• 치과방사선
• /
• 제21권1호
• /
• pp.137-143
• /
• 1991

In the study of the focal trough of panoramic radiograph using Panoura Eight-S (the Yoshida company), a series of 63 X-ray films were taken with the 8-19 metal pins placed in the holes of the plastic model plate and evaluated by 4 observers. The author analized the focal trough defined by the sharpness criteria and calculated dimension of focal trough in the horizontal plane. The results were as follows; 1. Focal trough was not continued in the anterior region within a very high degree of sharpness. 2. With optional sharpness, the width of anterior and posterior focal trough was approximately l3㎜ and 60㎜ respectively. 3. The focal trough was narrow in the anterior region and was flared laterally with symmetry in posterior region. 4. Sharp image began to show at the position of 18㎜ posteriorly from the most anterior position of chin rest.

• 한국통신학회논문지
• /
• 제31권4C호
• /
• pp.400-406
• /
• 2006

3차원 정보 복원이나 형상 복원, 가상 물체 삽입 등의 과정을 수행하기 위해서는 영상 촬영에 사용된 카메라의 위치와 방향, 그리고 초점 거리 등의 변수가 필요하다. 본 논문에서는 이차원 영상간의 대응관계를 이용하여 카메라 내부 변수인 초점 거리를 추정하는 셀프 캘리브레이션(self-calibration) 과정에서 특징점의 위치가 초점 거리 추정에 미치는 영향을 분석하였다. 캘리브레이션에 사용하는 특징점과 주점과의 거리에 따라 초점 거리 추정 결과에 미치는 영향을 시뮬레이션을 통하여 검증하고, 이를 바탕으로 오차 민감도를 줄일 수 있는 특징점 선택 방법을 제안한다.

• Current Optics and Photonics
• /
• 제5권5호
• /
• pp.514-523
• /
• 2021

Methods for absolute depth estimation have received lots of interest, and most algorithms are concerned about how to minimize the difference between an input defocused image and an estimated defocused image. These approaches may increase the complexity of the algorithms to calculate the defocused image from the estimation of the focused image. In this paper, we present a new method to recover depth of scene based on a sharpness-assessment algorithm. The proposed algorithm estimates the depth of scene by calculating the sharpness of deconvolved images with a specific point-spread function (PSF). While most depth estimation studies evaluate depth of the scene only behind a focal plane, the proposed method evaluates a broad depth range both nearer and farther than the focal plane. This is accomplished using an asymmetric aperture, so the PSF at a position nearer than the focal plane is different from that at a position farther than the focal plane. From the image taken with a focal plane of 160 cm, the depth of object over the broad range from 60 to 350 cm is estimated at 10 cm resolution. With an asymmetric aperture, we demonstrate the feasibility of the sharpness-assessment algorithm to recover absolute depth of scene from a single defocused image.

• 한국태양에너지학회 논문집
• /
• 제22권3호
• /
• pp.31-37
• /
• 2002

This experimental study represents the results of an analysis on the characteristics of flux density distributions in the focal region of solar concentrator. The characteristics of flux density distributions are investigated to optimally design and position a cavity receiver. This deemed very useful to find and correct various errors associated with a dish concentrator. We estimated the flux density distribution on the target placed along with focal lengths from the dish vertex to experimentally determine the focal length. It is observed that the actual focal point exists when the focal length is 2.17 m. We also evaluated the position of flux centroid, and it was found that there were errors within 2 cm from the target center. The total integrated power of 2467 W was measured under focal flux distributions, which corresponds to the intercept rate of 85.8%. As a result of the percent power within radius, approximately 90% of the incident radiation is intercepted by about 0.06 m radius.

• 한국신재생에너지학회:학술대회논문집
• /
• 한국신재생에너지학회 2005년도 춘계학술대회
• /
• pp.422-426
• /
• 2005

This experimental study represents the results of an analysis on the characteristics of flux density distribution in the focal region of solar concentrator. The characteristics of flux density distributions are investigated to optimally design and position a cavity receiver. This was deemed very useful to find and correct various errors associated with a dish concentrator. We estimated the flux density distribution on the target placed along with focal lengths from the dish vertex to experimentally determine the focal length. It is observed that the actual focal point exists when the focal length is 2.17m. The total integrated power and percent power was 2467W and $85.8\%$, respectively, in the case of small dish, and also 2095W and $79\%$, respectively, in the case of KIERDISH II. As a result of the percent power within radius, approximately $90\%$ of the incident radiation is intercepted by about 0.06 m radius. The minimum radius of receiver in KIERDISH II is found to be 0.15m and approximately $90\%$ of the incident radiation is intercepted by receiver aperture.

