• Journal of Mechanical Science and Technology
• /
• v.16 no.6
• /
• pp.799-809
• /
• 2002

In order to utilize a parallel mechanism as a machine tool component, it is important to estimate the errors of its end-effector due to the uncertainties in parts. This study proposes an error analysis for a new parallel device, a cubic parallel mechanism. For the parallel device, we consider two kinds of errors. One is a static error due to link stiffness and the other is a dynamic error due to clearances in the parts. In this study, we propose a stiffness model for the cubic parallel mechanism under the assumption that the link stiffness is a linear function of the link length. Also, from the fact that the errors of u-joints and spherical joints are changed with the direction of force acting on the link, they are regarded as a part of link errors, and then the error model is derived using forward kinematics. Lastly, both the error models are integrated into the total error, which is analyzed with a test example that the platform moves along a circular path. This analysis can be used in predicting the accuracy of other parallel devices.

• Journal of the Korean Society for Heat Treatment
• /
• v.15 no.3
• /
• pp.118-126
• /
• 2002

TiCN thin films were deposited on tool steels at $510^{\circ}C$ by PECVD from a $TiCl_4+N_2+CH_4+H_2+Ar$ gaseous mixture. The microstructures and preferred orientation were investigated. The micro-scratch tests were performed using a system equipped with an acoustic emission sensor. Critical loads were determined to evaluate the adhesion of TiCN to substrate. The influences of the microstructures of substrates, double layered coatings, and coatings after nitriding(duplex coating) were investigated. The experimental results showed that the microstructures of substrates and double layered coating did not affect the critical loads considerably. By the duplex coating, critical loads were not always increased. In some cases, duplex coatings decreased critical loads significantly despite of absence of black layer. In this study, we tried to relate the results of scratch test to the residual stress analysis. Nitriding before the coating reduces the tensile residual stress in the film, which gives rise to low critical load in scratch test.

• Korean Journal of Materials Research
• /
• v.27 no.11
• /
• pp.636-642
• /
• 2017

In the present study the microstructure of low-carbon steels fabricated by controlled rolling and accelerated cooling processes was characterized and identified based on various microstructure analysis methods including optical and scanning electron microscopy, and electron backscatter diffraction(EBSD). Although low-carbon steels are usually composed of ${\alpha}-ferrite$ and cementite($Fe_3C$) phases, they can have complex microstructures consisting of ferrites with different size, morphology, and dislocation density, and secondary phases dependent on rolling and accelerated cooling conditions. The microstructure of low-carbon steels investigated in this study was basically classified into polygonal ferrite, acicular ferrite, granular bainite, and bainitic ferrite based on the inverse pole figure, image quality, grain boundary, kernel average misorientation(KAM), and grain orientation spread(GOS) maps, obtained from EBSD analysis. From these results, it can be said that the EBSD analysis provides a valuable tool to identify and quantify the complex microstructure of low-carbon steels fabricated by controlled rolling and accelerated cooling processes.

• Korean Journal of Computational Design and Engineering
• /
• v.11 no.3
• /
• pp.223-233
• /
• 2006

Layered manufacturing(LM) is emerging as a new technology that enables the fabrication of three dimensional heterogeneous objects such as Multi-materials and Functionally Gradient Materials (FGMs). Among various types of heterogeneous objects, more attention has recently paid on the fabrication of FGMs because of their potentials in engineering applications. The necessary steps for LM fabrication of FGMs include representation and process planning of material information inside an FGM. This paper introduces a new process planning algorithm that takes into account the processing of material information. The detailed tasks are discretization (i.e., decomposition-based approximation of volume fraction), orientation (build direction selection), and adaptive slicing of heterogeneous objects. In particular, this paper focuses on the discretization process that converts all of the material information inside an FGM into material features like geometric features. It is thus possible to choose an optimal build direction among various pre-selected ones by approximately estimating build time. This is because total build time depends on the complexity of features. This discretization process also allows adaptive slicing of heterogeneous objects to minimize surface finish and material composition error. In addition, tool path planning can be simplified into fill pattern generation. Specific examples are shown to illustrate the overall procedure.

• Journal of the Korean Society for Precision Engineering
• /
• v.15 no.2
• /
• pp.154-161
• /
• 1998

Prototypes of a design are always needed for the purpose of visualization and evaluation in the aspect of manufacturability functionality, and aesthetic appearance. Since the prototyping process requires a significant amount of cost and time, various rapid prototyping processes are recently being introduced in the process. However, it is usually necessary for a part built up by a rapid prototyping system to be refined by a post-processing process, in which the stair steps on the surfaces, the support structures (if they exist), and the unprocessed material are eliminated. This post-processing is usually done manually and is a time-consuming task. Especially, eliminating the trapped volumes, the volume of the unprocessed material entrapped by the solidified portion, is sometimes impossible in some processes. This study provides a designer with a tool to detect the existence and to calculate the quantity of the trapped volumes at the given build-up direction, so that the proper build-up direction is chosen or the part is built by pieces to avoid the problems caused by the trapped volumes in advance. Since the proposed algorithm can efficiently calculate the amount of the trapped volumes at any build-up direction, it has the potential of such application as optimizing the build-up direction to minimize the trapped volumes.

