• International Journal of Precision Engineering and Manufacturing
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• 제8권4호
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• pp.22-26
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• 2007

We describe a new way of implementing absolute displacement measurements by exploiting the optical comb of a femtosecond pulse laser as a wavelength ruler, The optical comb is stabilized by locking both the repetition rate and the carrier offset frequency to an Rb clock of frequency standard. Multiwavelength interferometry is then performed using the quasi-monochromatic beams of well-defined generated wavelengths by tuning an external cavity laser diode consecutively to preselected light modes of the optical comb. This scheme of wavelength synthesizing allows the measurement of absolute distances with a high precision that is traceable to the definition of time. The achievable wavelength uncertainty is $1.9{\times}10^{-10}$, which allows the absolute heights of gauge blocks to be determined with an overall calibration uncertainty of 15 nm (k = 1). These results demonstrate a successful industrial application of an optical frequency synthesis employing a femtosecond laser, a technique that offers many possibilities for performing precision length metrology that is traceable to the well-defined international definition of time.

• 대한전자공학회논문지SD
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• 제41권2호
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• pp.27-32
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• 2004

Absolute optical angle 센서는 디지털 광학 장치의 핵심적인 부분이라고 말할 수 있으며, 이 장치의 목적은 Pseudorandom-code와 Geometry-code를 이 용하여 코드화된 원판(coded disk)의 상대적/절대적 변위 (Relative/Absolute angle position)를 해결하기 위함이다. 이 기술에서 디스크의 각 위치(Angular position)는 먼저 Pseudorandom-code에 의해 "Coarse" angle이 검출되어 결정되어지며, 그런 다음 Geometry-code의 Pixel 계산에 의해서 얻어지는 "Fine" angular position 데이터는, 7㎛의 Line image 센서를 사용 시, 시스템의 0.006°분해능 결과를 구할 수 있다. 제안된 기술은 비접촉 반사 특성, 시스템의 높은 분해능, 상대적으로 간단한 코트 패턴 그리고 센서의 고유한 디지털 성질을 갖는 등 많은 면에서 새로운 방식이다 더 나아가서 시스템은 두 개의 코드화된 원판에 적용하여 얻어진 절대 자의 변형(Absolute angular displacement)을 관찰하는 방식으로 쉽게 토크 센서로 변경할 수 있다. 제안된 센서의 디지털 광전 특성은 토크와 각을 동시에 측정함으로써 자동 차량 시스템에 사용 시 이상적인 시스템을 만든다. 본문에서는 코드화된 원판의 정확한 각 위치(Angular position)를 결정하기 위하여 Pseudo random-code와 Geometry-code를 활용한 기술을 제안하며, 아이디어의 실행 가능성을 구현하는 실험 결과를 제시하였다.

• 대한기계학회논문집B
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• 제29권7호
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• pp.784-794
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• 2005

In the very low specific speed range ($n_s=0.24$ < 0.25, non-dimensional), the efficiency of centrifugal pump designed by a conventional method is very low in common. Therefore, positive-displacement pumps have long been used widely. Recently, since the centrifugal pumps are becoming higher in rotational speed and smaller in size, there expects to develop a new centrifugal pump with a high performance to replace the positive-displacement pumps. The purpose of this study is to investigate the internal flow characteristics of a very low specific speed centrifugal pump and to examine the effect of internal flow pattern on pump performance. The results show that the theoretical head definition of semi-open impeller should be revised by the consideration of high slip factor in the semi-open impeller, and the leakage flow through the tip clearance results in a large effect on the impeller internal flow. Strong reverse flow at the outlet of semi-open impeller reduces the absolute tangential velocity considerably, and the decreased absolute tangential velocity increasese the slip factor with the reduction of theoretical head.

• 대한임베디드공학회논문지
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• 제18권3호
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• pp.117-124
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• 2023

In the machine vision inspection equipment, diameter measurement is important process in inspection of cylindrical object. However, machine vision inspection equipment requires complex algorithm processing such as camera distortion correction and perspective distortion correction, and the increase in processing time and cost required for precise diameter measurement. In this paper, we proposed the algorithm for diameter measurement of cylindrical object using the laser displacement sensor. In order to fit circle for given four input outer points, grid search algorithms using root-mean-square error and mean-absolute error are applied and compared. To solve the limitations of the grid search algorithm, we finally apply the singular-value-decomposition based circle fitting algorithm. In order to compare the performance of the algorithms, we generated the pseudo data of the outer points of the cylindrical object and applied each algorithm. As a result of the experiment, the grid search using root-mean-square error confirmed stable measurement results, but it was confirmed that real-time processing was difficult as the execution time was 10.8059 second. The execution time of mean-absolute error algorithm was greatly improved as 0.3639 second, but there was no weight according to the distance, so the result of algorithm is abnormal. On the other hand, the singular-value-decomposition method was not affected by the grid and could not only obtain precise detection results, but also confirmed a very good execution time of 0.6 millisecond.

• Earthquakes and Structures
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• 제5권4호
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• pp.439-459
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• 2013

Main objective of the present study is to determine the statistical properties and suitable probability distribution functions of spectral displacements from nonlinear static and nonlinear dynamic analysis within the frame work of Monte Carlo simulation for typical low rise and high rise RC framed buildings located in zone III and zone V and designed as per Indian seismic codes. Probabilistic analysis of spectral displacement is useful for strength assessment and loss estimation. To the author's knowledge, no study is reported in literature on comparison of spectral displacement including the uncertainties in capacity and demand in Indian context. In the present study, uncertainties in capacity of the building is modeled by choosing cross sectional dimensions of beams and columns, density and compressive strength of concrete, yield strength and elastic modulus of steel and, live load as random variables. Uncertainty in demand is modeled by choosing peak ground acceleration (PGA) as a random variable. Nonlinear static analysis (NSA) and nonlinear dynamic analysis (NDA) are carried out for typical low rise and high rise reinforced concrete framed buildings using IDARC 2D computer program with the random sample input parameters. Statistical properties are obtained for spectral displacements corresponding to performance point from NSA and maximum absolute roof displacement from NDA and suitable probability distribution functions viz., normal, Weibull, lognormal are examined for goodness-of-fit. From the hypothesis test for goodness-of-fit, lognormal function is found to be suitable to represent the statistical variation of spectral displacement obtained from NSA and NDA.

