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

• Transactions of the Korean Society of Automotive Engineers
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• v.5 no.3
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• pp.35-46
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• 1997

In order to satisfy customer's requirements of ride comfort and high performance, it is necessary for designers to fully understand vehicle aerodynamics and wind noise of newly produced cars because characteristics of flow and wind noise are heavily dependent on each other. In this study numerical and experimental study have been carried out to analyse the effect of flow characteristics at around of rear view mirror on wind noise and soiling on the front S/W. As a result, it's found that the spiral flow mear the front pillar is weakened and spreaded because rear view mirror obstructs the flow. It is also shown that there is abrupt change of gradient of separa- tion line, separation area, intensity of spiral flow and turbulent kinetic energy with varying shape of neck and housing of rear view mirror.

• Advanced Composite Materials
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• v.16 no.3
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• pp.245-258
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• 2007

The single-modal Weibull model has been assessed on Tyranno ZMI Si-Zr-C-O fiber if a set of shape and scale parameters accurately reproduced the effect of the size of the diameter on strength. The tensile data of a single fiber have been divided into two expedient groups as 'small diameter' group and 'large diameter' group in deriving the parameters, which should be consistent if the Weibull model accurately reproduced the size effect. However, the derived Weibull parameters were inconsistent between the two groups. Thereby the authors have concluded that the parameters of the single-modal Weibull model are dependent on the fiber diameter, so that the model is inadequate to reproduce the strength size effect. On the other hand, Weibull parameters were found consistent between the two groups by excluding the data of 'large mirror zone' sample, which was defined as the sample around 10% mirror zone area of the fracture surface. What is more, the exclusion reduced the strength variance more drastically in the 'large diameter' group than in the 'small diameter' group, even though the 'large mirror zone' samples were found identical in the percentage between the two groups. The authors therefore conclude that diameter limitation to the 'small diameter' group level can lead to drastically less distributed strength values than the estimated strength through the Weibull scaling on the present Tyranno ZMI Si-Zr-C-O fiber.

• Korean Journal of Optics and Photonics
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• v.26 no.3
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• pp.139-146
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• 2015

The effects of a dielectric multilayer mirror on the efficiency of organic light-emitting diodes (OLEDs) were investigated by using optical simulation. Adoption of a dielectric mirror consisting of alternating SiN and $SiO_2$ layers narrowed the emission spectrum due to the microcavity effect, and increased the outcoupling efficiency by a few percent. The layer thicknesses of the dielectric mirror were adjusted to change the wavelength of the resonance mode, which may be used to increase the color purity.

• 제어로봇시스템학회:학술대회논문집
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• 2005.06a
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• pp.1994-1998
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• 2005

Characteristic analysis of the depth measurement system with a laser, a camera and a rotating mirror has been done and the parameter calibration technique for it has been proposed. In the proposed depth measurement system, the laser beam is reflected to the object by the rotating mirror and again the position of the laser beam is observed through the same mirror by the camera. The depth of the object pointed by the laser beam is computed depending on the pixel position on the CCD. There involved several number of internal and external parameters such as inter-pixel distance, focal length, position and orientation of the system components in the depth measurement error. In this paper, it is shown through the error sensitivity analysis of the parameters that the most important parameters in the sense of error sources are the angle of the laser beam and the inter pixel distance. The calibration techniques to minimize the effect of such major parameters are proposed.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.13 no.5
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• pp.403-411
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• 2020

Since the analog circuit of the beta ray sensor circuit for the true random number generator and the power and ground line used in the comparator circuit are shared with each other, the power generated by the digital switching of the comparator circuit and the voltage drop at the ground line was the cause of the decreasein the output signal voltage drop at the analog circuit including CSA (Charge Sensitive Amplifier). Therefore, in this paper, the output signal voltage of the analog circuit including the CSAcircuit is reduced by separating the power and ground line used in the comparator circuit, which is the source of digital switching noise, from the power and ground line of the analog circuit. In addition, in the voltage-to-voltage converter circuit that converts VREF (=1.195V) voltage to VREF_VCOM and VREF_VTHR voltage, there was a problem that the VREF_VCOM and VREF_VTHR voltages decrease because the driving current flowing through each current mirror varies due to channel length modulation effect at a high voltage VDD of 5.5V when the drain voltage of the PMOS current mirror is different when driving the IREF through the PMOS current mirror. Therefore, in this paper, since the PMOS diode is added to the PMOS current mirror of the voltage-to-voltage converter circuit, the voltages of VREF_VCOM and VREF_VTHR do not go down at a high voltage of 5.5V.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.05a
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• pp.859-865
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• 2007