• Journal of Korean Clinical Nursing Research
• /
• v.21 no.2
• /
• pp.252-265
• /
• 2015

Purpose: This study examined the circumstances, risk factors, and the predictors of fall incidents among patients in the small and medium-sized hospitals. Methods: Fifty patients with any fall experiences were matched by gender, age, and medical departments with 100 patients without fall incident at the same hospital. Data were collected from 5 small and medium-sized hospitals. Data were analyzed using descriptive statistics, a Chi-square test, a Fisher's exact test, and a logistic regression with the SPSS/WIN 21.0 program. Results: In the patients with falls, the largest number of falls occurred during the day shift, in the patients' rooms, and while they were walking. Further 74.0% of the patients had physical injuries, and 34.0% had to take further medical diagnostic tests. Significant differences were found between the patients with falls and the others on 14 variables (cardiovascular disease, anemia, sedative-hypnotics, vasodilators, narcotic analgesics, dizziness, general weakness, unstable gait, walking aids, anger, anxiety, depression, orientation, and fear of fall). Narcotic analgesic use, dizziness, walking aids, and cardiovascular disease were identified as the predictors of fall incidents. Conclusion: These findings are hoped to be used in developing a fall risk assessment tool and fall prevention nursing programs for small and medium-sized hospitals.

• Proceedings of the Korean Operations and Management Science Society Conference
• /
• 2006.05a
• /
• pp.348-353
• /
• 2006

Autonomous and intelligent resource model (AIR-model) defines a building-block of complex systems to pursue value creation by means of diverse resources, referred to as an AIR-unit, and presents a collaboration model with the AIR-units. An AIR-unit represents a piece of resources, such as machines, labor, raw materials, and other assets, considered individually by a complex system as means to accomplish given tasks. It is defined with its own service capability and a goal, and pursues achieving the goal by means of the capability. Moreover, an Air-unit is equipped with autonomy and intelligence, whereby it makes a decision on its course of action on its own initiative. Air-units collaborate on system operations with each other through goal-oriented negotiations. In this research, distinctive features of the AIR-model are addressed and described in detail. Principal components of the AIR-model are also designed via object-oriented modeling techniques. A prototype system based on the AIR-model is finally presented as an embodiment tool of a fractal manufacturing system (FrMS).

• International Journal of CAD/CAM
• /
• v.3 no.1_2
• /
• pp.85-95
• /
• 2003

During the design of dies and molds, the cavity of the object is obtained by subtracting it from a surrounding rectangular block. This box is subsequently split into two halves by the parting surface. Similar problems also occur in some RP processes such as LOM, SGC, SLS and 3DP where the machine produces a block inside which the prototype is buried. Determining the orientation of the object inside the box and the corresponding parting surface taking appropriate constraints into account have been addressed by several researchers. However, given the parting surface, the problem of splitting the box development of a software package called OptiLOM (now a module of an RP software Magics 8.0), the authors realized non-triviality of this problem since the loop can spread over as many as 5 faces of the box. In this paper, the authors have tried to bring out the importance of this problem and have presented their algorithm to solve it.

• Fashion & Textile Research Journal
• /
• v.16 no.2
• /
• pp.218-227
• /
• 2014

In this study, we ran a collage fashion illustration program. We used in depth personal interviews to find if there are any change in self-image by psychologically analyzing the features of self-images expressed in the pieces of fashion illustration. The total number of objects were five females students majoring in fashion design in Busan. They were hoping to have a psychology consultation to resolve their concerns about the future, family affairs, appearance, and careers. Collage fashion illustration program was used as a experimental tool to find the psychological features shown in the formats and content of collage fashion illustration. We then figure out how pre and post diagnosis were different from each other in terms of ego-identity and DAP. As a result, the formats in collage fashion illustration are related to the self images such as psychological energy, incompetency, suppression, and tendency of self-centered. Also, the contents of the fashion expression are related to the self-images such as dependency, avoidance, wariness, and self-regard. All of the participants have improved self-regard and active action due to improvements in subjectivity, initiative, and goal orientation. Therefore, they could change from pessimistic self-images to optimistic ones.

• Transactions of the Korean Society of Machine Tool Engineers
• /
• v.15 no.6
• /
• pp.1-7
• /
• 2006

This paper presents the study in the development of optimal working method for an outer-hull preprocessing robot using a quaternion. The out-hull preprocessing robot consists of feathering and cleaning parts. This robot should be controlled correctly for feathering work because it is to be worked on a curved plate that can result in the errors of orientation. In this paper, we propose a control algorithm between given two orientations of the out-hull preprocessing robot by using a quaternion with spherical linear interpolation. The proposed control algorithm is shown to be effective in terms of motor angles and torques when compared to a conventional Euler angle interpolation, by using both $MATLAB^{\circledR}$ and $VisualNastran4D^{\circledR}$.