• 한국정밀공학회지
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• 제23권6호
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• pp.111-118
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• 2006

Recently, the reliability evaluation and analysis are applied far many industrial products which are required to guarantee in quality and efficiency. The purpose of this paper is to present some of reliability evaluation methodologies that are applicable to machine tools. Especially ATC (Automatic Tool Changer), which is a core component of line center, was chosen as the target of the reliability evaluation and analysis. The scope of research is reliability prediction, reliability test and evaluates their results. The results of reliability evaluation have shown the failure rates, MTBF (Mean Time Between Failure), reliability for those components of ATC and real tests reliability through the constructed reliability test-bed. It is expected that proposed methodologies would increase reliability for a high-speed line center.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2001년도 춘계학술대회 논문집
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• pp.59-62
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• 2001

Reliability engineering is regarded as the major and important roll for all industry. And advanced manufacturing systems with high speed and intelligent have been developing for the betterment of machining ability. In this study, we have systemized evaluation of reliability for machinery system. We proposed the reliability assessment and design review method using analyzing critical units of high speed and intelligent machine system. In addition, we have not only designed and developed test bed system for acquiring reliability data, but also apply QFD technique for satisfying quality function which is provided in design phase. From this study, we will expect to guide and introduce the reliability engineering in developing and processing phase of high quality product.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1997년도 추계학술대회 논문집
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• pp.43-46
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• 1997

Reliability engineering is regarded as the major and important roll for all industry. And advanced manufacturing systems with high sped and intelligent have been developing for betterment of machining ability. In this study, we have systemized evaluation of reliability for machinery system. We proposed the reliability assessment and designed and manufactured reliability test-bed to evaluate reliability. In addition we acquired reliability data using test-bed system and made database to handle reliability data. And also we not only use reliability data by analyzing reliability, but also apply design review method using analyzing critical units of machinery system. Form this study, we will expect to guide and increase the reliability engineering in developing and processing phase of high quality product.

• 산업경영시스템학회지
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• 제28권1호
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• pp.49-54
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• 2005

Recently, the reliability are applied for many industrial products, and many products are required to guarantee in quality and in performance. The purpose of this paper is to present some of reliability prediction methodologies using failure rate database for machinery parts that are applicable to machine tools. VDI Turret, which is core component of the NC Lathe, was chosen as the target of the reliability prediction. The results of reliability prediction has shown the failure rate, MTBF(Mean Time Between Failure), and reliability of the VDI Turret. It is expected that proposed methodologies will be applicable to prediction of reliability for other components of machine tools.

• 대한전기학회논문지
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• 제39권3호
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• pp.301-311
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• 1990

A multiple controller structure consisting of a typical feedback controller and an additive redundant controller is proposed for enhancing the reliability of the control system. For the case where the main controller is chosen as a pole assignment controller with input/output measurements and the redundant controller as the Model Reference Adaptive Controller (MRAC) whose reference model is the closed-loop combination of the plant and the main controller, it is proven that the tracking error between the command input and plant output converges to zero under failure in one of the controllers or parameter perturbations of the plant, and further that the reliability measured by Mean Time To Failure (MTTF) is greater than that of the system with only a single main controller. A simulation Example is provided to illustrate reliable operation of the proposed control system against the controller failure.

• 산업경영시스템학회지
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• 제40권1호
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• pp.165-172
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• 2017

Machines are physically or chemically degenerated by continuous usage. One of the results of this degeneration is the process mean shift. Under the process mean shift, production cost, failure cost and quality loss function cost are increasing continuously. Therefore a periodic preventive resetting the process is necessary. We suppose that the wear level is observable. In this case, process mean shift problem has similar characteristics to the maintenance policy model. In the previous studies, process mean shift problem has been studied in several fields such as 'Tool wear limit', 'Canning Process' and 'Quality Loss Function' separately or partially integrated form. This paper proposes an integrated cost model which involves production cost by the material, failure cost by the nonconforming items, quality loss function cost by the deviation between the quality characteristics from the target value and resetting the process cost. We expand this process mean shift problem a little more by dealing the process variance as a function, not a constant value. We suggested a multiplier function model to the process variance according to the analysis result with practical data. We adopted two-side specification to our model. The initial process mean is generally set somewhat above the lower specification. The objective function is total integrated costs per unit wear and independent variables are wear limit and initial setting process mean. The optimum is derived from numerical analysis because the integral form of the objective function is not possible. A numerical example is presented.

