• Structural Engineering and Mechanics
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• v.72 no.5
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• pp.557-568
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• 2019

Accurate modeling of contact interface in bolted joints is crucial in predicting the dynamic behavior for bolted assemblies under external load. This paper presents a contact pressure distribution based non-uniform virtual material method to describe the joint interface of assembly structure, which is connected by sparsely distributed multi-bolts. Firstly, the contact pressure distribution of bolted joints is obtained by the nonlinear static analysis in the finite element software ANSYS. The contact surface around bolt hole is divided into several sub-layers, and contact pressure in each sub-layer is thought to be evenly. Then, considering multi-asperity contact at the micro perspective, the relationship between contact pressure and interfacial virtual material parameters for each sub-layer is established by using the fractal contact theory. Finally, an experimental platform for the dynamic characteristics testing of a beam lap structure with double-bolted joint is constructed to validate the efficiency of proposed method. It is found that the theoretical results are in good agreement with experimental results by impact response in both time- and frequency-domain, and the relative errors of the first four natural frequencies are less than 1%. Furthermore, the presented model is used to examine the effect of rough contact surface on dynamic characteristics of bolted joint.

• Journal of the Korean Society for Precision Engineering
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• v.33 no.8
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• pp.669-681
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• 2016

Mechanical designers often make mistakes that result in unwanted over-constraints, causing difficulty in assembly operations and residual stress due to interference among parts. This study is concerned with detection and elimination of over-constraints. Screw theory is a general method that is used for constraint analysis of an assembly and motion analysis of a mechanism. Mechanical assemblies with plane-plane, pin-hole, and pin-slot constraint pairs are analyzed using screw theory to illustrate its utility. As a real-world problem, a ball valve design is analyzed using the same method, and several unwanted over-constraints are detected. Elimination measures are proposed. Nominal dimensions of some parts are adjusted, and dimensions and tolerances of the pins and holes are modified using the virtual condition boundary concept. The revised design is free of over-constraints. General procedure for applying screw theory to constraint analysis is established and demonstrated; it will contribute to improving quality of assembly designs.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.16 no.2
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• pp.78-83
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• 2007

In this paper, the digital model of the micro-factory has been established, inspected and evaluated by progress of assembly, manipulation and examination. The new paradigm of the system analysis is realized by digital simulation of the factory. The digital manufacturing system of the micro-factory was simulated through UML(Unified Modeling Language) with the object-oriented logical model analysis method and then the micro lens module assembly system was simulated with MST(Micro System Technology) Application Module.

• Journal of Korean Physical Therapy Science
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• v.24 no.1
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• pp.59-68
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• 2017

Purpose : The aims of this study was to conduct a systematic literature review with meta-analysis to investigate the effect of virtual reality based rehabilitation program on balance of patient with stroke in Korean studies. Method : The studies for analysis were searched in electronic databases(Research Information Sharing Service; RISS, Korean Studies Information Service; KISS, DBpia, e-articles, National Assembly Library). The key words for search were 'virtual reality', 'stroke', and 'balance' and only randomized controlled trials and clinical controlled trials were included. Of 40 studies identified in the search, 20 studies met the criteria of this study and included in this meta-analysis. Result : The results were as follows: 1) The overall effect size of virtual reality based rehabilitation program was 0.557(95% critical interval; 0.340~0.774). 2) In the analysis of sub-categorical variables, effect size was as follows; the commercial game type(0.621) > virtual environment type(0.335); the dynamic balance measurement(0.750) > static balance measurement(0.226); randomized controlled trial(0.653) > clinical controlled trial(0.275); and thesis type(0.706) > article of journal type(0.339). 3) In the analysis of sub-continuous variables, as time of program(per session) increased, the balance increased(p<0.05). Conclusion : The results of this study showed that virtual reality based rehabilitation program moderately improves the balance of stroke patient. Further studies are recommended to investigate the effect of sub-variables related to virtual reality programs on motor functions of patient with stroke.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.16 no.1
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• pp.124-133
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• 2017

In the current lighting market, LEDs that have a high luminous efficiency, a long life and consume less power have emerged as next generation lighting. Owing to various designs and sizes of LEDs, the production process of existing LEDs involves many tasks that require manual labor; hence, the assembly of LEDs necessitates manpower. Because of the use of manpower, the production costs of LEDs increases and production efficiency decreases. Recently, the assembly parts of LEDs have been standardized for minimizing manual labor, and an LED is developed as an LED panel. The automatic assembly system produces LED convergent lighting by assembling two LED panels and one diffusion cover. To increase the production efficiency of the LED convergent lighting module, it is important that the development of a feeder can continuously supply the LED panels is required, and whose design has sufficient stability. The automatic assembly system of the LED convergent lighting module consists of two feeders, which convey LED panels and diffusion covers to a main conveyor, which assembles the lifted panels and covers. In this study, structural analysis and fatigue life for forced loads on the conveyer line of the feeder in the process of lifting LED panels and diffusion covers of each feeder, is analyzed. In addition, the drive of the belt constituting the conveyor line of each feeder is simulated, and the dynamic characteristics of the belt is analyzed using the virtual engineering method.

