The tungsten carbide is a material with high hardness, wear resistance, good chemical stability, and dimensional stability. Because of these characteristics, it is mainly used as a tool for cutting and molding such as molds, and casts required for manufacturing high value-added equipment such as automobile parts and medical equipment. However, it is difficult to process with the traditional machining methods because of the high toughness and hardness. To overcome these problems, a study of tungsten carbide machining processing using the ultrafast-laser was recently conducted. In this paper, the ultrafast lasers with the pulse duration of 190 fs, 5 and 10 ps, respectively, were used. When the experiments were conducted with pulse widths of 5 and 10 ps, respectively, micro-cracks were observed from the heat generated by the overlap of the laser pulses. Conversely, the machining processing using a laser with the pulse width of 190 fs showed a major advantage with no crack by minimizing the thermal effects.

In Korea, water spraying to suppress the dust during building dismantling operations has been done manually by human laborers, considered extremely dangerous since it often causes fatal accidents. Abroad, however, water spraying machines have been developed and used in construction sites instead of workers to prevent such serious industrial accidents. In this study, the first domestic water spraying machine is suggested. Since the spraying machine should have a novel dust tracking function, an optimal structure and mechanism should be designed to guarantee its motion performance. The motion for target tracking is achieved by the 2 DOF (Degrees of Freedom) structure comprising a linear and a rotary actuator. Then, the geometric analysis was performed to provide a sufficient kinematic workspace. Through the dynamic performance simulation, the optimal actuator capacities could be selected to generate an appropriate acceleration. The geometric and dynamic performance was evaluated by the extensive motion experiments. With this study, it is expected that an advanced water spraying machine can be developed only with domestic technologies to protect construction laborers from potentially dangerous accidents.

Since sCO₂ (Supercritical Carbon Dioxide) turbomachinery are generally small and operate at high rotational speed, the bearings remain a significant challenge to the design of the turbomachinery for the sCO₂ power cycles. However, a fluid induced instability similar to the oil whirl may occur even with the magnetic bearing under high pressure and high speed conditions of the sCO₂ turbomachinery. This paper presents experimental investigation on the instability of a sCO₂ compressor supported by the magnetic bearing. First, we introduce the sCO₂ compressor supported by the magnetic bearing. The procedure to guarantee the rotordynamic performance of the sCO₂ compressor supported by the magnetic bearing is provided. Then, the effects of the working condition such as the pressure and rotating speed on the fluid induced instability are investigated experimentally. Finally, a strategy to resolve the fluid-induced instability with conventional PID control is proposed and experimentally verified.

Electroadhesion has many advantages over other adhesion methods such as pneumatic, hydraulic, magnet, etc. The applications include electrostatic chucks and grippers. Recently, electroadhesion has been adopted for robots working in limited environments. The electro-adhesive climbing robots can be used for inspection and exploration in a variety of conditions. The electroadhesion robots often have a limited adhesion force. In this paper, we propose a novel pad structure improving the adhesion force. An additional insulating layer prevents the discharge from the high voltage application and increases the adhesion force per unit area. The electroadhesion forces were compared for the different pad materials and electrode structures and were partly confirmed as the theoretical model. The proposed pad was used for a climbing robot wheel. The climbing robot weighs approximately 3 kg and can manage to 3 kg of extra weight on metal walls. Experiments showed a 90-degree gradability for the climbing robot.

This paper addresses two methods to estimate the target incapacitation distance and probability of the arbitrary fragmentation warhead under the static detonation test condition. One is based on the probability equation suggested by Sperrazza and Kokinakis. The other is originated from the stationary detonation test concept to measure the performance of the fragmentation warhead. In the arbitrary fragmentation warhead, the target incapacitation probabilities obtained from the two methods were compared with each other. We found that the size of the fragment with cubic shape should be more than 3.5 mm to maximize the target incapacitation distance in the test method. And we also realized that the difference between the target incapacitation distance of the analysis method based on the test (AMBT) and that of the analysis method based on the probability equation (AMBPE) is decreased according to the increase of the fragment size. In conclusion, this paper can be useful for the estimation of the fragmentation warhead performance at the design stage.

The high voltage direct current (HVDC) device has been used to transmit electrical power with an advanced technology of semiconductors. The sustainable energy generation technologies of solar power and windmills are demanding that the HVDCs have high performance and reliability. In this regard, the cooling performance of the HVDC becomes a significant research topic because the temperature increase affects the operation of the device. The evaluation system to assess the cooling performance has been developed and is proposed in this paper. The experimental apparatus is presented in detail. Our experiments have shown the accuracy of flow rates, pressure drops, and the temperatures in the desired measurement points. We have successfully developed an evaluation system of the cooling performance of the HVDC device which has 2.48 kW of heat dissipation.

A measurement of a users’ motion is widely attracting attention for a realization of robotic assistance in daily activities. The soft, wearable sensing suit enables the monitoring of outdoor activities, with high wearability and insensitivity to inertial force. In this paper, we propose a novel sensing suit for measuring the multi degree of freedom (multi-DOF) motion of the wrist joints. We used a fabric-based capacitance-type stretch sensor for high adaptivity to a textile form of suits. The sensor was attached to the body link, instead of the wrist joint to reduce the interdependency among each joint axis and the effect of unwanted disturbance. We adopted the Deep Neural Network for calibration, and verified the higher estimation accuracy on the estimation of the multi-DOF wrist motions. The performance validation proceeded with comparing to the linear-based regression, and the root mean-squared error on the angle measurement was improved at slow motion and fast motion. A real-time measurement interface was developed and demonstrated with a frequency of 250 Hz.

In this paper, a multi-material non-assemble 3-DOF Force-Sensor was proposed and developed to improve the efficiency in the manufacturing. The PLA-Filament was used to produce the frame-structure and the elastic-deformation, and the conductive-PLA-filament, to produce a transducer. A dual-nozzle 3D-Printer was applied to produce the monolithic-structuretype force-sensor with the multi-materials simultaneously in single-manufacturing-process. The sensor was designed in a tripod-structure to detect the 3-DOF force-components in an external-force and a mechanical-interpretation was conducted on the elastic-deformation, which acts as a load-cell. The output model of a Wheatstone-bridge circuit-based transducer serving as a strain-gauge was also produced. A calibration-testing device, comprising a rotating stage, which turns with 2- DOF (θ, ϕ), was also developed to apply force in every direction. By conducting the calibration test, the relations between the input and output were computed in as a matrix and the resolution of the sensor was determined through the evaluation of linearity and stability deviations.

The necessity of converting toxic gas has arisen from the usage of perfluorinated compounds (PFCs), volatile organic compounds (VOCs), and hydrocarbon gases in the semiconductor process and laboratories. Also, recent strong regulations on the emission gas from vehicles also present the need for the highly efficient chemical conversion of toxic emission gases. In this study, we present the fabrication of platinum and ruthenium alloy metal catalysts on the yttria-stabilized zirconia balls, and the application of the metal catalysts to the catalytic converter for methane oxidation. The platinum and ruthenium alloy metal catalysts showed better performance than the platinum catalyst, i.e., 75% increase in the methane conversion efficiency at 500℃. Such improvement seems to be because of the facile oxygen supply from the ruthenium surface. Also, the platinum and ruthenium alloy catalysts with the doped cerium oxide interlayer showed better thermal stability than the platinum and ruthenium alloy metal catalysts, possibly because of the stronger bonding between the metal and oxide support.