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이선표 ( Sunpyo Lee ) 한국센서학회 2018 센서학회지 Vol.27 No.4
A Wi-Fi signal network (WSN) system is introduced in this paper. This system consists of several data-transmitting sensor modules and a data-receiving server. Each sensor module and the server contain a unique intranet IP address. A piezoelectric accelerometer with a bandwidth of 12 kHz, a 24-bit analog-digital converter with a sampling rate of 15.625 kS/s, a 32-bit microprocessor unit, and a 1-Mbps Wi-Fi module are used in the data-transmitting sensor module. A 300-Mbps router and a PC are used in the server. The system is verified using an accelerometer calibrator. The voltage output from the sensor is converted into 24-bit digital data and transmitted via the Wi-Fi module. These data are received by a Wi-Fi router connected to a PC. The input frequencies of the accelerometer calibrator (320 Hz, 640 Hz, and 1280 Hz) are used in the data transfer verification. The received data are compared to the data retrieved directly from the analog-to-digital converter used in the sensor module. The comparison shows that the developed system represents the original data considerably well. Theoretically, the system can acquire vibration signals from 600 sensor modules at an accelerometer bandwidth of 15.625 kHz. However, delay exists owing to software processes, multiplexing between sensor modules, and the use of non-real time operating system. Hence, it is recommended that this system may be used to acquire vibration signals with up to 10 kHz, which is approximately 70% of the theoretical maximum speed of the system. The system can be upgraded using parts with higher performance
김인응(InWoong Kim),이선표(SunPyo Lee),최현(Hyun Choi) 한국소음진동공학회 2014 한국소음진동공학회 학술대회논문집 Vol.2014 No.10
The chatter vibration in the machining process plays bad role in machining quality such as high roughness as well as tool life and machine failure. And the grinding process under this risk in the fully automated factory is exposed to the unexpected mass machining quality problem. Studying the vibration signal of the hub bearing grinding process, the reason of chatter vibration was explained with the specific machining pattern of chatter. And this study suggests the chatter detecting method in the production line, which is monitoring the peak acceleration level around the natural frequencies of the specimen, and calculating kurtosis value by assuming the chatter is related to the resonance of the specimen. The suggested method was applied to the vehicle hub bearing grinding process and proved good to detecting the chatter induced machining quality problem.
민옥기,이선표 연세대학교 산업기술연구소 1988 논문집 Vol.20 No.2
In this paper, the accuracy, convergency and efficiency of the time integral schemes which determine the viscoplastic (creep) strain rate occuring in an incremental elasto-viscoplastic finite element analysis are compared and discussed. Forward, central and backward difference schemes are employed in the temporal domain and the isoparametric 2-D quadrilateral elements are used in the spatial domain. The viscoelastic Maxwell material is incorporated with the elasto -plastic idealization in order to model the visco-plastic constitutive relation. A homogeneous function is used in the fluidity parameter. Total Lagrangian formulation is adopted for the larger displacement. For the convergence of the combined non-linearity. Newton-Raphson method is incrementally employed. Internally pressurized thick cylinder and eccentrically loaded column are chosen to test the effect of time increment on the solution.