• Journal of Korea Multimedia Society
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• v.8 no.12
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• pp.1658-1668
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• 2005

This paper presents the bytecode-to-SIL translator which enables the execution of the java program in EVM(Embedded Virtual Machine) environment without JVM(java Virtual Machine), translating bytecodes produced by compiling java programs into SIL(Standard Intermediate Language) codes. EVM, what we are now developing, is a virtual machine solution that can download and execute dynamic application programs written in sequential languages like C language as well as object oriented languages such as C#, Java, etc. EVM is a virtual machine mounted on embedded systems such as mobile device, set-top box, or digital TV, and converts the application program into SIL, an assembly language symbolic form, and execute it. SIL is a virtual machine code for embedded systems, based on the analysis of existing virtual machine codes such as bytecode, MSIL, etc. SIL has such features as to accommodate various programming languages, and in particularly has an operation code set to accept both object-oriented languages and sequential languages. After compiling, a program written in java language is converted to bytecode, and also executed by JVM platform but not in other platform such as .NET, EVM platform. For this reason, we designed and implemented the bytecode-to-SIL translator system for programs written in java language to be executed in the EVM platform without JVM. This work improves the execution speed of programs, enhances the productivity, and provides an environment for programmers to execute application programs at various platforms.

• Korean Journal of Computational Design and Engineering
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• v.14 no.4
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• pp.242-253
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• 2009

Nowadays, manufacturing industry has been making its effort not only for productivity elevation but also for cost reduction in order to survive in the global market which is more and more challenging. In this paper, the method for planning of digital manufacturing system is proposed and door trim assembly system is determined as the subject of our research. First of all, the process sequence is generated based on the product analysis. And, the static and dynamic relationships between system components are represented using IDEF0 and UML model. The working time is estimated through the regression analysis based on MODAPTS method. According to the system configuration strategy, initial concept system layout is implemented 3D virtual environment. The problems caused by bad working motions are detected and modified through the ergonomic analysis using RULA method. According to proposed procedure, digital door trim assembly system is implemented in DLEMIA.

• Proceedings of the Safety Management and Science Conference
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• 2002.05a
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• pp.99-103
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• 2002

It is the basic requirement of product characteristics to specify geometric dimensions and tolerances during design process of parts assembly. Therefore, there are many tolerance stack analysis method to explain tolerance zone. Tolerance stack analysis is to calculate gap using tolerances which includes geometric and coordinate dimension. In this study, we compared several different stack analysis method and try to suggest more general method called the Virtual Method to analyze tolerance stack.

• Korean Journal of Computational Design and Engineering
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• v.13 no.1
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• pp.36-44
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• 2008

This paper proposes a modeling and simulation process of a panel production line (PPL) in a shipyard. The panel production line is an assembly process to produce a main panel of a flat block and a curved block. In this paper, its activity analysis is carried out using expression of IDEF0, and its process is qualitatively and quantitatively analyzed and modeled by Petri Nets. A commercial discrete event simulation tool, $QUEST^{TM}$, is used for virtual PPL and simulation. The modeling results by Petri Net are mapped to elements of the simulation tool. Finally, an integrated simulation environment of PPL is implemented in order to efficiently utilize the virtual PPL model. With the help of IDEF0 and Petri Nets, we could systematically analyze and describe the PPL process that are characterized as being concurrent, asynchronous, distributed, parallel, nondeterministic, and/or stochastic. Also, the dynamic and concurrent activities of a PPL system were able to be simulated. A timing concept can be included into the Petri nets model to evaluate performance and dependability issues of the system.

• Journal of Digital Convergence
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• v.11 no.4
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• pp.273-278
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• 2013

This paper simulated the virtual constructions design that helps make constructions design effectively done by assembling materials as components and patterns using studs in steel house method. We also propose the virtual constructions design technology which makes change of constructing easy and reduces the cost effectively through a simulation of construction design like design, analysis, change information, and assembly in the construction field. It especially is possible for designers and users to change internal and external of a construction easily by using patterns.