• Steel and Composite Structures
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• 제37권4호
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• pp.463-479
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• 2020

Currently, there are many lateral resisting systems utilized in resisting lateral loads being produced in an earthquake. Such systems can significantly reduce the roof's displacement when placed at an optimum location. Since in the design of tall buildings, the minimum distance between adjacent buildings is important. In this paper, the critical excitation method is used to determine the best location of the belt truss system while calculating the minimum required distance between two adjacent buildings. For this purpose, the belt truss system is placed at a specific story. Then the critical earthquakes are computed so that the considered constraints are satisfied, and the value of roof displacement is maximized. This procedure is repeated for all stories; i.e., for each, a critical acceleration is computed. From this set of computed roof displacement values, the story with the least displacement is selected as the best location for the belt truss system. Numerical studies demonstrate that absolute roof displacements induced through critical accelerations range between 5.36 to 1.95 times of the San Fernando earthquake for the first example and 7.67 to 1.22 times of the San Fernando earthquake for the second example. This method can also be used to determine the minimum required distance between two adjacent buildings to eliminate the pounding effects. For this purpose, this value is computed based on different standard codes and compared with the results of the critical excitation method to show the ability of the proposed method.

• International Journal of Ocean Engineering and Technology Speciallssue:Selected Papers
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• 제6권1호
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• pp.44-50
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• 2003

If the accelerometers are used in measuring the response, the absolute values of the velocity and displacement are not usually obtainable because their initial values are not accounted for in the integration of the acceleration response. A new dynamic response conversion algorithm of both the time domain and the frequency domain is proposed for the problem in estimating the displacement data by defining the transformed responses. In this algorithm, the displacement response can be obtained from the measured acceleration records by integration without requiring the knowledge of the initial velocity and displacement information. The applicability of the technique is tested by an example problem using the real bridge's superstructure under several cases of moving load. In the response conversion procedure of the frequency domain, the identified response according to the frequency can be estimated by changing over the limits of integration. If the reliability of the identified responses is ensured, it is expected that the proposed method for estimating the impact factor can be useful in the bridge's dynamic test. This method can be useful in those practical cases when the direct measurement of the displacement is difficult as in the dynamic studies of huge structure.

• 한국지진공학회논문집
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• 제21권5호
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• pp.215-226
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• 2017

In this paper, an experimental study was carried out for vibration control of cable bridges with structurally flexible characteristics. For the experiment on vibration control, a model bridge was constructed by reducing the Seohae Grand Bridge and the shear type MR damper was designed using the wind load response measured at Seohae Grand Bridge. The shear type MR damper was installed in the vertical direction at the middle span of the model bridge, and dynamic modeling was performed using the power model. The tests of the vibration control were carried out by non-control, passive on/off control and Lyapunov control method on model bridge with scaled wind load response. The performance of the vibration control was evaluated by calculating absolute maximum displacement, RMS displacement, absolute maximum acceleration, RMS acceleration, and size of applied power using the response (displacement, acceleration, etc.) from the model bridge. As a result, the power model was effective in simulating the nonlinear behavior of the MR damper, and the Lyapunov control method using the MR damper was able to control the vibration of the structure and reduce the size of the power supply.

• 한국측량학회지
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• 제6권1호
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• pp.35-41
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• 1988

지상사진에 의한 삼차원변형해석을 하는데 있어서 변위양계산의 정확도를 향상시키기 위해 반복경증률 상사변환법이 사용되었으며, 변위점검출에서는 Bayesian Inference가 적용되었고, 변위형태해석을 위해 변위방정식을 이용하는 방법을 제시하였다. 그 결과 변위양계산에서는 최소절대법($\Sigma$$\mid$d$\mid$⇒min)에 의한 경중률조건이 정확도를 향상시켰으며, 또한 Bayesian Inference을 적용하므로써 정확한 변위점검출을 할 수 있었다. 변위형태해석에서는 최적변위방정식을 이용하여 대상들의 전체 또는 부분적인 움직임을 해석할 수 있었다.

• 한국멀티미디어학회논문지
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• 제11권4호
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• pp.454-461
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• 2008

본 논문에서는 이동변위를 기반으로 하는 휴대기기의 새로운 입력 방법을 제안한다. 이를 위하여 휴대기기에 장착되어 있는 카메라를 이용하여 영상을 연속적으로 획득하고, 획득된 영상간의 변위를 실시간으로 계산함으로써 휴대기기의 이동 변위를 추정하였다. 제안하는 알고리즘은 획득된 영상간의 변위를 실시간으로 계산하기 위하여 계산량이 적은 SUSAN 코너 검출기를 사용하여 두 영상에서 특징점 들을 추출하였다. 다음으로 추출된 특징점 사이의 매칭작업을 수행하기 위하여 투 패스 알고리즘을 적용한 보로노이 평면을 생성하고, 두 영상의 거리 값인 SAD (Sum of absolute difference)를 계산함으로써 두 영상간의 변위를 계산하였다. 실험결과에서는 총 1500장의 영상을 이용하여 변위 추정알고리즘의 성능을 평가하였다. 그 결과 최대 90% 이상 매칭 성공률을 보였으며, 연산 속도는 5 ms 이내였다.