Kihong Shin

Machinery Fault Diagnosis Using Two-Channel Analysis Method Based on Fictitious System Frequency Response Function

Most existing techniques for machinery health monitoring that utilize measured vibration signals usually require measurement points to be as close as possible to the expected fault components of interest. This is particularly important for implementing condition-based maintenance since the incipient fault signal power may be too small to be detected if a sensor is located further away from the fault source. However, a measurement sensor is often not attached to the ideal point due to geometric or environmental restrictions. In such a case, many of the conventional diagnostic techniques may not be successfully applicable. In this paper, a two-channel analysis method is proposed to overcome such difficulty. It uses two vibration signals simultaneously measured at arbitrary points in a machine. The proposed method is described theoretically by introducing a fictitious system frequency response function. It is then verified experimentally for bearing fault detection. The results show that the suggested method may be a good alternative when ideal points for measurement sensors are not readily available.

Comparative Study on the Measures of Similarity for the Location Template Matching(LTM) Method

The location template matching (LTM) method is a technique of identifying an impact location on a structure, and requires a certain measure of similarity between two time signals. In general, the correlation coefficient is widely used as the measure of similarity, while the group delay based method is recently proposed to improve the accuracy of the impact localization. Another possible measure is the frequency response assurance criterion (FRAC), though this has not been applied yet. In this paper, these three different measures of similarity are examined comparatively by using experimental data in order to understand the properties of these measures of similarity. The comparative study shows that the correlation coefficient and the FRAC give almost the same information while the group delay based method gives the shape oriented information that is best suitable for the location template matching method.

Identification of Multiple Impacts on a Plate Using the Time-Frequency Analysis and the Kalman Filter

This article presents the method of identifying the locations of the multiple impacts on a plate where the impacts occur sequentially. The main aim of this research is to provide the basis on the human-interaction technology using variety of methods used in the area of signal processing, piezoelectric materials, and wave propagation. The work concerning the location identification of a single impact on a plate has been previously studied by means of the time-frequency analysis applied to accelerometer signals. In this article, a novel approach for the location identification of the discrete multiple impacts is presented to investigate the feasibility of applying to a more practical human-interaction system. For the identification of the series of impact locations, the major axisymmetry mode of the Lamb wave on the plate is considered and the CWT is applied to obtain the arrival time difference of the Lamb waves between sensors. Then, the Kalman filtering technique is employed to continuously track the locations of the impact load and to improve the estimation results. The results may well be applied to the real-time health monitoring of the steam generator in a nuclear power plant.

Development of a Low-Cost Steering System Simulator

The Steering system is the most important system for a vehicle, in terms of safety and driving feel. But in many cases, experiments to improve the steering feel using a real vehicle are very difficult in the aspects of repeatability, safety and money. Repeatability in testing steering systems is very important because the steering feel for a driver varies according to the environmental conditions. In addition to that, steering tests using vehicle are so dangerous that the driver might not concentrate on the tests. In this paper, a new steering system simulator using the front part of a steering and suspension system is described. This simulator allows cheap, safe, and repeatable testing of the steering system compared with the real vehicle test.

Design Parameter Study on the Isolation Performance of the HSLDS Magnetic Vibration Isolator

In general, the softer the stiffness of a linear vibration isolator the better the performance of isolation can be achieved. However, the stiffness of the isolator cannot be made too soft because it needs a sufficient stiffness to hold the load. This is the most critical limitation of a linear vibration isolator. Recently, a HSLDS(high-static-low-dynamic-stiffness) magnetic vibration isolator was proposed to overcome this fundamental limitation. The suggested isolator utilizes two pairs of attracting magnets that introduces negative stiffness. Previously, this new type of vibration isolator was merely introduced and showed a possibility of practical use. In this paper, detailed dynamics of the HSLDS magnetic isolator are studied using computer simulations. Then, the isolation performance is examined for various design parameters to aid the practical use.

