• Tribology and Lubricants
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• v.35 no.3
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• pp.158-168
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• 2019

This paper presents the investigation of two types of rotordynamic modeling issues for 2.2 kW-class, rated speed of 1,800 rpm, squirrel-cage type induction motors. These issues include the lamination structure of rotor cores, and the radial clearance of ball bearings that support the shaft of the motor. Firstly, we focus on identifying the effects of rotor core lamination on the rotordynamic analysis via a 2D prediction model. The influence of lamination is considered as the change in the elastic modulus of the rotor core, which is determined by a modification factor ranging from 0 to 1.0. The analysis results show that the unbalanced response of the rotor-bearing system significantly varies depending on the value of the modification factor. Through modal testing of the system, the modification factor of 0.079 is proven to be appropriate to consider the effects of lamination. Next, we investigate the influence of ball bearing clearance on the rotordynamic analysis by establishing a bearing analysis model based on Hertz's contact theory. The analysis results indicate that negative clearance greatly changes the bearing static behavior. Rotordynamic analysis using predicted bearing stiffness with various clearances from -0.005 mm to 0.010 mm reveals that variations in clearance result in a slight difference in the displacement of the system up to 18.18. Thus, considering lamination in rotordynamic analysis is necessary as it can cause serious analysis errors in unbalanced response. However, considering the effect of the bearing clearance is optional because of its relatively weak impact.

• Journal of the Society of Naval Architects of Korea
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• v.57 no.5
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• pp.287-296
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• 2020

The present study aims to improve the accuracy of the maneuvering simulations based on captive model test results. To derive the hydrodynamic coefficients in a self-propelled condition, a mathematical maneuvering model using a whole vehicle model was established. Captive model tests were carried out using the Vertical Planar Motion Mechanism (VPMM) equipment. A motor controller was used to control the constant propeller revolution rate during pure motion tests. The resistance tests, self-propulsion tests, static drift tests, and VPMM tests were performed in the towing tank of Seoul National University. When the vertical drift angle changes, the gravity load on the sensors were changed. The hydrodynamic forces were deduced by subtracting the gravity load from the measured forces. The hydrodynamic coefficients were calculated using the least-square method. The simulation of the turning circle test was compared with the free-running model test result, and the error of the turning radius was 8.3 % compared to the free-running model test.

• Korean Journal of Metals and Materials
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• v.46 no.10
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• pp.672-682
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• 2008

The resistance spot welding of TRIP590 steels was investigated to enhance understanding of weld fracture during tensile-shear strength (TSS) test. The main failure modes for spot welds of TRIP590 steels were nugget pullout and interfacial fracture. The peak load to cause a weld interfacial failure was found to be related to fracture toughness of the weld and the weld diameter. Although interfacial fracture occurred in the samples, the load carrying capacity of the weld was high and not significantly affected by the fracture mode. Substantial part of the weld exhibits the characteristic dimple (or elongated dimple) fractures on interfacial fractured surface, in spite of the high hardness values associated with the martensite microstructures. The high load-bearing ability of the weld is directly associated with the area of ductile fracture occurred in weld. Therefore, the judgment of the quality of resistance spot welds in TRIP590 steels, the load carrying capacity of the weld should be considered as an important factor than fracture mode.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.23 no.12
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• pp.1506-1513
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• 2019

Recently, as the industrial scope of multi-rotor unmanned aerial vehicles(UAV) is greatly expanded, the demands for data collection, processing, and analysis using UAV are also increasing. However, the acoustic data collected by using the UAV is greatly corrupted by the UAV's motor noise and wind noise, which makes it difficult to process and analyze the acoustic data. Therefore, we have studied a method to enhance the target sound from the acoustic signal received through microphones connected to UAV. In this paper, we have extended the densely connected dilated convolutional network, one of the existing single channel acoustic enhancement technique, to consider the inter-channel characteristics of the acoustic signal. As a result, the extended model performed better than the existed model in all evaluation measures such as SDR, PESQ, and STOI.

• Physical Therapy Rehabilitation Science
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• v.11 no.2
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• pp.235-244
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• 2022

Objective: The aim of this study was to investigate of the foot plantar pressure and usability after gait training using the ExoAtlet wearable exoskeleton robot in an incomplete spinal cord injury (SCI) patient. Design: A case study Methods: Six participants with an asymmetry in motor and sensory function completed the gait training using ExoAtlet wearable exoskeleton robot for 15 sessions, five per weeks, 3weeks. They were divided into two groups (low and high strength group) and group differences were evaluated about session at stating of gait, gait distance at final session and foot plantar pressures and useability after training. Results: Low strength group was faster than high strength group on adaptation of robot gait. And high strength group increased faster than low strength group on the gait distance during training. In standing and gait, weaker leg was higher than stronger leg on mean foot plantar pressure in low strength group. And stronger leg was higher than weaker leg on foot plantar pressure in high strength group. The length of the anterior-posterior trajectory of the center of pressure during gait was similar in low strength group, but different in high strength group. useability was positive about ExoAtlet wearable exoskeleton gait after training. Conclusions: ExoAtlet wearable exoskeleton robot gait training was positive about improving gait in all participants regardless of differences in severity of symptoms and gait abnormalities.

