• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.16 no.3
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• pp.276-283
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• 2006

Work-related musculoskeletal disorders (WMSDs) were a major source of disability and lost work time after 'Foreign Currency Crisis(1998-2000)' in Korea. There is considerable evidence documenting the association between psychosocial risk factors and work disability due to WMSDs. But, there is not much in Korea. The present study aimed to explore the predictive association between the changed working conditions and WMSDs after 'Foreign Currency Crisis' in Korea. A study sample of 8,670 automobile assembly workers were recruited for this study. A structured-questionnaire was used to assess general characteristics, working conditions, and information concerning medical treatment of WMSDs. After adjustment for sociodemographic factors, increased overtime work(OR=1.22), daily work time(OR=1.20), work speed (OR=1.32), number of workers(OR=0.83), supervisory control(OR=1.39), physical load(OR=1.39), and mental load (OR=1.25) were all founded to be significantly associated with WMSDs. This study has shown the importance of changed working conditions in the occurrence of WMSDs. Therefore, it will be necessary to reduce WMSDs with controlling both physical and psychosocial factors.

• Industrial Engineering and Management Systems
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• v.10 no.3
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• pp.197-202
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• 2011

In traditional production lines, such as assembly lines, each worker is usually assigned to a particular fixed work, and decreasing the task to master the assigned work is valuated. However, when an imbalance exists between workers' speeds, if a worker delays the overall work in the production line, the production rate of the particular line will also decrease. To avoid this problem, the "Self-Balancing Production Line" was introduced. In this type of production line, each worker is assigned work dynamically, and when specific conditions are satisfied, production remains balanced. Characteristics of these lines that can be preempted at any place have already been analyzed by some researchers. A previous paper examined the situation in which only a single worker can process one machine and cannot preempt processing, and the improved policy of an ordinary selfbalancing production line, which specifies which stations workers can process and how workers can behave. This policy achieveda high production rate with only four stations and two workers (Buzacott, 2002). In that paper, worker processing stations and the behavior of a specific worker were limited, andthe paper focused only on specific stations and workers. Therefore, it is not applicable to any worker sequence. In this paper, we focus on other ways to decrease cycle time. In this kind of line, a worker processes at his or her speed. Therefore, if a worker is assigned stations according to his or her speed, the line can decrease cycle time. To do so, we relax the assumptions of this type of line and set a new condition. Under these conditions, we compare our results to the results of previous papers.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.18 no.7
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• pp.56-62
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• 2019

The high-precision laser scriber carries out scribing alumina ceramic substrates for manufacturing ultra-small chip resistors. The ceramic substrates are loaded, aligned, scribed, transferred, and unloaded. The entire process is fully automated, thereby minimizing the scribing cycle time of the ceramic substrates and improving the throughput. The scriber consists of the laser optical system, pick-up module of ceramic substrates, pre-alignment module, TH axis drive work table, automation module for substrate loading / unloading, and high-speed scribing control S/W. The loader / unloader unit, which has the greatest influence on the scribing cycle time of the substrates, carries the substrates to the work table that carries out the cutting line work by driving the X and Y axes as well as by adsorbing the ceramic substrates. The loader / unloader unit consists of the magazine up / down part, X-axis drive part for conveying the substrates to the left and right direction, and the vision part for detecting the edge of the substrate for the primary pre-alignment of the substrates. In this paper, the laser scribing machining simulation is performed by applying the instrument mechanism of each component module. Through this study, the scribing machining process is first verified by analyzing the process operation and work area of each module in advance. In addition, the scribing machining process is optimized by comparing and analyzing the scribing cycle time of one ceramic substrate according to the alignment stage module speed.

• Journal of the Korea Institute of Building Construction
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• v.23 no.4
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• pp.429-440
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• 2023

This research investigates the deployment of waterproofing technologies in construction, with a specific focus on augmenting worker safety, work environment, and solve the difficulty of securing skilled workers. Implementing liquid waterproofing cement equipment resulted in a remarkable increase in adhesion performance by around 20%, coupled with a twofold acceleration in operational speed. The application of primer spraying apparatus led to a two-fold improvement in both penetration and adhesion performance, concurrently boosting the work speed by approximately the same factor. With urethane spraying equipment, the workload could be reduced to a third for the same layer thickness, adhesion performance enhanced by approximately 1.4 times, and workability improved by about 1.4 to 1.5 times. These findings suggest that such technological interventions can potentially enhance work efficiency, improve the quality of output, and mitigate safety accidents that are commonplace in manual operations. Furthermore, these advancements present promising solutions to the ongoing challenges of sourcing highly-competent workers in the industry.

• The Journal of the Convergence on Culture Technology
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• v.9 no.4
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• pp.569-576
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• 2023

An agricultural drones are gradually increasing in utilization due to economic efficiency, and consist of a main frame in charge of flying spray system in charge of moving pesticide to control targets. Therefore, the environment and characteristics of crops should be considered when controlling pesticides using drones and conditions such as systematic flying altitude of flight, speed, and spray time should be changed accordingly. However, pest control work using agricultural drones has different spray effects depending on level the operation proficiency and spray impact. In addition, there are variations in operating standards and control efficiency for agricultural drones, which hinder the distribution of agricultural control drones in the field of pest control work. Therefore, this study attempts to identify the spraying characteristics of agricultural drones, apply the effective spraying time, interval and experimentally verify the system that can calculation of spray area compared to previous studies. Through this experimental verification, it is intended to apply the optimal control process by minimizing the obstacles to pest control work by applying the operation method and systematic figures to agricultural drones.