The Effect of the Number of Vibration Modes on the Application of the Location Template Matching(LTM) Method

ABSTRACT The location template matching (LTM) method is a technique of identifying an impact location on a structure, and is often applied to structural health monitoring and large scale human-computer inter-face (HCI) systems. The LTM method utilizes a certain measure of similarity between two time signals. The correlation coefficient is most widely used for this purpose, and the group delay based method is recently proposed to improve the accuracy of finding the best matching pair of signals. In practice, one of key essential consideration for implementing the LTM method is to guarantee that a sufficient number of vibration modes must be contained in the measured signal, and yet the lower sampling rate is needed for a real-time implementation. In this paper, the properties of correlation coefficient and group delay with respect to the number of vibration modes are investigated. A few important results are obtained through extensive computer simulations and experiments. If the number of vibration modes contained in the measured signal is more than four it is sufficient for the corre-lation based LTM method, while the group delay based LTM method requires smaller number of vi-bration modes.

Source Location of Multiple Impacts on the Plate Based on Pre-signal Processing

This paper presents the novel work for source localization of serial multiple impacts in a plate sructure. It is difficult to identify the source of serial multiple impacts with the current source localization techenology(SLT) because of the overlapping of dispersive wave induced by multiple impacts and the reflaction from the edge of the plate. In this paper, the new method is suggested for source localization. The method is developed based on the SLT with pre-signal processing such as some limitation for the selection of three sensors, the frequency range for TFA and impact time interval. Results from numerical simulation and experiment in isotropic plate structure are presented, which show the capability of the proposed method.

Experimental Evaluation of the Performance of the HSLDS Magnetic Vibration Isolator with Consideration of the Design Parameter

The isolation performance of a linear vibration isolator is limited to the ratio of stiffness to mass it supports. The stiffness of the isolator must be large enough to hold the weight. This results in the deterioration of the isolation performance. Recently, to overcome this fundamental limitation, the HSLDS(high-static-low-dynamic-stiffness) magnetic vibration isolator was introduced and its isolation characteristic was investigated theoretically. In this paper, the isolation performance of the HSLDS magnetic isolator is examined experimentally. Considerable amount of experiments are performed by carefully considering nonlinear characteristics. The experimental results verify the practical usability promisingly and agree with the theoretical studies, i.e. its performance is largely dependent on the key design parameter.

Piezoceramic cantilever sensor design for weak-impact detection on plates

A piezoelectric cantilever type sensor for locating the precise weak-impact or touch position on a plate is presented in this paper. Since the importance of human-computer interface such as a touch panel system has been rapidly increasing recently, this study could suggest an appropriate sensor for the detection of a weak-impact point effectively and accurately for such a system. This sensor detects the out-of-plane vibration of a panel when a touch with a finger or pen is applied on it. The sensor is made with a steel beam and a single crystal PMN-PT patch is bonded on the beam, which is designed to detect the base vibration of the panel. The sensor was designed, manufactured to verify the detect ability of a weak-impact and attached on two different plates of a glass of 400 × 400 × 4 mm and a wooden MDF of 600 × 600 × 9 mm. The experiment result of the sensor was compared with that of an accelerometer which can also be used for the same purpose and shows clear weak-impact responses with a narrow-band property at its resonant frequency. It is expected that the cantilever type sensor in this study could be applied to make a simple flat plate into a touch panel when the time difference of arrivals method is used to locate the weak-impact point.

Multi Impact Identification Base Kalman Filter

The aim of this paper is to present the method of identifying the impact location on the plate. This basic research has the purpose to achieve the human-interaction technology based on the signal processing, piezoelectric materials, and wave propagation. The work concerning the location identification of a single impact on the plate has been previously studied by means of the time frequency analysis applied to accelerometer signals. In this paper, a novel approach for the location identification of the discrete impact is presented to investigate the feasibility of applying to a human-interaction system. For the identification of the impact location, the major axisymmetry mode of the Lamb wave on the plate is used for this work and Kalman filter tracking is employed.Copyright