• 제어로봇시스템학회:학술대회논문집
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• 1988.10b
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• pp.869-874
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• 1988

The operational control of the rotary snowplow is considered to improve its working efficiency. The speed of the rotary snowplow is controlled, so that the load to the rotary snowplow is kept constant. As the load can not directly be detected, some items considered for the controlled variable are, for example, the engine revolution, the load pressure and etc. In order to examine these, the working simulation of the rotary snowplow was considered by introducing the experimental equation of the load. The control methods were examined by means of the simple digital control using the personal computer. These control methods were compared with simulations and experiments. Consequently, the working efficiency is improved about 20% than the manual operation.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.18 no.6
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• pp.9-18
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• 2019

This study derives load characteristics and analyzes the safety of plowshares operating in dry fields. We mounted a three-blade, reversible plow on a 23.7 kW tractor and measured the plow's tractive force as well as the torque from the engine output shaft on the rear axle under various working speeds (L4, M1, M2, M3). We chose a Korean test site of Seomyeon, Chuncheon with sandy soil texture, as determined using the USDA method. We constructed the load spectrum for torque and tractive force using measured data and derived the fatigue life of the plowshare from a stress-cycle (S-N) curve of the plow material. Our results show that the M3 gear maximizes the driving shaft torque loads and, applying the tractive force load spectrum, creates a cumulative damage sum of $4.14{\times}10^{-5}$. Considering sampling time, we estimate a fatigue life of 805 hours while using the M3 gear. When using the other working speeds, however, all of the stress levels fell within the endurance limits and, therefore, our model predicts infinite plowshare lifetimes. For this analysis, we used a yield strength of 1,079 MPa for the plowshare and static safety factors, analyzed using the maximum stress, between 6.83 and 8.63 under each working speed.

• Educational Technology International
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• v.10 no.2
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• pp.145-166
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• 2009

The purpose of this study was to investigate why advance organizers (AO) are effective in promoting comprehension and mental model formation in terms of cognitive load. Two experimental groups: a concept-map AO group and a key-word AO group and one control group were used. This study considered cognitive load in view of Baddeley's working memory model: central executive (CE), phonological loop (PL), and visuo-spatial sketch pad (VSSP). The present experiment directly examined cognitive load using dual task methodology. The results were as follows: central executive (CE) suppression task achievement for the concept map AO group was higher than the key word AO group and control group. Comprehension and mental model construction for the concept map AO group were higher than the other groups. These results indicated that the superiority of concept map AO owing to CE load decrement occurred with comprehension and mental model construction in learning. Thus, the available resources produced by CE load reduction may have been invested for comprehension and mental model construction of learning contents.

• Korean Journal of Occupational Health Nursing
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• v.11 no.2
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• pp.121-131
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• 2002

Objective: The purpose of this study was to determine the physical load by identifying harmfully working postures and to develop recommendations for improving the existing situation with nurses in ICU, thereby to provide the basis for development of work-related musculoskeletal preventive program. Method: Various types of tasks were recorded with a video camera to chart and analyze different postures by OWAS(Ovako Working Posture Analysing System). Collected data showed that poor postures were adopted, not only for lifting or repositoning a patient, but also for other tasks. Data Analysis: The performed activities were then divided into Nursing Intervention Classification. Altogether 128 postures were selected for analysis. Then they were classified into different OAC (OWAS Action Categories). From all the observation, unhealthy postures, for which corrective measures had to be considered immediately (i.e., 75% classified as OACII+III+IV) were found. Collected data were analyzed in terms of percentage, 2-tail Mann-Whitney U test. Result: Poor postures mainly occur during 'positioning the patient' and 'airway suctioning' in NIC. No difference was found (p=0.060) between the percentage of harmful posture adopted during the patient handling tasks and non-patient handling tasks. Conclusion: This study shows, that in the nursing profession with ICU not only occur during patient handling, but also during other activities. The OWAS method was useful in determining the physical load by locating potential activities due to harmfully working postures, providing a detailed description with analysis, and suggesting successful means to reduce postural load.

