• Journal of the Korean Society for Precision Engineering
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• v.18 no.5
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• pp.171-176
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• 2001

Plasma Display Panel(PDP) is a type of flat panel display utilizing the light emission produced by gas discharge. Barrier Ribs of PDP separating each sub-pixel prevents optical and electrical crosstalks from adjacent sub-pixels. Mold for forming barrier ribs has been newly researched to overcome the disadvantages of conventional manufacturing process such as screen printing, sand-blasting and photosensitive glass methods. Mold for PDP barrier ribs have stripes of micro grooves transferring glass-material wall. In this paper, Stripes of grooves of which width 48${\mu}{\textrm}{m}$ and 270${\mu}{\textrm}{m}$, depth 124${\mu}{\textrm}{m}$, pitch 274${\mu}{\textrm}{m}$ was acquired by machining hard and brittle materials of WC, Silicon, Alumina with dicing saw blade. Maximum roughness of the bottom and sidewall of the grooves was respectively 120nm, 287nm in grooving WC. Maximum tilt angle caused by difference between upper-most width and lower-most width was 2$^{\circ}$. Maximum Radius of bottom curvatures was 7.75${\mu}{\textrm}{m}$. This results satisfies the specification for barrier ribs of 50 inch XGA PDP if the groove form of mold was fully transferred to the barrier ribs. Barrier ribs were formed with Silicone rubber mold, which is transferred from grooved hard materials. Silicone rubber mold has elasticity accommodating the waveness of lower glass plate of PDP.

• Korean Journal of Optics and Photonics
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• v.24 no.5
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• pp.213-216
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• 2013

This paper presents a combination of linear Fresnel lenses optimized for ${\times}25$ solar concentration. The combined lens consists of $5{\times}5$ linear Fresnel lenses. Each Fresnel lens is of $10{\times}10$ mm and optimized to tilt the incoming light onto a solar cell of the same size. All of the optimized Fresnel segments have the same pattern height of 35 ${\mu}m$, draft angle of $4^{\circ}$, and edge groove round of 1 ${\mu}m$ but with different facet angles varying from $14.1^{\circ}$ to $31.2^{\circ}$. The solar concentrating efficiency of the combination is shown to be over 80% and more robust than a conventional single ${\times}25$ circular Fresnel lens in terms of pointing misalignment and manufacturing errors. A sensitivity analysis finds that the edge groove round should be kept as small as machining allows since the concentrating efficiency drops ~5% per 1 ${\mu}m$ increase of the edge groove.

• Journal of Veterinary Clinics
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• v.37 no.3
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• pp.135-140
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• 2020

The purpose of this study was to determine the outcome of distal femoral osteotomy for distal femoral varus and medial patellar luxation (MPL) grade 4 in small-breed dogs. Radiographs and medical records were reviewed to collect data and plan the surgery in small-breed dogs with MPL grade 4. Computed tomography (CT) imaging was also performed in cases of severe bone deformities. Signalment, weight, medial patellar luxation and lameness grade, radiographic bone union, complications, pre- and postoperative femoral varus angle, passive range of motion, static weight bearing distribution and visual analogue scale scores were recorded. Thirteen corrective distal femoral osteotomies were performed with ancillary and additional procedures in 9 dogs; 4 dogs had staged bilateral procedures; and four stifles were suspected to have partial or complete rupture of the cranial cruciate ligament. One stifle underwent patellar groove replacement. The mean ± SD pre- and postoperative femoral varus angles were 109.15°± 3.71° and 96.30°± 2.97°, respectively. Significant improvements in passive range of motion, thigh circumference and visual analogue scale (VAS) scores were observed. There was no reluxation of the patella. This study suggests that distal femoral osteotomy with traditional and additional procedures provided satisfactory outcomes in patient healing and functional recovery in small-breed dogs with excessive femoral varus angles.

• Journal of Veterinary Clinics
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• v.34 no.5
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• pp.366-369
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• 2017

A 30 kg, 6-year-old spayed female Samoyed dog was referred with a history of intermittent weight-bearing lameness in her right hindlimb for 3 weeks. The patient hadsurgery to correct a medial patellar luxation in the same limb 3 years prior. Based on the physical examination and radiographic findings, MPL and CCLR of the right hindlimb were diagnosed. Pre-surgical arthroscopy examination was performed, revealing a complete rupture of the cranial cruciate ligament, medial caudal meniscal tears and fibrotic cartilagechanges on the trochlear groove. An arthroscopy-assisted partial meniscectomy was used to repair themedial caudal meniscus. To correct the tibial plateau angle and medial patellar luxation, a tibial plateau leveling osteotomy (TPLO) was performed. A tibial tuberosity transposition (TTT) was performed to realignthe quadriceps mechanism with the trochlear block recession followed by soft tissue reconstruction. The post-surgical recovery was uneventful, and the patient was weight-bearing with normal ambulation on the repaired limb. There were no complications, and the implants were well positioned at the last follow-up. The clinical outcome of the caseindicates that combining TPLO with TTTis a good surgical option for treatingconcurrent CCLR and MPL.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.05a
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• pp.748-752
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• 2004

Fluid dynamic bearings (FDBs) have been replacing ball bearings of the HDD spindle motor very rapidly. But there are several demerits of HDB, such as high friction torque, variable viscosity of the fluid lubricant depending on operating temperature, low stiffness, and etc. Eccentricity is one of the major parameters which affects the static and dynamic characteristics. As the static eccentricity is larger, the stiffness and the damping coefficients become bigger. But friction torque is relatively unaffected by the static eccentricity. This research proposes a new type of journal bearing with asymmetric journal grooves which results in better dynamic characteristics. The static and dynamic characteristics of the new journal bearing are investigated by solving the Reynolds' equation with FEM, and the transient analysis is performed to predict the dynamic behavior of rotor by solving the equations of motion of a HDD spindle system with Runge-Kutta method. The result shows that the proposed Journal bearings have much bigger stiffness and damping coefficients compared with the conventional symmetric ones. And consequently, it has smaller whirl radius and tilting angle.

