The plate for the multi-stage reducer is a component of a traveling motor and is required for high wear resistance and maintaining precision. The plates that are mainly manufactured by the press process have burrs on the edges of the material after the general press shear process. Since burrs have a great influence on assembly and shape precision according to product characteristics, a post-treatment process for removing burrs is mandatory, and several studies have been conducted on this topic. In this study, a flattening process was developed to remove the burrs. First, the piercing and blanking process forming analysis was performed to find the process conditions for burr removal. Subsequently, the flattening process forming analysis was performed, and the reliability of the analysis was verified through an experiment using the derived process conditions.
E-Beam micro-hole drilling features high productivity of 2,000 holes per second and a high aspect ratio of 10 (depth/diameter). It can be used for the fabrication of nozzles and filters that require several holes. The hole-formation mechanism comprises 1) melting the sample by the energy exchange of e-beam and 2) removing the molten sample by the explosion of the backing material. Accordingly, hole-formation mechanism studies have focused on the effectiveness of backing material and the workpiece’s melting characteristic. This study investigated the melting depth characteristics depending on the beam current and exposure time that determines the E-Beam dose. The experiments were conducted without using the backing materials with an aim to investigate the melting characteristic of the workpiece itself. The results showed that the increase in the exposure current led to an improvement in the melting depth. The results were verified based on the comparison with the results of the process involving the backing material.
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Micro CT Analysis of Microholes Drilled by Focused Electron Beam Drilling Based on Image Noise Reduction Using Masking Layers Hyunmin Park, Joon-Goo Kang, Jin-Seok Kim, Eun Goo Kang, Hyung Wook Park, Jaewoo Seo Journal of the Korean Society of Manufacturing Technology Engineers.2022; 31(6): 388. CrossRef
The controller for the power assist robot that is in constant contact with the user requires to be sensitively controlled as per the user"s intention and maintain control stability to ensure the user"s safety. Admittance control is generally used for human intention-based force control. By setting the parameters of the admittance control at a low level it is possible to sensitively control according to the user"s intention. However, too sensitive settings make the system unstable. Therefore, it is difficult to set a fixed admittance parameter in a power assist robot in which dynamics change with an increase in load mass. Consequently, we propose a variable admittance control strategy according to the load mass. The proposed method responds sensitively to the user"s intention by setting the admittance parameters at low during no-load action and ensures stability by setting the admittance parameter high when transmitting high loads. In simulation with a carrying load of 30 kg, the proposed method requires half the interaction force compared with a fixed admittance control when decelerating and has twice faster settling time when stopped. In addition, through experimental verifications, the variable admittance control was proven to reduce the user"s load by 70% compared to load mass.
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A Study of Admittance Force Control for FSW of Hybrid Machine In-Gyu Park, Byeongjae Kim, Jungwoo Lee, Jongdeuk Lee, Seongjun Moon Journal of the Korean Society of Manufacturing Technology Engineers.2023; 32(2): 109. CrossRef
Plastic deformation of balls in safety coupling by collision with V-Hole was investigated in the current study. Generally, when the applied torque is greater than the maximum allowable torque, balls in V-Hole get out from the holes and the coupling loses the torque transfer capability. After balls are out from the V-Holes, the balls and V-Hole rotate at a different velocity. When balls meet the next V-Hole, they collide into the wall of the V-Hole. Due to this collision, plastic deformation and wear take place. The plastic deformation and wear may reduce the torque transfer capability of the safety coupling. The reduction in torque transfer capability was observed in the experiment. In this study, plastic deformation of balls and flange was investigated through dynamic analysis of the safety coupling. Also, the effect of relative rotational velocity on the plastic deformation was investigated.
With the progress of flexible devices, numerous researchers aim to manufacture the flexible battery with freefrom at various scales. Laser cutting is considered as one of the essential processes to achieve on-demand manufacturing but continuous wave or long-pulse laser beam may cause large heat affect zone (HAZ) in cutting edge and may even result in failure of battery function. Herein, it was demonstrated that the sophisticated cutting process using ultra-short pulse laser is applicable for tailoring of flexible battery with multilayered structure. Based on the comparison of cutting results using nanosecond laser and femtosecond laser, we confirmed that laser cutting by femtosecond laser induces much less thermal damage on thin foil electrodes, separator, and electrolyte. Furthermore, we investigated the interaction of femtosecond laser with the materials composed of a flexible battery and implemented a process for cutting each material without causing any critical damage. To prevent a short circuit between the anode and cathode, which usually occurs during laser cutting of the actual battery, the double-side cutting process was done by adjusting the focal points of the laser beam. We assume that the proposed approach can be applied in a roll-to-roll based cutting process for the mass-production of flexible devices.