• 대한인간공학회지
• /
• 제16권3호
• /
• pp.1-10
• /
• 1997

This paper is concerned with the development and evaluation of the camera calibration method for a real-time head tracking system. Tracking of head movements is important in the design of an eye-controlled human/computer interface and the area of virtual environment. We proposed a video-based head tracking system. A camera was mounted on the subject's head and it took the front view containing eight 3-dimensional reference points(passive retr0-reflecting markers) fixed at the known position(computer monitor). The reference points were captured by image processing board. These points were used to calculate the position (3-dimensional) and orientation of the camera. A suitable camera calibration method for providing accurate extrinsic camera parameters was proposed. The method has three steps. In the first step, the image center was calibrated using the method of varying focal length. In the second step, the focal length and the scale factor were calibrated from the Direct Linear Transformation (DLT) matrix obtained from the known position and orientation of the camera. In the third step, the position and orientation of the camera was calculated from the DLT matrix, using the calibrated intrinsic camera parameters. Experimental results showed that the average error of camera positions (3- dimensional) is about $0.53^{\circ}C$, the angular errors of camera orientations are less than $0.55^{\circ}C$and the data aquisition rate is about 10Hz. The results of this study can be applied to the tracking of head movements related to the eye-controlled human/computer interface and the virtual environment.

• 한국광학회지
• /
• 제15권3호
• /
• pp.248-253
• /
• 2004

광섬유 탐침의 끝 단에서 반사하는 광을 이용하는 근접장 주사 광간섭계를 제안하고 제안한 근접장 주사 광간섭계를 이용하여 초점의 위치와 집광 초점면에서의 파면을 분석하였다. 파면의 분석은 광섬유 탐침의 끝 단에서 반사된 빛과 시료표면에서 반사된 빛을 간섭시키고, 탐침의 끝 단을 λ/4씩 위상천이 시키면서 4장의 간섭무늬를 얻은 후, 위상천이 알고리즘을 통하여 광학 수차를 구하는 방법을 이용하였다. 실험 결과 근접 주사시의 초점의 위치를 파장의 3분의 1 이하로 제어할 수 있음을 알 수 있었으며, 제안한 근접장 주사 광간섭계를 이용하여 구한 집광 초점면에서의 파면 수차 값이 트와이만-그린 간섭계를 이용하여 구한 파면 수차값과 잘 일치함을 확인할 수 있었다.

• 한국레이저가공학회지
• /
• 제17권3호
• /
• pp.1-9
• /
• 2014

In this study, we analyzed fiber laser welding for the pure copper thin plates in a series of secondary lithium-ion batteries; and performed the experiment for the purpose of the preceding study to replace bolt joints method the with the laser welding method. We have changed the peak power of the laser from 5 to 6kW, the pulse duration by 4, 6, 8, and 10ms, the frequency by 10, 12, 16, and 25Hz, and the focal position by -3, 0, and +3. As a result, when the focal position is at +3, the peak power is 5kW, and the pulse duration and the Frequency are 4ms and 25Hz, respectively, we obtain 2.1 and 2.5 times better tensional strengths, respectively, than the highest values of tensional strengths obtained with the focal positions at 0 and -3.

• 설비공학논문집
• /
• 제14권11호
• /
• pp.907-913
• /
• 2002

An experimental study on energy density distributions produced by dish solar concentrating system was performed to optimally design and rightly position a cavity receiver. This deemed also very useful to find and correct various errors associated with a concentrator. It is observed that the actual focal length is 2.17 m with a maximum energy density of 1.89 MW/$m^2$. By evaluating the position of flux centroid, it was found that there are errors within 2 cm from the target center. As a result of the percent power within radius, approximately 90% of the incident radiation is intercepted by about 0.06 m radius. The area concentration ratio normalized to 800 W/$m^2$ insolation and 90% mirror reflectivity was 347 suns. The total integrated power of 2467 W was measured under focal flux distributions, which corresponds to the intercept rate of 85.8%.

• Journal of Welding and Joining
• /
• 제22권1호
• /
• pp.58-64
• /
• 2004

The control of the weld bead shape is important in laser welding of the small parts. The effects of laser welding parameters on the weld bead shape in the pulsed Nd:YAG laser welding of STS 304L material were investigated. Shielding gas type, flow rate, pumping voltage, pulse frequency, pulse width, focal position and overlap distance were selected as laser welding parameters. Experiments were designed and conducted using the Taguchi method which was a statistical experimental method. The weld bead width, penetration, area and aspect ratio were measured and analysed as the weld bead shape properties and the welding parameters were optimized to maximize the weld aspect ratio. Weld aspect ratio were greatly affected by the pulse width, pumping voltage and pulse frequency, and somewhat by the overlap distance, and little by the shielding gas type, flow rate and focal position. A confirmation experiment were conducted using the optimized welding parameters.