• Wind and Structures
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• v.19 no.1
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• pp.1-14
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• 2014

Rail-mounted cranes can be easily damaged by a sudden gust of wind while working at a running speed, due to the large mass and high barycenter positions. In current designs, working rail-mounted cranes mainly depend on wheel braking torques to resist large wind load. Regular brakes, however, cannot satisfactorily stop the crane, which induces safety issues of cranes and hence leads to frequent crane accidents, especially in sudden gusts of wind. Therefore, it is necessary and important to study the braking performance of working rail mounted cranes under wind load. In this study, a simplified mechanical model was built to simulate the working rail mounted gantry crane, and dynamic analysis of the model was carried out to deduce braking performance equations that reflect the qualitative relations among braking time, braking distance, wind load, and braking torque. It was shown that, under constant braking torque, there existed inflection points on the curves of braking time and distance versus windforce. Both the braking time and the distance increased sharply when wind load exceeded the inflection point value, referred to as the threshold windforce. The braking performance of a 300 ton shipbuilding gantry crane was modeled and analyzed using multibody dynamics software ADAMS. The simulation results were fitted by quadratic curves to show the changes of braking time and distance versus windforce under various mount of braking torques. The threshold windforce could be obtained theoretically by taking derivative of fitted curves. Based on the fitted functional relationship between threshold windforce and braking torque, theoretical basis are provided to ensure a safe and rational design for crane wind-resistant braking systems.

• Proceedings of the KIEE Conference
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• 1999.11b
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• pp.276-278
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• 1999

In this paper, we analyze customers' working electric energy (kWh) which is served pole-transformer in order to reduce peak load current error which is generated in application load correlation equation. The characteristic of electric load which customers are using is classified by customer's working electric energy (kWh) and ratio of cooling equipment possession. For the input data of fuzzy model, we used to kWh on April which represents basic load and kWh which is increased from April to August. The April kWh is used to classify into large, medium, small customer. Also, the increased kWh is used to know information of cooling equipment possession. For the output value of fuzzy model, we can determined peak load current limit in application load correlation equation.

• Proceedings of the KIEE Conference
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• 1999.07c
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• pp.1267-1269
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• 1999

This paper studies on arrangement of load correlation coefficient for advanced load management. To accurate load correlation coefficient, we used two real factors, electrical energy(kWh) and peak load current of pole transformers, acquired by measuring instrument. Out of several correlation equations, we find that the quadratic equation is the most accurate to express peak load current and working electrical energy. If the data is located in the outside of ${\pm}3{\sigma}$ it is discarded. For load management, we rearranged load correlation coefficient considering +2${\sigma}$ at load correlation equation. Comparing conventional load correlation coefficient with rearranged one, we can get the result of error reduced and it is adjacent to the actual data. It will be used peak load forecasting from working electrical energy and we are able to prevent from the damaging of pole transformer due to overload.

• Geomechanics and Engineering
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• v.20 no.5
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• pp.447-459
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• 2020

Based on the literature statistical method, the paper publication status of the isolated working face and the distribution of the rockburst coal mine were obtained. The numerical simulation method is used to study the stress distribution law of working face under different mining range. In addition, based on the similar material simulation test, the overlying strata failure modes and the deformation characteristics of coal pillars during the mining process of the isolated working face with thick-hard key strata are analyzed. The research shows that, under the influence of the key strata, the overlying strata formation above the isolated working face is a long arm T-type spatial structure. With the mining of the isolated working face, a series of damages occur in the coal pillars, causing the key strata to break and inducing the rockburst occurs. Combined with the mechanism of rockburst induced by the dynamic and static combined load, the source of dynamic and static load on the isolated working face is analyzed, and the rockburst monitoring methods and the prevention and control measures are proposed. Through the above research, the occurrence probability of rockburst can be effectively reduced, which is of great significance for the safe mining of deep coal mines.

• Journal of the Korean Society of Safety
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• v.14 no.4
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• pp.192-198
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• 1999

Work-related musculoskeletal disorders constitute a major source of employee disability and lost wages. Cumulative Trauma Disorders(CTD) refers to a category of physical conditions which result from chronic musculoskeletal injury. Assessment of CTD risk in industry at early stage allows for early control, a safe environment, and a healthier workforce. In this study, the physical load of the shipping work in the cold storage warehouse were especially investigated. Employees were working with almost unnatural posture in a very restricted work space. The questionnaire and biomechanical analysis were used to evaluate the physical load. Results from analyses showed that they were sufficiently exposed to CTD due to repetition and unnatural posture. Based on the analysis, ways for improving working conditions are proposed. The analysis and proposals in this paper will serve as a basic tool for designing/redesigning working environment such as improvement of tools and equipments, design of times for work/rest cycle.

• Proceedings of the KSME Conference
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• 2007.05a
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• pp.820-825
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• 2007

A ballscrew-linear motion(LM) guide is well-described by its name: it is a LM guide that runs by ballscrew. It consists of LM rail, LM block, end plate, screw, nut and bearing balls. The ballscrew-LM guide has many advantages compared with conventional LM guide. The high efficiency achieved with rolling contact devices permits the employment of antibacklash methods. The balls provide the only physical contact between nut rail and block and ball screw and nut replacing the sliding friction with a rolling motion. The life of the ballscrew-LM is determinated by the balls. The objective of this paper is to introduce the design of the ballscrew-LM with the safety working load.