Anodic aluminum oxide (AAO) is widely used in various industrial fields to increase the mechanical property or corrosion resistance of the product surface. In this study, mechanical properties were measured according to the thickness of AAO through the nanoindentation test. The maximum indentation load, elastic modulus, and hardness were measured for different thicknesses of AAO. It was confirmed that the majority of the mechanical property values increased with the thickness. Various fracture shapes based on the thickness were analyzed by observing pressure marks on the surface using FE-SEM equipment. Apparently, it is proposed that the optimum AAO thickness with desired mechanical properties can be obtained, which is expected to possess immense economic value as per the optimization of the production time of AAO based products.
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In-situ Wired and Wireless Material Testing System with Nanometer-level Displacement Control Kyoung Seok Park, Pill Ho Kim, Chung-Seog Oh Journal of the Korean Society for Precision Engineering.2024; 41(11): 881. CrossRef
The purpose of this study was to compare ankle joint loads (Linear and Angular Impulses) while descending the stairs and ramp. Ten young male subjects participated in this study. Stairs and ramp of identical slope (30 degrees) were custom-made to include force plates in the middle of pathways. Subjects descended the stairs and ramp at a comfortable speed and posture. The stance period was divided into three phases, weight acceptance (WA), single limb stance, and pre-swing. Three-directional impulses and their sum were derived from the reaction forces and moments at the ankle joint. Differences in impulse sums (Both Linear and Angular) between stairs and ramp were significant only in the early (WA) phase, whereas those of stairs were greater than the ramp. All subjects adopted forefoot strike strategy for the stairs and 80% of the subjects adopted rearfoot strike strategy for the ramp. An increase in the GRF and moment arm of the GRF at the ankle joint in case of forefoot strike may have contributed to the increase in the linear and angular impulse in the early phase of stair descent compared to ramp descent. The results are in agreement with the preference of ramp in the elderly.
Estimation of the relative position between the body segments is an important task in inertial sensor-based human motion tracking. Conventionally, the relative position is determined using orientations and constant segment vectors that connect from segment to joint center, based on the assumption that the segments are rigid. However, the human body segments are non-rigid, which leads to an inaccurate relative position estimation. This paper proposes a relative position estimation method based on inertial sensor signals, considering the non-rigidity of the human bodies. Considering that the effects of non-rigidity are highly correlated with a specific variable, the proposed method uses time-varying segment vectors determined by the specific physical variable, instead of using constant segment vectors. Verification test results for an upper-body model demonstrates the superiority of the proposed method over the conventional method: The averaged root mean square error of the sternum-to-forearm estimation from the conventional method was 34.19 ㎜, while the value from the proposed method was 16.67 ㎜.
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Wearable Inertial Sensors-based Joint Kinetics Estimation of Lower Extremity Using a Recurrent Neural Network Ji Seok Choi, Chang June Lee, Jung Keun Lee Journal of the Korean Society for Precision Engineering.2023; 40(8): 655. CrossRef
Ergonomic guidelines for the design interfaces of additive modules for manual wheelchairs: sagittal plane Bartosz Wieczorek, Mateusz Kukla, Łukasz Warguła, Marcin Giedrowicz Scientific Reports.2023;[Epub] CrossRef
Effects of the Selection of Deformation-related Variables on Accuracy in Relative Position Estimation via Time-varying Segment-to-Joint Vectors Chang June Lee, Jung Keun Lee JOURNAL OF SENSOR SCIENCE AND TECHNOLOGY.2022; 31(3): 156. CrossRef
Application of Artificial Neural Network for Compensation of Soft Tissue Artifacts in Inertial Sensor-Based Relative Position Estimation Ji Seok Choi, Jung Keun Lee Journal of the Korean Society for Precision Engineering.2022; 39(3): 233. CrossRef
In this study, both mechanical power and the wind speed distribution in the wake of a wind turbine scaled model were analyzed using a commercial CFD program (Ansys CFX) along with experimental validation. For the simulation, two different turbulence models including the SST model and the k-ε model were used. The scaled model was originally designed and manufactured by the researchers at the Technical University of Munich and was slightly modified for this research. To experimentally verify the CFD results, tests were performed with the scaled model under the turbulent wind in a wind tunnel. From the experimental validation, it was found that the k-ε turbulence model gives a better prediction than the SST model in the wake results. However, the SST turbulence model showed better prediction than the k-ε turbulence model in the power prediction. The discrepancy between the CFD results and the experimental validation is partially due to the fact that the blades are deformed at all times and control of pitch in the rated power region but these aspects are not considered in the simulation. If a transient analysis is performed using LES models, it will more accurately predict the change of wake with high turbulence intensity.
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Design and Performance Analysis for 3 MW Waste Pressure Steam Turbine Using 2D and 3D Numerical Simulation Hwabhin Kwon, Jong Yun Jung, Joon Seob Kim, Ye Lim Jung, Heesung Park Journal of the Korean Society for Precision Engineering.2021; 38(6): 455. CrossRef
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