• Archives of Reconstructive Microsurgery
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• 제24권1호
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• pp.1-6
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• 2015

Purpose: The main cause of flap loss in microsurgical tissue transfer is venous insufficiency. Whether or not multiple venous anastomoses prevents vascular thrombosis and reduces the risk of flap failure remains controversial. Some researchers are in favor of performing dual venous anastomoses, but the counterargument holds that performing a single venous anastomosis does provide advantages. Materials and Methods: We carried out a retrospective analysis of 15 cases of anterolateral thigh free flap for extremity reconstruction performed between January 2011 and December 2013. The patients were categorized into two groups: group A that received a single venous anastomosis and group B that received dual venous anastomoses. The time of the anastomosis, size of the flap, complications of the flap, and survival rate of each group were analyzed. Results: The total microsurgical time in the single venous anastomosis group ranged from 28 to 43 minutes (mean 35.9 minutes). The total time in the dual anastomoses group ranged from 50 to 64 minutes (mean 55.7 minutes). No statistically significant difference was found between the two groups with regards to postoperative complications and flap failure. Conclusion: Our study suggests that the use of a single venous anastomosis in the venous drainage of anterolateral thigh free flaps is a safe and feasible option for extremity reconstruction and provides shorter operative time and easy flap dissection.

• 한국간담췌외과학회지
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• 제27권3호
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• pp.271-276
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• 2023

Backgrounds/Aims: Laparoscopic cholecystectomy within one week of acute cholecystitis is considered safe and advantageous. Surgery beyond first week is reserved for non-resolving attack or complications. To compare clinical outcomes of patients undergoing laparoscopic cholecystectomy in the first week and between two to six weeks of an attack of acute cholecystitis. Methods: In an analysis of a prospectively maintained database, all patients who underwent laparoscopic cholecystectomy for acute cholecystitis were divided into two groups: group A, operated within one week; and group B, operated between two to six weeks of an attack. Main variables studied were mean operative time, conversion to open cholecystectomy, morbidity profile, and duration of hospital stay. Results: A total of 116 patients (74 in group A and 42 in group B) were included. Mean interval between onset of symptoms & surgery was five days (range, 1-7 days) in group A and 12 days (range, 8-20 days) in group B. Operative time and incidence of subtotal cholecystectomy were higher in group B (statistically not significant). Mean postoperative stay was 2 days in group A and 3 days in group B. Laparoscopy was converted to open cholecystectomy in two patients in each group. There was no incidence of biliary injury. One patient in group B died during the postoperative period due to continued sepsis and multiorgan failure. Conclusions: In tertiary care setting, with adequate surgical expertise, laparoscopic cholecystectomy can be safely performed in patients with acute cholecystitis irrespective of the time of presentation.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2004년도 추계학술대회 논문집
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• pp.539-544
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• 2004

In this paper, we present reliability modeling and analysis method of the Automated Guideway Transit(AGT) vehicle system using analytical models, based on Markov Chains. The Markov model can express state transition of the AGT vehicle sys. that is considered to be in one of four states, such as basic operating (0), minor delay(1), major delay(2) and non-operating(3) state. The proposed Markov model is illustrated with a numerical example and cases to find a steady state availability, MTBF(mean time between failures), and MTTR(mean time to repair) under specified failure and repair rate arc demonstrated.

• 한국군사과학기술학회지
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• 제13권1호
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• pp.41-49
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• 2010

In this paper, we propose a hierarchical RAM simulation model framework which are used to analyze the RAM specifications on the concept refinement phase. The hierarchical RAM simulation model framework consists of RAM simulation models, class library and each model's input and output data lists. The hierarchical RAM simulation models are co-operated with 3 kinds of model - type I, II, III. Type I, II models are used to analyze the target operational availability and Type III is used to establish the initial RAM specifications. Each model's input and output data lists are defined by considering each model's purpose of RAM analysis. The class library is arranged with each model's classes for implementing the hierarchical simulation models. The proposed framework may be applied for executing the RAM activities effectively.