• 비파괴검사학회지
• /
• 제35권5호
• /
• pp.307-313
• /
• 2015

배관의 누설 검출은 주로 AE(acoustic emission) 센서와 같은 접촉식 센서가 이용되고 있다. 그러나 이러한 접촉식 센서는 고온이나 고방사능 지역에서 설치 및 운용의 어려움이 따른다. 이에 최근 원거리 감시 및 광역감시가 가능한 카메라를 이용한 누설 검출 방법에 대한 연구가 진행되어 왔다. 기존 카메라를 이용한 방법은 누설 검출을 위해 차영상 기법을 이용하고 있다. 그러나 이 방법은 누설뿐만 아니라 구조물의 진동이 누설로 검출되는 오류를 보이고 있다. 본 논문에서는 카메라를 이용한 누설 검출 방법에서 누설 검출 오류를 줄이기 위한 이동평균 차영상 및 히스토그램 분석법을 제안하였으며 실험을 통하여 성능을 평가하였다.

• Smart Structures and Systems
• /
• 제18권3호
• /
• pp.485-500
• /
• 2016

Stay cables in some cable-stayed bridges suffer large amplitude vibrations under the simultaneous occurrence of rain and wind. This phenomenon is called rain-wind-induced vibration (RWIV). The upper rivulet oscillating circumferentially on the inclined cable surface plays an important role in this phenomenon. However, its small size and high sensitivity to wind flow make measuring rivulet size and its movement challenging. Moreover, the distribution of the rivulet along the entire cable has not been measured. This paper applies the videogrammetric technique to measure the movement and geometry dimension of the upper rivulet along the entire cable during RWIV. A cable model is tested in an open-jet wind tunnel with artificial rain. RWIV is successfully reproduced. Only one digital video camera is employed and installed on the cable during the experiment. The camera records video clips of the upper rivulet and cable movements. The video clips are then transferred into a series of images, from which the positions of the cable and the upper rivulet at each time instant are identified by image processing. The thickness of the upper rivulet is also estimated. The oscillation amplitude, equilibrium position, and dominant frequency of the rivulet are presented. The relationship between cable and rivulet variations is also investigated. Results demonstrate that this non-contact, non-intrusive measurement method has good resolution and is cost effective.

• 한국구조물진단유지관리공학회 논문집
• /
• 제27권2호
• /
• pp.58-66
• /
• 2023

이 연구에서는 진동법을 이용하여 케이블 장력을 추정하고 비접촉 방식으로 케이블의 변위 응답을 측정하기 위한 센서로 영상기반시스템을 적용하였다. 영상기반시스템에서 카메라는 대상 구조물과 카메라의 시야를 고려한 위치에 설치된다. 그러나 설치하려는 위치의 이미지에는 대상 구조물과 차량 등의 다른 구조물이 포함될 수 있어 구조물의 변위 응답 측정에 필요한 기준점을 인식하기 어려울 수 있다. 영상기반시스템의 설치 위치로 인해 차량이 포함된 왜곡된 이미지는 이미지 해석에서 부정확한 결과를 나타내므로 두 이미지 사이의 유사성을 산정하여 차량이 포함된 이미지를 제거하였다. 제안된 방법을 이용한 사장교 케이블의 장력을 측정하는 방법의 타당성을 확인하기 위해 공용 중인 사장교에서 진동법을 적용하여 장력을 측정하였다.

• 한국항공우주학회지
• /
• 제43권5호
• /
• pp.472-478
• /
• 2015

본 논문에서는 소형 위성 카메라의 영상안정화를 위해 진동외란 보상 및 궤도상 광학정렬이 가능한 능동형 광학 보정장치의 설계에 대해 연구하였다. 능동형 광학 보정장치는 초점면부 보정장치와 부경 보정장치로 이루어져 있다. 초점면부 보정장치는 영상센서에 유입되는 진동 외란을 초점면부에서 직접 보상하는 장치이다. 또한 부경 보정장치는 초점면부 보정장치와 협력하여 궤도상에서 능동적으로 광학정렬을 수행할 수 있는 장치이다. 본 논문에서는 해상도 1 m급 소형 위성에 적용 가능한 능동형 광학 보정장치 설계를 위해 소형 고해상도 위성 카메라의 요구도를 분석하고, 진동 외란 보상과 궤도상 광학정렬이 능동적으로 가능하도록 초점면부 보정장치와 부경 보정장치의 요구도를 선정하였다. 선정된 요구도를 기준으로 본 연구에서 설계된 능동형 광학 보정장치는 초점면부에서 진동외란 보상 및 초점조절, 부경에서 틸트 및 디스페이싱 보상이 가능하므로 독립적으로 5축 제어가 가능한 시스템이다.

• Journal of Advanced Marine Engineering and Technology
• /
• 제38권10호
• /
• pp.1275-1280
• /
• 2014

In this study, the performance of a real-time micro telescopic monitoring system is evaluated, in which an artificial neural network is adopted for the diagnoses of vibratory bodies, such as solid piping system or machinery. The structural vibration was measured by a non-contact remote sensing method, in which images of a high-speed high-definition camera were used. The structural vibration data that can be obtained by the PIV (particle image velocimetry) technique were used for training the neural network. The structures of the neural network are dynamically changed and their performances are evaluated for the constructed diagnosis system. Optimized structures of the neural network are proposed for real-time diagnosis for the piping system. It was experimentally verified that the performances of the neural network used for real-time monitoring are influenced by the types of the vibration data, such as minimum, maximum and average values of the vibration data. It concludes that the time-mean values are most appropriate for monitoring the piping system.