This paper presents a method to analyze the unbalance response of a high speed polygon mirror scanner motor supported by sintered bearing and flexible supporting structures by using the finite element method and the mode superposition method. The appropriate finite element equations for polygon mirror are described by rotating annular sector element using Kirchhoff plate theory and von Karman non-linear strain, and its rigid body motion is also considered. The rotating components except for the polygon mirror are modeled by Timoshenko beam element including the gyroscopic effect. The flexible supporting structures are modeled by using a 4-node tetrahedron element and 4-node shell element with rotational degrees of freedom. Finite element equations of each component of the polygon mirror scanner motor and the flexible supporting structures are consistently derived by satisfying the geometric compatibility in the internal boundary between each component. The rigid link constraints are also imposed at the interface area between sleeve and sintered bearing to describe the physical motion at this interface. A global matrix equation obtained by assembling the finite element equations of each substructure is transformed to a state-space matrix-vector equation, and both damped natural frequencies and modal damping ratios are calculated by solving the associated eigenvalue problem by using the restarted Arnoldi iteration method. Unbalance responses in time and frequency domain are performed by superposing the eigenvalues and eigenvectors from the free vibration analysis. The validity of the proposed method is verified by comparing the simulated unbalance response with the experimental results. This research also shows that the flexibility of supporting structures plays an important role in determining the unbalance response of the polygon mirror scanner motor.

• Korean Journal of Optics and Photonics
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• v.12 no.2
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• pp.77-82
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• 2001

Error characteristics of a mirror loss measurement system using an exponential decay method were studied, with the two samples having about 200-ppm-loss and 30-ppm-loss, respectively. In order to minimize the decay signal deviation from an exponential curve due to cavity length fluctuation, a data average method was tried. The data average method significantly improved the exponential curve fitting error of the decay signal, so that for a 6 decay signal data average the loss measurement error was reduced by about 2.4 times for the 200-ppm-loss mirror and 1.3 times for the 30-ppm-loss mirror compared with a single shot measurement. Day-to-day mirror loss repeatability error for the two samples was investigated. The repeatability error was measured to be about 5% for the 200-ppm-loss mirror and about 26.4% for the 30-ppm-loss mirror. Low decay signal average effect and high repeatability error in the low loss mirror measurement were explained with non-uniform spatial loss distribution of the sample and contamination from the environment, in addition to the error sources of the mirror loss measurement system itself. The influence of cavity length fluctuation and cavity length measurement error on the mirror loss measurement system performance was theoretically calculated. It confirmed that the requirement for the cavity length parameters was not so strict in the mirror loss measurement system of several ppm resolution. ution.

• Journal of the Korean Solar Energy Society
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• v.29 no.3
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• pp.1-11
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• 2009

Heliostat sun tracking accuracy could be the most important requirement in solar thermal power plant, since it determines the overall efficiency of power plant. This study presents the effect of geometrical errors on the heliostat sun tracking performance. The geometrical errors considered here are the mirror canting error, encoder reference error, heliostat position error. pivot offset and tilt error, gear backlash and mass unbalanced effect error. We first investigate the effect of each individual geometrical error on the sun tracking accuracy. Then, the sun tracking error caused by the combination of individual geometrical error is computed and analyzed. The results obtained using the solar ray tracing technique shows that the sun tracking error due to the geometrical error is varying almost randomly. It also shows that the mirror canting error is the most significant error source, while the encoder reference error and gear backlash are second and the third dominant source of errors.

• Journal of the Korean Vacuum Society
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• v.10 no.2
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• pp.145-154
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• 2001

A new type of modular mirror manipulator with independent adjustability was developed for the EPU6 beamline under construction at the Pohang Accelerator Laboratory. The mirror manipulator was designed so that the angular displacements of roll and pitch rotations do not introduce translational displacements and are independent with each other by positioning the mirror center to the center of a newly devised spherical joint. Manipulating its roll and pitch micrometers, the rotation angles of a dummy mirror were measured at an accuracy of 5 $\mu$rad using a gravity-referenced inclinometer. While the designed angular resolution was 3.937 $\mu$rad/$\mu\textrm{m}$, measured angular resolutions were 3.94 $\mu$rad/$\mu\textrm{m}$ for roll rotation and 3.85 $\mu$rad/$\mu\textrm{m}$ for pitch rotation. The effect of roll rotation on pitch angles was measured to be -3.18% and the effect of pitch rotation on roll angles was measured to be -5.21%. As the mirror manipulator was designed with emphases on independent adjustability and standardization, it results in eases of manufacturing, installation and adjustment as well as reductions of development period and design cost of mirror manipulators for various types of mirrors.