• The Journal of Korea Robotics Society
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• v.11 no.2
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• pp.73-82
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• 2016

This paper focuses on the vibration analysis of planar cable-driven parallel robots on their configurations. Despite of many advantages of the cable robots, elasticity of the cables may cause the vibration at the existence of external disturbance, resulting in deterioration of positioning accuracy. According to the vibration theory, having high first order natural frequency can prevent resonance with low frequency disturbance from the surrounding environment. A series of simulations showed that choosing frame / end-effector shape and cable connection method affects robots' natural frequency. For the precise simulation, the cables are modeled as linear springs and axial vibration of cables is mainly considered. Aspect ratios of the frame and end-effector are defined as non-dimensional parameters while their areas are fixed. It was shown that vibration analysis guides to design a planar cable robot in terms of high capacity to reduce vibration.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1997.04a
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• pp.551-556
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• 1997

Based on the experiment for the frequency characteristics and the feedback theory of the impinging-tones, the unstable characteristics of the symmetric mode is analyzed among the various unstable modes of circular impinging jets. There are two different symmetric modes; one is the low-frequency mode S1 due to the vortex at the outside of the jet and the high-frequency mode S2 due to the inside vortex. Each mode has its own characterictics of convection speed decreasing with frequency.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.22 no.12
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• pp.1227-1236
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• 2012

The low speed machinery faults are usually caused by the bearing failure of the rolling elements. As the life time of the bearing is limited, the condition monitoring of bearing is very important to maintain the continuous operation without failures. A few monitoring techniques using time domain, frequency domain and fuzzy neural network vibration analysis are introduced to detect and diagnose the faults of the low speed machinery. This paper presents a method of fault detection for the rolling element bearing in the low speed machinery using the Wiener filtering and shock pulse counting techniques. Wiener filter is used for noise cancellation and it clearly makes the shock pulse emerge from the time signal with the high level of noise. The shock pulse counting is used to determine the various faults obviously from the shock signal with transient pulses not related with the bearing fault. Machine fault simulator is used for the experimental measurement in order to verify this technique is the powerful tool for the low speed machine compared with the frequency analysis. The test results show that the method proposed is very effective parameter even for the signal with high contaminated noise, speed variation and very low energy. The presented method shows the optimal tool for the condition monitoring purpose to detect the various bearing fault with high accuracy.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.19 no.10
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• pp.1028-1033
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• 2009

To detect faults and monitor thinning on a pipe, many people use ultra sonic sensors that are operated in high frequency range. Because there are many modes in high frequency range, it is difficult to find faults and monitor pipe thinning on a structure. If we deal with signals in a low frequency range which include only A0 wave and S0 wave, the information of monitoring and diagnosis can be easily obtained. In this paper, the technique for exciting low frequency range using ultra sonic sensors is proposed. The main idea of the proposed method comes from the beat phenomenon. The beat frequency is equal to the absolute value of the difference in frequency of the two waves. If the beat frequency is tuned by two ultra waves, we can excite A0 mode and S0 mode of structures. To verify the proposed method, we have performed a steel plate and pipe experiments. Experimental results show that two ultra sonic sensors can well excite low frequency range.

• Journal of KSNVE
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• v.10 no.6
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• pp.991-997
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• 2000

The objective of this study is to examine the onset condition and the frequency characteristics of the low-frequency combustion oscillation in a surface burner. For this purpose, extensive parametric studies have been performed experimentally and the effects of size of each section, the equivalence ratio, and the entrance velocity on oscillatory behavior explored. The experimental results were discussed in comparison with the other combustors associated tilth the low-frequency combustion oscillation. The combustion mode is driven at high combustion rate by the lift of unstable flame near the lower limit of the combustible equivalence ratio. The oscillation frequency is dependent not on the burner geometry but on the equivalence ratio and the combustion load. Low-frequency combustion mode was formed to be divided into two different modes, named C1 and C2 respectively. Two modes occurred individually, simultaneously or transitionally according to the equivalence ratio and combustion load. The characteristics of low-frequency oscillation is different from each other depending on the type of combustors. The surface burner has also its own characteristics of low -frequency oscillation.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.18 no.7
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• pp.756-763
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• 2008