• Journal of the Optical Society of Korea
• /
• 제12권3호
• /
• pp.126-130
• /
• 2008

We propose and experimentally demonstrate an effective method to reduce near-field speckle noise at the output of a 50 ${\mu}m$ graded index multimode fiber using a short cylindrical piezoelectric transducer(PZT) vibrating in the radial direction. The fiber was coiled as tightly as possible around the mandrel of the PZT and a periodic stretching effect was caused by the radial oscillations of the actuator. The output of the optical fiber using the He-Ne laser source was intensively observed by a CCD camera. By counting all the pixels corresponding to relative intensity graded into 256 levels in the selected area and by calculating standard deviation and mean value of the intensity, we could measure the speckle contrast and vibration effect quantitatively with reduction ratio of pixels and line profile of the illuminated region. It was clearly observed that the characteristics of the speckle pattern in the vibration-on state were significantly improved over that of the vibration-off state due to time-averaged smoothing.

• 센서학회지
• /
• 제27권5호
• /
• pp.300-305
• /
• 2018

The uncooled microbolometer thermal sensor for low cost and mass volume was designed to target the new infrared market that includes smart device, automotive, energy management, and so on. The microbolometer sensor features 80x60 pixels low-resolution format and enables the use of wafer-level vacuum packaging (WLVP) technology. Read-out IC (ROIC) implements infrared signal detection and offset correction for fixed pattern noise (FPN) using an internal digital to analog convertor (DAC) value control function. A reliable WLVP thermal sensor was obtained with the design of lid wafer, the formation of Au80%wtSn20% eutectic solder, outgassing control and wafer to wafer bonding condition. The measurement of thermal conductance enables us to inspect the internal atmosphere condition of WLVP microbolometer sensor. The difference between the measurement value and design one is $3.6{\times}10-9$ [W/K] which indicates that thermal loss is mainly on account of floating legs. The mean time to failure (MTTF) of a WLVP thermal sensor is estimated to be about 10.2 years with a confidence level of 95 %. Reliability tests such as high temperature/low temperature, bump, vibration, etc. were also conducted. Devices were found to work properly after accelerated stress tests. A thermal camera with visible camera was developed. The thermal camera is available for non-contact temperature measurement providing an image that merged the thermal image and the visible image.

• 제어로봇시스템학회논문지
• /
• 제13권5호
• /
• pp.499-506
• /
• 2007

The tiny camera module used in a modern cellular phone requires precise assembly processes. To meet the requirement of high resolution and functionality, the number of parts used in a camera module becomes larger and larger. As the market grows rapidly, an automatic camera phone assembly process is required. However, diverse production line and short life cycle make it difficult to build an affordable assembly line. To attack this problem, a flexible and expandable lens assembly system is proposed. To save the manufacturing line set-up time, modular concept is adopted. Also, each module is designed to have intelligence to simplify the set-up process. The assembly system is built up on the standard flat-form that includes a vibration free base, air and electric supplies, and electronic controllers, etc. Furthermore, the assembly cell has the capability of handling tiny, thin, or transparent parts which are very difficult to identify without machine vision.

• 항공우주시스템공학회지
• /
• 제10권1호
• /
• pp.86-94
• /
• 2016

In this paper, position control of focal plane compensation device using piezoelectric actuator is conducted. The forcal plane compensation device installed on earth observation satellite camera compensates micro-vibration from reaction wheels. In this study, four experimental models of the open-loop compensation device are derived using MATLAB system identification toolbox in the input range of 0~50Hz. Subsequently, the PID controller for each model is designed and the performance test of each controller is conducted through MATLAB/Simulink. According to frequency response analysis of the closed-loop compensation device system, the PID controller designed for 38~50Hz input range has enough tracking performance for the whole 0~50Hz input range. The maximum output error is about $1{\mu}m$ for the input range. The simulation results has been verified by the experimental method.

• 항공우주시스템공학회지
• /
• 제12권3호
• /
• pp.86-96
• /
• 2018

본 논문에서 제안한 캔위성은 2017년 캔위성 경연대회에 출전한 $HA+RC^2S$ CanSat (High Agility and Remote Control Camera System Can Satellite)이다. 주요임무는 수동진동감쇠기인 동흡진기를 사용하여 카메라를 회전시킨 직후에 발생하는 잔류진동을 감쇠하여 고품질의 영상획득이 가능한 고기동 안정화 카메라 시스템을 검증하는 것이다. 부가적으로는 지상국의 조이스틱을 사용하여 무선으로 제어되는 원격 제어 셀프카메라로 캔위성 자체의 이미지데이터를 획득하는 것이다. 본 논문에서는 임무 정의, 시스템 설계, 제작, 기능 및 성능시험, 최종 비행시험을 포함하는 $HA+RC^2S$ CanSat의 개발과정에 대해 서술하였다.