this mathieu-type problem.

• 한국컴퓨터정보학회논문지
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• 제7권2호
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• pp.95-100
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• 2002

피드백 채널을 이용한 디코더는 인코더로 전송에러에 의한 오염된 매크로 블록들의 주소를 알려준다. NACK 메시지의 수신으로 인코더는 전송에러가 발생된 프레임의 GOB와 MB를 기준으로 forward dependency를 적용으로 확산된 에러전파영역을 지닌 다음순서의 프레임을 만들어낸다. 이 프레임으로 현재 인코딩 하려는 프레임의 각 MB안에 4-corner에 존재하는 픽셀들에 대한 backward dependency를 적용함으로써 오염된 MB을 찾아낼 수가 있다. 이들 오염된 MB들에 대한 INTRA코딩을 적용함으로써 에러확산을 완전히 중단시킬 수 있다. 이와 같이 빠른 알고리즘의 적용으로 보다 적은 연산량과 보다 적은 양의 메모리 요구를 얻을 수 있다 또한 이러한 장점은 실시간 비디오 전송에 특히 적합하다.

• 대한기계학회논문집
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• 제17권12호
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• pp.3115-3123
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• 1993

This paper presents a real-time correction method of the movemont errors of a translatory precision machine axis. This method is a null-balances technique in which two plane mirrors are used to generate an interferometric fringe pattern utilizing the optical principles of TwymanGreen interferometry. One mirror is fixed on a reference frame, while the other is placed on the machine axis being supported by three piezoelectric actuators. From the fringe pattern, one translatory and two rotational error components of the machine axis are simultaneously detected by using CCD camera vision and image processing techniques. These errors are then independently suppressed by activating the peizoelectric actuators by real-time feedback control while the machine axis is moving. Experimental results demonstrate that a machine axis can be controlled with movement errors less than 10 nm in vertical straightness, 0.1 arcsec in pitch, and 0.06 arcsec in roll for 50mm travel by adopting the real-time correction method.

• Journal of Mechanical Science and Technology
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• 제19권6호
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• pp.1253-1267
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• 2005

Misalignment can be an important problem in the integration of GPS/INS. Observability analysis of the alignment errors in the integration of low-grade inertial sensors and multi-antenna GPS is presented in this paper. A control-theoretic approach is adopted to study the observability of time-varying error dynamics models. The relationship between vehicle motions and the observability of the errors in the lever arm and relative attitude between GPS antenna array and IMU is given. It is shown that alignment errors can be made observable through maneuvering. The change of acceleration makes the components of the relative attitude error that are orthogonal to the direction of the acceleration change observable. The change of angular velocity makes the components of the lever arm error that are orthogonal to the direction of the angular velocity observable. The motion of constant angular velocity has no influence on the estimation of the lever arm.

• ETRI Journal
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• 제40권2호
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• pp.266-274
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• 2018

In error-prone wireless environments, it is difficult to realize video coding systems that are robust to various types of data loss. In this paper, a novel motion-vector refinement approach is presented for video error concealment. A traditional boundary-matching approach is exploited to reduce blocky effects along the block boundary. More specifically, a downhill simplex approach is combined with a boundary-matching approach to fine-tune the motion vectors, reducing the blocky effects along the prediction unit block boundary, and minimizing the computational cost. Extensive simulations are performed, and the results obtained verify the robustness and effectiveness of the proposed approach.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2004년도 ICCAS
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• pp.82-86
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• 2004

A fuzzy rule-based hand-motion estimation algorithm is proposed for a 6 dimensional spatial tracker in which low cost accelerometers and gyros are employed. To be specific, beginning and stopping of hand motions needs to be accurately detected to initiate and terminate integration process to get position and pose of the hand from accelerometer and gyro signals, since errors due to noise and/or hand-shaking motions accumulated by integration processes. Fuzzy rules of yes or no of hand-motion-detection are here proposed for rules of accelerometer signals, and sum of derivatives of accelerometer and gyro signals. Several experimental results and shown to validate our proposed algorithms.