• Journal of the Korean Society of Manufacturing Process Engineers
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• v.11 no.5
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• pp.142-147
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• 2012

Machining tool conditions directly affect to quality of product and productivity of manufacturing. Many researches performed for tool condition monitoring in machining process to improve quality and productivity. Conventional methods use characteristics of signal for cutting force, motor current consumption, vibration of machine tools and machining sound. Recently, diameter of machining tool is become smaller for minimizing of mechanical parts. Tool condition monitoring using conventional methods are relatively difficult because micro machining using small diameter tool has low machining load and high cutting speed. These days, the direct monitoring for tool conditions using vision system is performed actively. But, vision system is affected by external conditions such as back ground of image and illumination. In this study, minimizing technology of external conditions using distribution analysis of image data are developed in micro machining using small diameter drill and tap. The image data is gathered from vision system. Several sets of experiment results are performed to verify the characteristics of the proposed machining technology.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.12 no.6
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• pp.22-28
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• 2003

We should maintain the maximum operation capacity for production facilities and find properly out the fault of each equipment rapidly in order to decrease a loss caused by its failure. The acoustic signals of a machine always carry the dynamic information of the machine. These signals are very useful for the feature extraction and fault diagnosis. We performed a fundamental study which develops a system of fault diagnosis for a pump. We obtained noises by a microphone, analysed and compared the signals converted to Sequency range for normal products, artificially deformed products. We tried to search a change of noise signals according to machine malfunctions and analyse the type of deformation or failure. The results showed that acoustic signals as well as vibration signals can be used as a simple method for a detection of machine malfunction or fault diagnosis.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.10a
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• pp.547-550
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• 1997

The dynamic behavior of rotor-bearing system has been investigated using finite element method. A procedure is presented for dynamic modeling of rotor-bearing system which consist of shaft elements, rigid disk, flexible bearing and support structures. A finite element model including the effects of rotary inertia, shear deformation, gyroscopic moments is developed. Linear stiffness and damping coefficient are calculated for 3 lobe sleeve bearing. The whirl frequency, mode shape, stability and unbalance response of rotor system included effect of bearing coefficient and support structures are calculated.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2003.04a
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• pp.99-104
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• 2003

We should maintain the minimum operation capacity for production facilities and find properly out the fault of each equipment rapidly in order to decrease a loss caused by its failure. The acoustic signals of a machine always carry the dynamic information of the machine. These signals are very useful for the feature extraction and fault diagnosis. We performed a fundamental study which develops a system of fault diagnosis for a pump. We obtained noises by a microphone, analysed and compared the signals converted to frequency range for normal products, artificially deformed products. We tried to search a change of noise signals according to machine malfunctions and analyse the type of deformation or failure. The results showed that acoustic signals as well as vibration signals can be used as a simple method for a detection of machine malfunction or fault diagnosis.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.17 no.6
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• pp.124-131
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• 2008

There are many factors which affect the acoustical properties of a micro-speaker. Among the factors, the shape of the diaphragm is considered in this study. As an investigating method, the finite element methods and measurement techniques applied to study the acoustical properties according to diaphragm shape. In order to vary the stiffness of the diaphragm, the some patterns of comb teeth, such as the angle and the number of comb teeth, are applied to diaphragm. We can confirm that the change of the stiffness by the changing diaphragm shape affects the vibration and sound properties of the speaker. As a result, the reduction of the angle of the comb teeth increases the diaphragm stiffness and shifts the resonance frequency to a higher frequency range. The number of the comb teeth is related to the stiffness of the edge part.

• Journal of KSNVE
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• v.8 no.1
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• pp.187-194
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• 1998

In order to predict the train noise propagation from a level railroad, this paper presents the model of train noise source and the prediction model based on the results by using the sound intensity method. The prediction model gives the effects of geometric attenuation, ground attenuation, and barrier attenuation of noise. There are several principal assumption in developing model: (a) the train noise is primarily rolling noise; (b) the rail head and wheels are in good condition; (c) the height of source is 10cm above track; (d) the directivity pattern of train noise sources is a dipole source. Calculated results based on this model are compared with available field data and good agreement has been obtained.

• Journal of KSNVE
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• v.6 no.6
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• pp.835-842
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• 1996

To identify the locations and strengths of acoustic sources, one may use a microphone line array. Apparent advantage of the source identification method utilizing a line array is that it requires less measurement points than intensity method and holography. This method is based on the information of magnitude and phase difference between pressure signals at each microphone. Since those differences are dependent on the source model, we have to assume them such as plane, monopole, etc. In this paper the conventional source identification methods such as beamforming method and MUSIC method are briefly reviewed by modeling a source as plane and spherical wave, then a modified method is introduced. This can be applied to sound field which may by either coherent or incoherent. Typical simulations and experiment are performed to confirm this identification method.

• Explosives and Blasting
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• v.21 no.1
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• pp.49-58
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• 2003

현재 발파의 수행은 채석, 채굴 및 지하철과 도로, 건축, 토목공사 등 다양한 분야에 적용되고 있다. 이에 따라 발파특성의 연구와 관련하여 다양한 이론이 도출되고 있고 사용되지만 발파에 의한 공해인 진동 및 소음의 문제가 대두되면서 또한 이들의 취약점을 보완하기 위해 다양한 공법들이 시행되고 개선되어지고 있다. 본 연구에서는 기존의 발파공법과 Air tubes를 이용한 발파공법을 비교하므로 화약의 사용량을 보다 감소시키고, 기존 전색의 길이를 줄이므로 폭약의 투사면적을 증대시켜 진동 및 폭음을 감소시키고 상대적으로 양호한 파쇄입도를 얻고 상부의 대괴를 최소화하는데 목적이 있다. 따라서 발생하는 진동 및 발파폭음을 크게 감소시킬 수 있으므로 기존 노천발파 및 진동, 소음에 민감한 도심지 발파에서 그 이점을 활용하여 보다 안전적이고 경제적인 발파작업을 수행하는데 연구의 목적이 있다.

• Explosives and Blasting
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• v.21 no.3
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• pp.17-22
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• 2003

발파작업에서 발생하는 공해로 인한 재산상의 피해나 정신적인 피해를 최소화하기 위하여 대부분의 현장에서 제어발파를 시행하고 있다. 이완식 제어발파는 발파의 규모가 일반발파와 비교하여 작고, 대상 구조물이 근거리에 위치하므로 그 전달특성이 다를 수 있다. 근거리에서 계측된 발파진동의 특징은 고주파이고 진동의 지속시간이 짧다. 본 연구는 국내의 8개 지역에서 계측한 자료를 분석하여 이완식 제어발파의 진동전달 특성에 관하여 국내의 현장에서 시공 전에 진동을 추정할 수 있는 진동전파식을 제안하였다. 또한 제어발파시에 사용하는 폐타이어를 부착한 철재매트에 의한 폭풍압의 저감 효과와 전달특성을 분석하였다.

• Journal of KSNVE
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• v.9 no.1
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• pp.113-120
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• 1999

A perforated tube nozzle as an exhaust noise suppressor of a high-speed civil transport(HSCT) is proposed. The experimental results for the near and far field sound. the visualization of jet structures and the static pressure distributions in the jet passing through a perforated tube are presented and discussed in comparison with those for a simple tube. It is shown that the perforated tube has an excellent performance to greatly reduce the shock-associated noise and that also the turbulent mixing noise is reduced in the range of a limited jet pressure ratio. This considerable noise reduction is due to the pressure relief caused by the through-flow through the perforated holes. Such a pressure relief results in the transformation of normal shock waves into weak Mach waves of X -type and increases the thrust force of the perforated tube nozzle.