• Journal of the Korean Solar Energy Society
• /
• v.29 no.6
• /
• pp.22-31
• /
• 2009

Canting is the optical alignment of mirror facets of heliostat such that the heliostat could focus the energy as a unit concentrator. Canting could improve the optical performance of heliostat and thus improves the efficiency of heliostat and ultimately improves the efficiency of the solar thermal power plant. This study discusses the effect of mirror canting, especially off-axis canting, used to compensate the sun tracking error caused by the heliostat geometrical errors. We first show that the canting could compensate the sun tracking error caused by the heliostat geometrical errors. Then we show that the proper canting time could exist, depending on the heliostat location. Finally we show how much the sun tracking performance could be improved by canting, by providing RMS sun tracking error. The limitation and caution of using canting to improve the sun tracking performance are also discussed.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 1991.04a
• /
• pp.59-67
• /
• 1991

공작기계의 정밀도는 가공물의 최종 치수 정밀도와 직접적으로 연계되는 공작기계의 전체적 성능 평가를 위한 주요인자 중의 하나이다. 공작기계 위치 결정 정밀도에가장 큰 영항을 주는 인자로서는 이송계의강성, Back lash, 안내면의 습동저항 그리고 이송 계의 자세변화등이 해당된다. 본 연구에서는 이송나사로구동되는 CNC 원통 연삭기의 숫돌대(Wheel Head)축 이송 구동계의 오차발생 요인에 대해 실험적인 검토를 수행하였다. 이를 위하여 이송 구동계의 정강성에따른 영향과 이송 안내면의 각운동에 의한 위치정밀도 영향 및 위치 검출 장치의 종류에 따른 위치오차의 재현성(Repeatatility)의 유무를 레이 저 간섭계를 이용한 정밀 측정을 통하여 비교 검토함에 의해 이송 오차를 최소화 시킬 수 있는 CNC 공작기계이송 구동축 설계의 기본 방향을 마련하는데 역점을 두고 연구를 수행하게 되었다.

• Proceedings of the KIPE Conference
• /
• 2012.07a
• /
• pp.75-76
• /
• 2012

본 논문에서는 고속 운전을 위하여 IPMSM(Interior Permanent Magnet Synchronous Motor)의 약계자 운전을 제시한다. IPMSM 운전을 위한 약계자 제어기는 SMO(Sliding Mode Observer)를 통한 추정 속도와 실제 전동기의 속도를 비교하여 나타나는 오차값을 피드백 받아서 이용한다. 기본적으로 속도 오차가 없는 상황에서는 MTPA(Maximum Torque Per Amp.)에서 동작 시키고 속도 오차가 증가하면 이 오차에 대해 d축 전류를 음의 방향으로 증가시켜 약계자 제어를 한다. 본 논문에서는 제시한 약계자 운전으로 IPMSM에 적용시험을 한다. 그리고 시험결과를 분석하여 본 논문의 타당성을 입증한다.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.23 no.2
• /
• pp.258-261
• /
• 2012

Helicopter-borne FMCW radar altimeter obtains the altitude information using the beat frequency between the transmitted and reflected signal from the nadir direction. However, the altitude error may exist when the strong echoes are received from the large RCS at the off-nadir direction because of the wide beamwidth of the altimeter antenna. In this paper, in order to investigate the effect of the altitude error due to the large RCS around the off-nadir direction, the reflected signals were measured by using the corner reflectors displaced on the several reference ground positions, and the acquired signals were analyzed and compared in the spectral domain. The analysis results can be used for the improvement of the altitude accuracy in the radar altimeter.

• The Journal of the Acoustical Society of Korea
• /
• v.10 no.1
• /
• pp.30-36
• /
• 1991

Since the Complex Young's Modulus of acoustic materials is a function of frequency under a static load, a cylindrical specimen modelled by rod-like one with losses is used to determine the dynamic characteristics of materials. The specimen is excited into longitudinal vibration at its one end by shaker and at the other end, loaded by a mass corresponding to the desired static load and thus the transfer function of specimen is measured. This transfer function method is analyzed theoretically and experimentally over a frequency range of 50 Hz to 20 KHz. The analysis includes the measurability of the transfer function, the frequency range of the method and lateral motion effect.

• Journal of the Korea Computer Graphics Society
• /
• v.3 no.2
• /
• pp.35-43
• /
• 1997

In monitor-based AR(Augmented Reality) systems, it is required to know the position and direction of a camera in order to combine real images from a camera with virtual images exactly_ Because a tracker is parted from a camera, however, there is a registration error caused by the inconsistency of a tracker with a camera. In this paper, we describe the error correction method using genetic algorithm. This method looks for the position and direction of a camera using genetic algorithm and solves the error correction matrix of it. And then it is registered of the real images and the revised virtual image. It has an effect on the error correction caused by the misalignment of a tracker with a camera in complex AR systems.

