• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.6
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• pp.170-177
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• 2020

This study examined the clamping force control method and the braking performance test results of an electromechanical brake (EMB) using braking test equipment. Most of the studies related to EMBs have been carried out in the automotive field, dealing mainly with the static test results for various control methods. On the other hand, this study performed a dynamic performance evaluation. The three-phase interior permanent magnet synchronous motor (IPMSM) was applied to drive the actuator of the EMB, and the analysis was verified by JMAG(Ver. 18.0), which is finite element method (FEM) software. The current control, speed control, and position control were used for clamping force control of the EMB, and the maximum torque per ampere (MTPA) control was applied to the current controller for efficient control. The EMB's emergency braking deceleration performance was tested in the same way as conventional pneumatic brake systems when the wheel of a train rotates at 110 km/h, 230 km/h, and 300 km/h. The emergency braking time, with the wheel stopped completely at the maximum rotational speed, was approximately 73 seconds. The similarity of the braking time and deceleration pattern was verified through a comparison with the performance test results of the pneumatic brake system applied to the next generation high-speed railway vehicle (HEMU-430X).

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.1
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• pp.107-114
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• 2017

A turbocharger is an engine supercharger that is driven by exhaust gas. It improves the output and fuel efficiency by increasing the charging efficiency of the mixture gas, which is achieved by changing the rotatory power of the turbine connected to the exhaust passage. It is important to control the supercharging for this purpose. A nozzle slide joint is one of the core parts. Austenitic stainless steel is currently used as the material for this part, and its excellent mechanical properties include high heat resistance and corrosion resistance. However, because of its poor machinability, there are many difficulties in producing products with complicated shapes. Machining is used in the production of nozzle slide joints for high dimensional accuracy after metal powder injection molding. As design variables in this study, we investigated the sintering temperature, product stress, deformation rate, radius of curvature of the punch, and angle of the chamfer punch, which are related to the strain and shapes. The goal is to suggest a forming process using Nitronic 60 that does not require machining to manufacture a nozzle slide joint for a turbocharger. Accordingly, we determined the best process environment using finite-element analysis, the signal-noise ratio, and the Taguchi method for experiment design. The relative density and hydrostatic pressure of the final product were in accordance with the results of the finite element analysis. Therefore, we conclude that the Taguchi method can be applied to the design process of metal powder injection molding.

• The korean journal of orthodontics
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• v.39 no.2
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• pp.95-104
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• 2009

Objective: The purpose of this study was to evaluate the effect of length and shape of cutting flute on mechanical properties of orthodontic mini-implants. Methods: Three types of mini-implants with different flute patterns (Type A with 2.6 mm long flute, Type B with 3.9 mm long and straight flute, Type C with 3.9 mm long and helical flute) were inserted into the biomechanical test blocks (Sawbones Inc., USA) with 2 mm and 4 mm cortical bone thicknesses to test insertion and removal torque. Results: In 4 mm cortical bone thickness, Type C mini-implants showed highest maximum insertion torque, then Type A and Type B in order. Type C also showed shortest total insertion time and highest maximum removal torque, but Type A and B didn't showed statistically significant difference in insertion time and removal torque. In 2 mm cortical bone thickness, there were no significant difference in total insertion time and maximum removal torque in three types of mini-implants, but maximum insertion torque of Type A was higher than two other Types of mini-implants. Conclusions: Consideration about length and shape of cutting flute of mini-implant is also required when the placement site has thick cortical bone.

• Journal of the korean academy of Pediatric Dentistry
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• v.28 no.2
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• pp.261-270
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• 2001

This study was performed to evaluate wear characteristics of light-cured composites when opposed by human enamel. Seven light-cured restorative composites were selected and enamel cusps sectioned from premolars. All samples were stored in distilled water at $37^{\circ}C$ for 10 days. 68.6 N of weight was loaded during the test. The measurements of vertical loss of enamel cusps, weight loss and volume loss of composites, and SEM observations of the polished and abraded surfaces were made after 30,000 cycles. The results obtained were summarized as follows; 1. The highest hardness value of 70.4 was observed in the Spectrum group and the lowest value of 19.8 was observed in the Heliomolar group. Results of Tukey test showed that an overall significant difference was indicated except the Spectrum, Z100 and Clearfil AP-X groups(p<0.05). 2. Enamel showed the good abrasion resistance against the Heliomolar group of microfilled composite and the Palpique Toughwell group containing the submicron hybrid type spherical fillers. 3. The abrasive wear resistance of hybrid composites was improved with the decrease of mean particle size and hybrid of submicron particle fillers. 4. SEM observation of worn surfaces revealed the protrusion, attrition and missing of fillers, cracks developing and delamination in the matrix.