• Structural Engineering and Mechanics
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• v.67 no.1
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• pp.45-52
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• 2018

Several techniques have been developed for shear strengthening of reinforced concrete (RC) members by using fiber reinforced polymer (FRP) composites. However, debonding of FRP retrofits from concrete substrate still deemed as a challenging concern in their application which needs to be scrutinized in details. As a result, this paper reports on the results of an experimental investigation on shear strengthening of RC beams using near surface mounted (NSM) FRP reinforcing bars. The main objective of the experimentation was increasing the efficiency of shear retrofits by precluding/postponing the premature debonding failure. The experimental program was comprised of six shear deficient RC beams. The test parameters include the FRP rebar spacing, inclination angle, and groove shape. Also, an innovative modification was introduced to the conventional NSM technique and its efficiency was evaluated by experimental observation and measurement. The results testified the efficiency of glass FRP (GFRP) rebars in increasing the shear strength of the test specimens retrofitted using conventional NSM technique. However, debonding of FRP bars impeded exploiting all retrofitting advantages and induced a premature shear failure. On the contrary, application of the proposed modified NSM (MNSM) technique was not only capable of preventing the premature debonding of FRP bars, but also could replace the failure mode of specimen from the brittle shear to a ductile flexural failure which is more desirable.

• Tribology and Lubricants
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• v.8 no.2
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• pp.64-72
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• 1992

The recent trends of rotating machinery demand high speed and high temperature operation, and the bearing with new material is required to be developed. Ceramic, especially silicon nitride, have been receiving attention as alternative material to conventional bearing steel. Ceramic ball bearing offers major performance advantages over steel bearing, for instance, high speed, maginal lubrication, high temperature, improved corrosion resistance and nonmagnetic capabilities etc.. In this paper, the mechanical characteristics of ceramic ball bearing (hybrid ceramic bearing and all ceramic bearing) were investigated, and the characteristics of ceramic bearing were compared with that of steel bearing. Deep groove ball bearing 6208 was taken the object of analysis. The main results of analysis were followings: the radial stiffness of hybrid and all ceramic bearing were 112% and 130% that of steel bearing, and the axial stiffness of all ceramic bearing was 110% that of steel bearing. According as rotating speed was up, the ball load, the contact angle, the contact stress and the spin-to-roll ratio between ball and raceway of ceramic bearing were far smaller than these of steel bearing. And there was not a significant difference between the minimum film thickness of ceramic bearing and steel bearing. It is expected that this research is contributed to enhanced fundamental technology for the practical applications of ceramic ball bearing.

• Journal of the Korean Society for Precision Engineering
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• v.18 no.5
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• pp.130-136
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• 2001

Generally, a metal slitting saw is plain milling cutter with thickness less than 3/16 inch. This is used for cutting a workpiece that high dimensional accuracy and surface finish is necessary. A small thin milling cutter like a metal slitting saw is useful for machining a narrow groove. In this case, built up edge(BUE) is severe at each tooth and affects the surface integrity of the machined surface and tool wear. It is well known that tool geometry and cutting conditions are decisive factors to remove BUE. In this paper, we optimized the geometry of the milling cutter and selected cutting conditions to remove BUE by the experimental investigation. The experiment was planned with Taguchi method based on the orthogonal array of design factors such as coating, rake angle, number of tooth, cutting speed, feed rate. Response table was obtained from the number of built-up edge generated at tooth. The optimized tool geometry and cutting conditions could be determined through response table. In addition, the relative effect of factors was identified bh the analysis of variance (ANOVA). Finally, coating and cutting speed turned out important factors for BUE.

• Journal of Welding and Joining
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• v.33 no.1
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• pp.41-48
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• 2015

In this study, the effect of heat input on weld metal microstructure and the effects of dissimilar weld heat affected zone in quenched and tempered ASTM A517 on the stainless steel AISI 316L is investigated through the optimization of welding parameters. For this purpose, two welding techniques are used, tungsten-conventional gas and pulsed gas with weld wire ER 309MoL with Diameter 2.4 mm. Research showed that the grain size of the heat affected zone in pulsed welding is less compared with conventional welding; weld metal structure is fully austenitic, it has a finer structure in the pulsed method. Additionally, the growth of weld metal adjacent steel A517 is different from steel 316L. Further, investigation showed that the rate of dilution is less in the pulsed method and the impact energy is increased in each three regions of the weld metal and heat affected zones in the pulsed method; the fracture in the weld metal and heat affected zone of steel 316L is quite soft and it is semi-crispy in the heat affected zone of steel A517.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.09a
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• pp.175-180
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• 2005

In this study, we have developed a novel wire straightener which uses the direct heating method (DHM) fer straightening the micro wire. Also, we have developed a shearing device for cutting the micro wire. In order to avoid the surface oxidization, we supplied the inert gas(Ar) during the heating process and examined the effect of gas flow rate. The effects of the tension and the current applied to the tungsten micro wires were also thoroughly studied. From various experiments and analyses, we could obtain fine straightness $(\approx1\;{\mu}m/1000\;{\mu}m)$ and roundness $(<{\pm}2{\mu}m\;/100{\mu}m)$ when the tension is $500\~~600gf$ and the current is about 1.5A. for burrfree cutting, counter-punch method which two cutters moving contrary was used. The cutting blade has various U-groove angle where upper $10^{\circ}$, $mid:25^{\circ}$, lower $0^{\circ}$. After the shearing process, we confirmed the shearing section.