• Transactions of the Korean Society of Machine Tool Engineers
• /
• v.12 no.6
• /
• pp.1-7
• /
• 2003

The experimental research was conducted to find an end mill with an ideal helix angle, which has a superior anti-vibration effect and a low machining tolerance. A conventional endmill which all low blades are $30^{\circ}$ helix angles and a different helix angle endmill which the opposite two blades are $30^{\circ}$ and the other opposites are different helix angles were studied. The cutting farce, machining tolerance and surface roughness were obtained. The AE signals appeared to have low values in up-milling rather than in down-milling. These are also appeared to have low values at low spindle revolutions rates. The cutting force values of Fxy and Fxyz were found to be increased according to the value of helix angle. In up-milling, it was difficult to find a definite tendency in machining tolerance, but in down-milling machining tolerance of the different helix angle end mill was found to be lower than that of the convention end mill. There is a definite tendency that the surface roughness gets better as the RPM increases. In down-milling, Type A($25^{\circ}$＋$30^{\circ}$) appeared to bring the most satisfactory result.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
• /
• 2003.04a
• /
• pp.196-201
• /
• 2003

The experimental research was conducted to find an end mill with an ideal helix angle, which has a superior anti-vibration effect and a low machining-tolerance. A conventional endmill which all four blades are $30^\circ$ helix angles and a different helix angle endmill which the opposite two blades are $30^\circ$ and the other opposites are different helix angles were studied. The cutting force, machining tolerance and surface roughness were obtained. The AE signals appeared to have low values in up-milling rather than in down-milling. These are also appeared to have low values at low spindle revolutions rates. The cutting force values of Fxy and Fxyz were found to be increased according to the value of helix angle. In up-milling, it was difficult to find a definite tendency in machining tolerance, but in down-milling, machining tolerance of the different helix angle end mill was found to be lower than that of the convention end mill. There is a definite tendency that the surface roughness gets better as the RPM increases. In down-milling, Type $A(25^\circ+30^\circ)$ appeared to bring the most satisfactory result.

• Journal of Advanced Marine Engineering and Technology
• /
• v.36 no.7
• /
• pp.876-884
• /
• 2012

The worldwide CPV(Concentrated Photo Voltaic) market has been increased rapidly due to the increase in large-scale PV(Photo Voltaic) plants which are situated in sun-rich areas with either a Mediterranean or equatorial-type climate. CPV systems are arguably some of the most important devices in the production of electricity within regions with a sun-rich climate, particularly those which benefit from abundant direct solar irradiation. We have developed a 500X CPV module with rated power of 170Wp. The CPV module must satisfy the constraint of having a sensitive tracking accuracy due to the limited tolerance of the acceptance angle in intrinsic optical design. In this study, the module's acceptance angle used was designed with a tolerance angle of ${\pm}1^{\circ}$ in the secondary optics design. In general, non-concentrated module type 2-axis trackers have a tolerance angle larger than ${\pm}1^{\circ}$ due to standard silicon-type modules which are insensitive to the tracking accuracy of the sun. They have a tolerance angle of ${\pm}2{\sim}4^{\circ}$, which fails to exert a significant influence on the performance of the module. This paper provides a study of an experimental variation of the efficiency of the CPV module in terms of its tracking accuracy. Also, the performance of the module is studied from the perspective of temperature and direct irradiation.

• Journal of the Korean Society of Manufacturing Technology Engineers
• /
• v.19 no.5
• /
• pp.609-615
• /
• 2010

Angular contact ball bearings in a high speed spindles are under the extreme conditions, such as high temperature, big centrifugal force and thrust cutting forces. So, the assembly contacts between spindle shaft and inner ring bearings, bearing housing and outer ring of bearings are occasionally unstable at high speed revolution. Furthermore, the ball contact angle of a bearing, which influence stiffness and lifetime of bearings, are changed according to loads and rotational speed. To analyze internal forces of a bearing under high speed revolution, the ball contact are calculated using nonlinear equations in consideration of rotational speed, thrust loads and raceway form. Diameter increase of inner and outer ring by influence factors, such as internal forces to inner and outer ring, centrifugal force and temperature of inner and outer rings are calculated to establish stable state in bearing assembly in high speed spindle. Finally, contribution ratio of influence factor to assembly design tolerance of inner and outer rings are shown and the stable assembly design tolerance are proposed.

• Journal of the Optical Society of Korea
• /
• v.13 no.2
• /
• pp.227-233
• /
• 2009

We investigated the polarization-mode dispersion (PMD) tolerance for 40Gb/s non-return to zero (NRZ), duobinary NRZ, return to zero (RZ), carrier-suppressed RZ (CS-RZ), and duobinary-carrier-suppressed RZ (DCS-RZ) modulation formats with a forward error correction (FEC) coding. The power penalty has been calculated as a measure of the system performance due to PMD. After comparison of the PMD tolerance of various modulation formats, our results suggest that RZ signals have the best tolerance against the effect of first-order PMD only. The duobinary NRZ modulation format is most resilient to PMD when both first- and second-order PMD are considered. However, the duobinary NRZ modulation format is the most sensitive to the incident angle of the input signal to a fiber axis in the presence of first- and second-order PMD, leading to incident angle-dependent power penalty. The coding gain by FEC can cope with the power penalties induced by first- and second-order PMD up to a DGD value of 16ps.