• Journal of the Korean Society of Marine Environment & Safety
• /
• v.27 no.5
• /
• pp.557-565
• /
• 2021

Path-following control is considered as one of the most fundamental skills to realize autonomous navigation of marine vessels in the ocean. This study addresses with the path-following control for a ship in which there are environmental disturbances in the directions of the surge, sway, and yaw motions. The guiding principle and back-stepping method was utilized to solve the ship's tracking problem on the reference path generated by a virtual ship. For path-following control, error dynamics is one of the most important skills, and it extends to the research fields of automatic collision avoidance and automatic berthing control. The algorithms for the guiding principles and error variables have been verified by numerical simulation. As a result, most error variables converged to zero values with the controller except for the yaw angle error. One of the most interesting results is that the tracking errors of path-following control between two ships are smaller than the existing safe passing distances considering interaction forces from near passing ships. Moreover, a trade-off between tracking performance and the ship's safety should be considered for determining the proper control parameters to prevent the destructive failure of actuators such as propellers, fins, and rudders during the path-following of marine vessels.

• Journal of the Korean Society of Radiology
• /
• v.15 no.6
• /
• pp.861-867
• /
• 2021

Since SBRT takes up to 1 hour from 30 minutes to treatment fraction once or three to five times, there is a possibility of setup error during treatment. To reduce these set-up errors and give accurate doses, we intend to evaluate the usefulness of pre-treatment and post-treatment error values by imaging CBCT again to determine postural movement due to pre-treatment coordinate values using pre-treatment CBCT. On average, the range of systematic errors was 0.032 to 0.17 on the X and Y,Z axes, confirming that there was very little change in movement even after treatment. Tumor centripetal changes (±SD) due to respiratory tuning were 0.11 (±0.12) cm, 0.27 (±0.15) cm, and 0.21 cm (±0.31 cm) in the X, Y and Z directions. The tumor edges ±SD were 0.21 (±0.18) cm, 0.30 (±0.23) cm, and 0.19 cm (±0.26) cm in the X, Y and Z directions. The (±SD) of tumor-corrected displacements were 0.03 (±0.16) cm, 0.05 (±0.26) cm, and 0.02 (±0.23) cm in RL, AP, and SI directions, respectively. The range of the 3D vector value was 0.11 to 0-.18 cm on average when comparing pre-treatment and CBCT, and it was confirmed that the corrected set-up error was within 0.3 cm. Therefore, it was confirmed that there were some changes in values depending on some older patients, condition on the day of treatment, and body type, but they were within the significance range.

• The Journal of Korean Society for Radiation Therapy
• /
• v.22 no.1
• /
• pp.11-18
• /
• 2010

Purpose: In every time radiation therapy set up errors occur because internal anatomical organs move due to breathing and change of patient's position. These errors may affect the change of dose distribution between target area and normal structure. This study investigates the usefulness of body-fix in clinical treatment. Materials and Methods: Among 55~60 aged male patients who has hepatocellular carcinoma in area of liver's couinaud classification, we chose 10 patients and divided two groups by using body-fix or not. When applying body-fix, we maintained a vacuum of 80 mbar pressure by using vacuum pump (Medical intelligence, Germany). Patients had free breathing with supine position. After working to fuse and consist MV-CT (megavoltage computed tomography) with KV-CT (kilovoltage computed tomography) obtained by 5 times treatments, we compared and analyzed set up errors occurred to (Right to Left, RL) of X axis, (Anterioposterio, AP) of Z axis, (Cranicoudal, CC) of Y axis. Results: Average Set up errors through image fusion showed that group A moved $0.3{\pm}1.1\;mm$ (Cranicoudal, CC), $-1.1{\pm}0.7\;mm$ (Right to Left, RL), $-0.2{\pm}0.7\;mm$ (Anterioposterio, AP) and group B moved $0.62{\pm}1.94\;mm$ (Cranicoudal, CC), $-3.62{\pm}1.5\;mm$ (Right to Left, RL), $-0.22{\pm}1.2\;mm$ (Anterioposterio, AP). Deviations of X, Y and Z axis directions by applying body-fix indicated that maximum X axis was 5.5 mm, Y axis was 19.8 mm and Z axis was 3.2 mm. In relation to analysis of error directions, consistency doesn't exist for every patient but by using body-fix showed that the result of stable aspect in spite of changes of everyday's patient position and breathing. Conclusion: Using body-fix for liver cancer patient is considered effectively for tomotherapy. Because deviations between group A and B exist but they were stable and regular.

• Korean Journal of Optics and Photonics
• /
• v.28 no.6
• /
• pp.290-294
• /
• 2017

The Cassegrain telescope consists of a primary concave mirror and a secondary convex mirror. In the case of a secondary mirror, it is more difficult to test wavefront error than for a primary mirror, because it reflects the entire testing beam, as it is convex in shape. In this paper we tested the wavefront error of a complex aspheric convex secondary mirror by using the Simpson-Oland-Meckel Hindle test. To separate the systematic errors, such as fabrication error and alignment error of a meniscus lens, we adopted the QN absolute test (pixel-based absolute test using the quasi-Newton method) as well. Finally, we compared the measured result with that of an ASI (Aspheric Stitching Interferometer) made by the QED company, which resulted in an rms difference of only 2.5 nm, showing a similar shape of astigmatism aberration.