This paper presents an inchworm with three piezoelectric actuators. The dynamic stiffness of the inchworm is generally low compared to its driving condition, so mechanical vibration may degenerate the motion accuracy of the inchworm. The dynamic model of inchworm is identified by curve fitting technique based on the experimental frequency response function. For the precision motion control and low residual vibration of inchworm, driving input signal is designed by using cycloid step input and LQG control technique. Experimental result shows that proposed input shaping method is applicable effectively to the inchworm.

• Proceedings of the KSR Conference
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• 2008.11b
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• pp.1607-1613
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• 2008

The present investigate is a base investigate required in development of DMT wagon train. And it deduced that follows by developing trail analysis model about Modalohr wagon train and examining traveling movement specific using analysis model developed. Vibration acceleration of all direction was increased with addition of travel speed and first suspension. But in case of right and left vibration acceleration, that could influenced by nonlinear specific of first suspension. Therefore checking about those is needed. Frequency of $2{\sim}3\;Hz$ and $7{\sim}8\;Hz$ generated in Right and left, up, down vibration of vehicle. And right and left vibration of bogie generated $25{\sim}35\;Hz$ in low speed section and frequency of $40{\sim}50\;Hz$ in high speed section, $25{\sim}35\;Hz$ in low speed section, $10{\sim}15$ or $40{\sim}50\;Hz$ in high speed section.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.20 no.12
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• pp.1128-1138
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• 2010

One of the typical problems in the precise vibration is resonance characteristics at low frequency disturbance due to a heavy mass. An electro-magnetic(EM) air spring is a kind of vibration control unit and active isolator. The EM air spring in this study aims at removing the low frequency resonance for semiconductor manufacturing. The mechanical and electronic parts in the active isolator are designed to operate under a weight of 2.5 tons. The EM spring is floated using air pressure in a pneumatic elastic chamber and actuated by EM levitation force. The actuator consists of a EM coil and a permanent magnetic plate which are installed inside of the chamber. An air mount was constructed for the experiment with a stone surface plate, 4 active air springs, 4 gap sensors, a DSP controller, and a multi-channel power amp. A PD control method and operating logic was applied to the DSP. Simulation using 1/4 model was carried out and compared with the experiments. The time duration and maximum peak at resonance frequency can be reduced sharply by the proposed system. The results show that the active system can avoid the resonance caused by the natural frequency of the passive system.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.05a
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• pp.194-201
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• 2001

The dynamic characteristic of the building using preflex composite beams is a low natural frequency due to long span. Therefore, both vibrational acceleration and the characteristic of natural frequency damage to people using the building, This study estimates a vibrational acceleration based on walking and natural frequency in five kinds of building. Recently, using methods of evaluating a serviceability are based on JIA, AISC, Eurocode, CSA, DIN and ISO. ed. The result of this study is content with foreign regulations and serviceability. However, considering of these results, the method of evaluating serviceability should be developed in the future.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.11a
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• pp.390-393
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• 2005

In this study, examined heavy-weight floor impact sound to rahmen structure(steel reinforced concrete structure) and bearing-wall structure(box frame type structure) that have slab thickness of 4 form at a standard laboratory through noise and vibration measured. The results of ANSYS modeling of structures was predicted that the nature natural frequency increased according to change of thickness of each slab by finite element analysis, and acceleration value decreased. Rahmen structures compares with bearing-wall structure, nature frequency was predicted low. Measurement results of natural frequency and acceleration level for structures at a standard laboratory, tendency department such as ANSYS modeling appeared. Rahmen structures appeared that reduction effect is less in Acceleration level and heavy impact sound transmission level comparing with bearing-wall structure.