• Steel and Composite Structures
• /
• v.7 no.3
• /
• pp.253-262
• /
• 2007

A methodology to design symmetrically laminated fibre-reinforced structures under transverse loads for minimum weight, with manufacturing uncertainty in the ply angle, is described. The ply angle and the ply thickness are the design variables, and the Tsai-Wu failure criteria is the design constraint implemented. It is assumed that the probability of any tolerance value occurring within the tolerance band, compared with any other, is equal, and thus the approach is a worst-case scenario approach. The finite element method, based on Mindlin plate and shell theory, is implemented, and thus effects like bending-twisting coupling are accounted for. The Golden Section method is used as the search algorithm, but the methodology is flexible enough to allow any appropriate finite element formulation, search algorithm and failure criterion to be substituted. In order to demonstrate the procedure, laminated plates with varying aspect ratios and boundary conditions are optimally designed and compared.

• Current Optics and Photonics
• /
• v.1 no.4
• /
• pp.351-357
• /
• 2017

This paper proposes a LED bicycle headlamp with a wide viewing angle to help bicyclists see the front effectively and because of its high visibility to reduce the risks of accidents around intersections or blind spots. The wide viewing angle was determined to be $28^{\circ}$ because it can illuminate a 5 m wide area 10 m away. Therefore, the road conditions of the intersection can be observed with the bicycle handlebar tilted slightly to the left or right. The headlamp has a compact reflector with a width of 30 mm, height of 27 mm, and length of 17 mm. Owing to its size, a change in the position of a light source leads to severe changes in light distribution. Therefore, the tolerance of the source position was analyzed by a simulation. The tolerance was ${\pm}0.5mm$ at the X, Y and Z axes within a less centered aiming range of ${\pm}1^{\circ}$. Finally, the prototype of the bicycle headlamp was made and the light distribution was measured by an automotive headlamp light measurement system. The experimental results indicate that the headlamp illuminates a 5 m wide area with an edge light of 3.2 lx as well as meeting the K-mark regulation.

• Journal of the Optical Society of Korea
• /
• v.18 no.6
• /
• pp.720-731
• /
• 2014

There are many kinds of optical systems to widen a field of view. Fisheye lenses with view angles of 180 degrees and omni-directional systems with the view angles of 360 degrees are recognized as proper systems to widen a field of view. In this study, we proposed a new optical system to overcome drawbacks of conventional omni-directional systems such as a limited field of view in the central area and difficulties in manufacturing. Thus we can eliminate the undesirable reflection components of the omni-directional system and solve the primary drawback of the conventional system. Finally, tolerance analysis using Zernike polynomial coefficients was performed to confirm the productivity of the new optical system. Furthermore, we established a method of optical axis alignment and compensation schemes for the proposed optical system as a result of tolerance analysis. In a sensitivity calculation, we investigated performance degradation due to manufacturing error using Code V(R) macro function. Consequently, we suggested compensation schemes using a lens group decentering. This paper gives a good guidance for the optical design and tolerance analysis including the compensation method in the extremely wide angle system.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 1995.10a
• /
• pp.977-980
• /
• 1995

This paper proposes the look ahead algorithm with the trapezoidal velocity trajectory in each G-code block. The algorithm requires the information on the length of next trajectories and the connecting angle between each trajectiories. A method of generating the maximum corner velocity upon the connecting angle within the machining tolerance is developed and applied to the look ahead algorithm. Simulations and experiments witha machining center show the effectiveness of the methodology.

• Journal of Dental Rehabilitation and Applied Science
• /
• v.24 no.1
• /
• pp.57-65
• /
• 2008

Purpose: Misfit of implant components was very important in terms of prosthodontics. they has been linked to prosthetic complications such as screw loosening and fracture. Although there are many results about rotational freedom or machining tolerance between fixture and abutments, the data about domestic implant systems are lacking. The aim of this in vitro study was to evaluate the rotational freedom of domestic external and internal connection implant systems between their fixtures/anlaogs and abutments comparing imported systems. Materials and Methods: Rotational freedom between abutments and fixtures/analogs was investigated by using digitalized rotational angle measuring device. (1) 1 domestic external connection system(Neobiotec) and 2 imported external connection systems(Nobel Biocare, Anthorgyr), (2) 1 domestic internal connection system(Dentium) and 4 imported external connection systems(Nobel Biocare, Anthorgyr, Straumann, Frident Dentsply), and (3) 1 domestic zirconia external connection abutment(ZirAce) were evaluated. Each group has 3 samples. Mean values for each group were analyzed. Results: The differences relative to rotational freedom between domestic and imported implant systems were observed but domestic external connection implant system showed about 2.67 degrees(in case of fixture) and internal connection system showed about 4.3 degrees(in case of fixture). Domestic zirconia abutment showed less than 3 degrees of rotational freedom in a situation where the abutment was connected to an implant fixture egardless of domestic or imported systems. Conclusion: Newly developed digitalized rotational angle measuring device has high measuring resolution. The rotational freedom of domestic implant systems were similar to imported implant systems.