• The Proceedings of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.9 no.2
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• pp.58-67
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• 1995

The paper describes the variation of magnetic fields caused by the operation of induction motors. The measuring system consists of the self-integrating magnetic field sensor, amplifier, and active integrator. From the calibration experiments, the frequency bandwidth of the magnetic field measuring system ranges from 20[Hz] to 300[kHz] and sensitivity is 0.234(mV/$\mu\textrm{T}$]. The magnetic fields generated under steady state and starting operations of duction motor are recorded by the proposed measuring system, and the fast Fourier transformation(FFT) of the measured data is performed to analyze the harmonic components. A single pulsed magnetic field is strongly caused by direct starting the induction motor, and its peak value is greater than 5 times as compared with the steady state value. The long transient duration and high intensity originates from the large inductance and dynamic characteristic of the induction motor, During the steady state operation of induction motor, subharmonics of magnetic field components, which depend on the pole number of induction motor, are observed. The lower order power-line harmonics can be inferred from the voltage flicker and current ripple which are derived from the torque fluctuation of induction motor. In the case of the induction motor drived by inverter, the harmonics of magnetic field are much more than those caused by direct starting method and are found generally to increase with decreasing the driving frequency.

• Journal of the Korean Society for Marine Environment & Energy
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• v.10 no.4
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• pp.187-192
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• 2007

Impact on cylindrical surface caused by plunging breaking waves is investigated experimentally. The breaking waves are generated in a wave flume by decreasing the wave maker frequencies linearly and focusing the generated wave components at one specific location. The breaking wave packets are based on constant wave steepness spectrum. Three inclination angles of cylinder are applied to examine the effect of contact angle between cylinder and front surface of breaking waves. Also, the effect of cylinder diameter on pressure distribution and its peak value is investigated by adopting three cylinders with different diameters. The longitudinal location of cylinder is slightly moved in eight different points to find out a probable maximum value of impact pressure. The pressures and total force on cylinder surface are measured by piezo-electric pressure sensors and 3-components load cell with 30kHz sampling rate. The variation of peak impact pressures and forces is analyzed in terms of cylinder diameter, inclination angle and location. Also, the pressure distribution on cylindrical surface is examined. The cylinder location and surface position are more important parameters that govern the magnitude and shape of peak pressures, while the cylinder diameter and inclined angle are relatively insignificant. In a certain conditions, the impact phenomenon becomes very unstable which results in a large variation of measured valves in repeated runs.

• Journal of the Institute of Convergence Signal Processing
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• v.11 no.4
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• pp.338-344
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• 2010

Both ends of welding line are often closed by wall in the welding of ship blocks. In this research, seam tracking sensing system for butt welding in the condition with wall was developed. Seam tracking sensing system measures position of carriage from wall and detects root-pass of welding line. The system consists of the laser displacement sensors and ultrasonic sensors. The laser displacement sensor reciprocal1y rotates by the motor and measures a distance from laser sensor to the welding material. The ultrasonic sensor measures a distance between welding system and walls. The distance measured by the ultrasonic sensor is used to get X(driving) position and to determine initial and end point of the weld line. Y(weaving) and Z(height) of the weld line are obtained by the distance measured by the laser displacement sensor and the orientation of the sensor. The sensing system includes the controller that is independent from the welding carriage. The seam tracking sensing system is attached to both side of welding carriage so that interference between welding torch and sensing system can be avoided during the welding. And both side sensing system minimize dead zone. Finally, developed sensing system was adhered to welding carriage and verified usefulness by experiments.

• Korean Journal of Agricultural Science
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• v.12 no.1
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• pp.101-107
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• 1985

Since most farmers breeding livestocks in Korea is depended on imported feeds, the rate of self-supplying feeds is very important for a stable development of farmers. Therefore, it is considered necessary to increase the rate of self-supplying feeds. In this study, performance tests were carried out with barley and forage to find the design's parameters of hammer for a small size hammer mill which can be driven by 3.7-7.5 kW power tiller being used by most farmers. The revolution speed of hammer mill was 3000 rpm, widths of hammer were 20mm, 30mm, 40mm, and the levels of thickness of hammer were 2mm, 4mm and 6mm. Experimental materials used were barley and forage and screen openings for barley was 4.76mm, and 3.18mm for forage. The study results can be summarized as follows; 1. Results of grinding tests showed that particle sizes were 478-774 microns for barley and 350-434 microns for forage. They were decreased according to the increasing thickness and width of hammer. 2. Fineness modulus of grinded materials were 3.07-3.62 for barley and 2.69-2.93 for forage. They were inversely proportional to thickness and width of hammer. 3. The required power for grinding was 3.8-5.0 kW for barley and 0.9-1.4 kW for forage. The thickness of hammer was more important for less power requirement than width of hammer. 4. Grinding performance of a small size hammer mill was 99-170kg/kWh for barley and 11-21 kg/kWh for forage. The thickness of hammer was an important factor for grinding performance, and inversely proportional to grinding performance. For about 3.2 of fineness modulus, 4 mm thickness was the best, and an optimum width of hammer was 30mm for a small size hammer mill.