• Tribology and Lubricants
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• v.33 no.5
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• pp.220-227
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• 2017

In this work, carbon nanotube and nano-size alumina particle are exploited as additive for lubrication experiment. We used pin-on-disk type tribometer to investigate the tribological characteristics of lubricants with respect to additives and rotational speed. We conducted more than 15 trials of tribotests for two hours for each specimen to obtain stable and accurate frictional force and to create measurable wear track on the substrate. We conducted tests at the boundary/mixed lubrication regime to evaluate the influence of additives on the tribological characteristics. We found that the friction coefficient decreased as the rotational speed increased and as additives were added. In particular, the reduction of friction by adding additives was more significant at low rotational speed than at high rotational speed. We speculate that the additives helped to separate and protect the two contacting surfaces at low speed, while the influence of additives was not significant at high speed since sufficiently thick lubricant film was formed. The wear of the substrate was also reduced by adding additives to the lubricant. However, in contrast to friction, the amount of wear at high rotational speed was less when alumina particles were added to the lubricant than the amount of wear at low speed. We speculate that the increased wear at low rotational speed is as a result of the intermittent abrasive wear caused by alumina particles with uneven shape, while the reduced wear at high speed is as a result of sufficient film thickness which prevented the abrasive wear.

• Journal of Power System Engineering
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• v.21 no.5
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• pp.86-91
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• 2017

Friction Stir Welding (FSW) is useful technique to join aluminum alloy with energy efficient and environment friendly. In this paper, the design of experiment with three-way factorial design was adopted for optimum conditions of welding variables in the FSW of Al 6061 alloy. Tools of shoulder diameter of 9, 12, 15 mm and pin length of 1.5 mm were used. Also the material's dimension for welding were $2{\times}100{\times}150mm$, and the tensile specimens were worked by water-jet technique. Welding variables were shoulder diameter, rotating speed and travel speed of tool. From the results of this work, the welding factor influenced on yield strength most was travel speed and the optimum condition for FSW was predicted as the shoulder diameter of 15 mm, welding speed of 500 mm/min and rotating speed of 2,000 rpm. Also the presumption range of yield strength at optimal condition of reliability 99% was estimated to $207.19{\pm}9.91MPa$.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2002.04a
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• pp.32-37
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• 2002

High speed machining is one of most effective technologies to improve productivity. It can give great advantage for manufacture of die and Moulds. However, when the high speed machining of materials, especially in machining of micro groove, a severely thermal demage was generated on workpiece and tool. Generally, the cutting fluid is used to improve penetration, lubrication, and cooling effect. In order to rise the performance of lubrication, it contains extreme pressure agents (Cl, S, P). But the environment of work room go bad by those additive Therefore, the compressed chilly air with Oil mist system was developed to replace the conventional cutting fluid system. This paper carried out the tests to evaluate the machinability by the cutting environment in high speed micro groove machining of NAK80 (HRC40). Compressed chilly air with oil mist was ejected on the contact area between cutting edge and workpiece. The effectiveness of this developed compressed chilly air with oil mist system was evaluated in terms of tool life. The results showed that the tool life of carbide tool coated TiAIN with compressed chilly air mist cooling was much longer than with dry and flood coolant when cutting the material.

• Journal of Korean Society for Atmospheric Environment
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• v.14 no.6
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• pp.607-620
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• 1998

The influence of transportation on air quality has been elevating in urban area. Air pollutants from automobiles cause primary and secondary air pollution, and need to be tightly controlled. In this study, the effect of automobile air pollutants on highway vicinity area was evaluated by the comparison of field measurement. and target was for modeling using CALINE3, NO2 was the target for this work. It was found that the concentration predicted by CALINE3 is overestimated at low wind speed and input data of wind speed requires correction. Based on the measured data, the wind speed was modified by effective wind speed equation [Ue=U+0.24·EXP(-pxU)], and there after the accuracy of CALINE3 calculation was improved neighborhood area of highway. It was also observed that weather conditions and traffic volume affect the concentration of air pollution. Finally, the NO2 effect of automobile air pollutants on the vicinity area of highway proved to be up to 400∼600m from the highway.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.3B
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• pp.85-94
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• 2005

In this paper, we propose a reliable high-speed UDP-based media transport with an adaptive error control. The proposed adaptive transport scheme controls the amount of redundancy by monitoring the network in order to adapt to network fluctuations efficiently. The feedback of receiver enables the sender to be aware of current reception status (i.e., rate and type of packet loss) and to estimate the expected network status. Based on this, the proposed transport attempts to enable reliable transport by adaptively controlling the amount of both whole sending rate and the ratio for adaptive FEC code. Experiment with high-speed network has been conducted to verify the performance of the proposed system that demonstrates the enhanced reliability of the proposed transport at the speed of up to several hundred Mbps.