• Journal of Drive and Control
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• v.19 no.4
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• pp.36-45
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• 2022

The aim of this study was to verify an E-driving system of a 44 kW-class electric tractor using agricultural workload data. Workload data were acquired during field test (plow tillage, rotary tillage, loader operation, field driving, asphalt driving) using a conventional tractor with a load measurement system. These workload data were converted to data of a 44 kW-class tractor based on the load factor of the engine. These data were used to verify the design of the E-driving system of an electric tractor. High-load operations such as plow tillage, rotary tillage, and loader operation could be performed at stage L and stage M. High-speed operation (asphalt driving) could be effectively performed at stage H using a rated rotational speed of the motor. As a result, the E-driving system of the electric tractor was possible to perform all major agricultural operations according to gear stages of range shift. Based on results of this research, we plan to develop an electric tractor equipped with an E-driving system and conduct research on actual vehicle verification in the future.

• KIPS Transactions on Software and Data Engineering
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• v.11 no.5
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• pp.221-228
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• 2022

With the application of artificial intelligence technology, robots can provide efficient services in real life. Unlike industrial manipulators that do simple repetitive work, this study presented design methods of 6 degree of freedom robot arm and intelligent object search and movement methods for use alone or in collaboration with no place restrictions in the service robot field and verified performance. Using a depth camera and deep learning in the ROS environment of the embedded board included in the robot arm, the robot arm detects objects and moves to the object area through inverse kinematics analysis. In addition, when contacting an object, it was possible to accurately hold and move the object through the analysis of the force sensor value. To verify the performance of the manufactured robot arm, experiments were conducted on accurate positioning of objects through deep learning and image processing, motor control, and object separation, and finally robot arm was tested to separate various cups commonly used in cafes to check whether they actually operate.

• Journal of the Korean Society of Industry Convergence
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• v.25 no.6_2
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• pp.1097-1102
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• 2022

With the continuous development of the current industry, the current global environment is in a very serious situation, with resource supply and demand dependent on imports and huge costs for waste disposal due to the depletion of resources and mass generation of industrial waste. Its limitations have already been revealed in many fields, and the importance of re-manufacturing is drawing attention as a countermeasure to these problems. Re-manufacturing aims to recover products that are in the aging and disposal stages, recover to performance close to new products, and re-commercialize them. Among them, most of the machine tools are made of materials such as steel and cast iron with large structures, and raw materials are widely used when producing new products. In addition, since a lot of carbon is generated due to production, it is an object that can obtain a great re-manufacturing effect. Planner millers belonging to large machine tools are one of the machine tool equipment that can greatly reduce resources and energy through re-manufacturing because the structure is very large and the casting is several to tens of tons. Through this machine tool, performance tests and results are derived on the development of re-manufacturing source technology and domestic servo motor and CNC control device.

• Textile Coloration and Finishing
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• v.35 no.2
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• pp.128-136
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• 2023

Recently, the automobile industry is developing as the demand for automo- biles increases due to industrial development and population growth. In addition, many studies are being conducted to reduce heat loss inside the automobiles in order to save energy inside the automobiles due to environmental regulations. In this study, alumina, nanosilicon, and aerogel, which are adiabatic materials, were filled in PET to manufacture yarn, identify physical and mechanical properties, and weave into fabric to confirm adiabatic performance. As the content of the adiabatic material increased, the tensile strength of the fibers filled with alumina and nanosilicon decreased greatly, and the adiabatic property slightly increased. The tensile strength of fibers filled with the aerogel decreased slightly, but the adiabatic properties were greatly increased. Therefore, it is considered to be due to the large volume fraction in the PET yarn due to the low density of the aerogel.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.34 no.3
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• pp.222-237
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• 2024

Objectives: This study aims to assess the current status of work environment measurement (WEM) for carcinogenic, mutagenic, reproductive toxic substances and to identify their high-risk industries for hazard surveillance and risk assessment. Methods: WEM Data from 37 specially managed CMR substances (2018-2022), the high-risk industries were identified by using estimated 95th percentile levels (X_0.95) of measurements compared with the occupational exposure limit (OEL). Results: The substances most frequently measured were nickel (insoluble), followed by sulfuric acid, lead, chromium (VI), formaldehyde, phenol, dimethylformamide and benzene. The industries with highest number of measurement samples for special management substances were plating of metals, followed by hospitals, general repair services of motor vehicles, building of ships, manufacture of synthetic resin and other plastic materials, manufacture of finished medicaments. Out of the 37 special management substances studied, 22 had a non-detection rate of over 90%. The rate of samples exceeding the OEL was less than 1% for all substances. The substance with the highest number of samples exceeding the OEL was trichloroethylene, which also had the highest average concentration compared to exposure limit. The substances with the highest percentage of industries which (X_0.95) exceeding OEL was formaldehyde followed by sulfuric acid, trichloroethylene, lead, I-bromopropane etc. Conclusions: This study identified high-risk industries of CMR sunstances, highlighting the need for prioritizing these industries in hazards surveillance and risk assessment.