• 영어어문교육
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• 제17권4호
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• pp.75-95
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• 2011

The purpose of this study was to evaluate a group activity, reciprocal peer tutoring (RPT), in order to investigate advantages and challenges of RPT in promoting cooperative and collaborative learning environment for EFL University reading instruction. The participants in this study were 89 students taking an English reading course at a Korean university. RPT is a learning strategy whereby learners help each other and learn by teaching. This program was supported by a Vygotskyan perspective which assumes that learners gain mastery and develop cognitive skills through social interaction with more proficient others and their environment. This study relied particularly on participant perceptions through questionnaire survey and Anonymous Online class Report of the course. This study showed various advantages for tutors such as learning through teaching and becoming more autonomous and responsible for their own learning. Non-threatening and highly motivating learning atmosphere are parts of benefits for tutees. Other advantages for tutees included improved level of academic self-confidence, and motivation. This study also revealed several drawbacks associated with the problem of inaccuracy in students' production and students' demand for more direct teacher role. (182 words).

• 동력기계공학회지
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• 제12권6호
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• pp.78-82
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• 2008

Plastic gears are more and more widely used in many industrial machine elements. Plastic gear has higher properties such as light weight, wear resistance, and vibration absorbing ability than metallic gears. But, in case of using an inaccurate plastic gear, its tooth breakage happen and fatigue life is shortened due to increase of applying load and temperature rising on the tooth flank. Inaccuracy of plastic gears such as pitch circle roundness and tooth profile generates vibration and noise. In this study, an internal plastic gears which is molded by a new injection mold structure are developed. The new mold structure is called the HR3P(hot runner type 3plate mold) that has an improved runner system in order to have good filling balance. As a result from this study, an internal gear with very accurate roundness was developed by using design of experiment.

• 한국정밀공학회지
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• 제23권4호
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• pp.168-175
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• 2006

This paper presents surface matching algorithms that can be used to reconstruct the surface topography of an object scanned by an AFM. The essence of the algorithms is to match up neighboring images intentionally overlapped with others. Two performance indexes using the correlation coefficient and the sum of the squared differences are introduced. To compensate for the inaccuracy of the coarse stage implemented to AFM, all the six axes including the rotational degrees of freedom are successively matched so as to maximize the coefficients defined. The results show that the proposed algorithms are useful for measurement range extension of AFM. The results also show that a combined use of the two indexes is beneficial for practical cases.

• International Journal of Precision Engineering and Manufacturing
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• 제3권1호
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• pp.49-56
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• 2002

The Z-map is a special farm of discrete non-parametric representation in which the height values at grid points on the xy-plane are stored as a 2D array z[ij]. While the z-map is the simplest farm of representing sculptured surfaces and is the most versatile scheme for modeling non-parametric objects, its practical application in industry (eg, tool-path generation) has aroused much controversy over its weaknesses, namely its inaccuracy, singularity (eg, vertical wall), and some excessive storage needs. Much research or the application of the z-map can be found in various articles, however, research on the systematic analysis of sculptured surface shape representation via the z-map model is rather rare. Presented in this paper are the following: shape modeling power of the simple z-map model, exact (within tolerance) z-map representation of sculptured surfaces which have some feature-shapes such as vertical-walls and real sharp-edges by adopting some complementary z-map models, and some application examples.

• International Journal of Precision Engineering and Manufacturing
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• 제1권2호
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• pp.115-123
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• 2000

We propose an extended version of multi-step algorithm of self-calibration of interferometric optical testing instruments. The key idea is to take wavefront measurements with near equal steps in that a slight angular offset is intentionally provided in part rotation. This generalized algorithm adopts least squares technique to determine the true azimuthal positions of part rotation and consequently eliminates calibration errors caused by rotation inaccuracy. In addition, the required numbers of part rotation is greatly reduced when higher order spatial frequency terms are of particular importance.

• 한국정밀공학회지
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• 제20권10호
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• pp.226-232
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• 2003

Difficulties in the finite element modeling of human spine are evaded by using a stiffness matrix element whose properties can be characterized from experimentally measured stiffness of functional spinal units. Relative easiness is in that inter-vertebral discs, ligaments, and soft tissues connecting vertebrae do not need to be modeled as they are. The remarkable coupling effect between distinct degrees of freedom induced by the geometric complexity can be accommodated without much effort. An idealized block model with simple geometry for vertebra is employed to assess the feasibility of this method. Analyses are performed in both levels of motion segment and spinal column, and the result is compared with that from detail model. As far as the global behavior of spine is concerned, the simplification is found not to aggravate inaccuracy only if sufficient experimental data is provided and interpreted properly.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1999년도 제3회 압연심포지엄 논문집 압연기술의 미래개척 (Exploitation of Future Rolling Technologies)
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• pp.88-97
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• 1999

In this study, a systematic approach for roll pass design in bar rolling was studied. To minimize the trial and errors in the process design, a roll CAD system and a FE analysis system were combined. Based on the system, a methodology for roll pass design by FEM was studied. At first, designed process was compared with the FE analysis results and process redesign based on the FEM results was performed to obtain the specified final geometry. Then, empirical formula for roll speed set-up was compared with the FE analysis results. Further study on various simulations for bar rolling will help in making up for the inaccuracy in the currently used empirical roll speed rules. In addition, verification of the accuracy of the FE analysis system must be performed using experimental data in the industry.

• Journal of Welding and Joining
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• 제22권2호
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• pp.46-50
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• 2004

In today's highly competitive marketplace, it is of great significance for the manufacturing industry to reduce lead-time and costs fur the product development. Since first emerged in 1986, Rapid Prototyping (RP) technology has helped successfully to reduce time and costs. Recently, RP using functional materials such as metal has been researched. However RP using the molten metal has been struggling to resolve several drawbacks, such as dimensional inaccuracy, poor surface finish, post finishing, etc., that originate primarily from the overall deposition of molten metal for each layer. So, the purpose of this study is to develop a new RP technique using sheet metal and projection welding for reducing several drawbacks in occurring RP using molten metal. Also tensile and bending specimens were made by the developed RP process using projection welding and were verified.

• 제어로봇시스템학회논문지
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• 제4권4호
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• pp.420-426
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• 1998

It is the purpose of this paper to make a preliminary study on the use of repetitive control to improve velocity accuracy by eliminating repetitive disturbances caused by machining inaccuracies of the axis of rotation location. If the control system can be intelligent enough to compensate for such machining errors, then one may be able to improve the accuracy of the velocity control, or alternatively, one may maintain the same accuracy and relax the machining tolerances required. This could decrease cost significantly. Experiments are performed testing repetitive control methods on a constant speed rolling operation testbed. The experimental results show very substantial decreases in the tracking error of the system. Spectral data of the output motion are given to demonstrate the attenuation of the disturbance frequencies and harmonics, related to the bandwidth being used. It is seen that the simplest form of repetitive control which is very easily implemented, can produce striking improvement in control system performance in such belt drive rolling operations, and the learning can be accomplished in a short time.

• Composites Research
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• 제13권5호
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• pp.44-49
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• 2000

Although the net-shape molding of composites is generally recommended, molded composites frequently requires cutting or grinding due to the dimensional inaccuracy for precision machine elements. The surface roughness and cutting force were also measured to investigate the surface grinding characteristics of the composites using the vitrified bonded wheel (WA, GC). The experiments were performed dry grinding conditions with respect to cutting speed, feed speed, depth of cut of the stacking sequence $[O]_{nT.}$ From the experimental investigation, the optimal conditions both the vitrified bonded wheel WA and GC for the surface grinding are suggested.