Bae Ho Park

Fault diagnosis systems are used to improve the productivity and reduce the costs of the manufacturing process. However, the feature variables in existing systems are extracted based on the classification performance of the final model, thereby limiting their applications to models with different conditions. This paper proposes an algorithm to improve the characteristics of feature variables by considering the cutting conditions. Regardless of the frequency band, the noise of the measurement data was reduced through an oversampling method, setting a window length through a cutter sampling frequency, and improving its sensitivity to shock signal. An experiment was subsequently performed to confirm the performance of the model. Using normal and wear tools on AI7075 and SM45C, the diagnosis accuracies were 97.1% and 95.6%, respectively, with a reduction of 85% and 83%, respectively, in the time required to develop a diagnosis model. Therefore, the proposed algorithm reduced the model computation time and developed a model with high accuracy by enhancing the characteristics of the feature variable. The results of this study can contribute significantly to the establishment of a high-precision monitoring system for various processing processes.

Bearings have various uses in industrial equipment. The lifetime of bearings is often lesser than anticipated at the time of purchase, due to environmental wear, processing, and machining errors. Bearing conditions are important, since defects and damage can lead to significant issues in production processes. In this study, we developed a method to diagnose faults in the bearing conditions. The faults were determined using kurtosis, average, and standard deviation. An intrinsic mode function for the data from the selected axis was extracted using empirical mode decomposition. The intrinsic mode function was obtained based on the frequency, and the learning data of ANN (Artificial Neural Network) was concluded, following which the normal and fault conditions of the bearing were classified.

We have studied ferroelectricity in ultrathin (down to 5 nm) PbZrO₃/PbTiO₃ artificial superlattice by scanning probe microscopy (SPM). Synchrotron x-ray diffraction patterns showed only (00l) reflections. The average c-axis lattice parameters decreased with decreasing film thickness from 20 nm down to 5 nm along with the decrease in piezoresponse signal. By means of piezoresponse images and d₃₃ hysteresis measurement using piezoresponse force microscope (PFM), we demonstrated that the atomically smooth superlattices showed the uniform polarized domain patterns and ferroelectric polarization switching. The results reveal that the superlattice retains a stable ferroelectricity down to 5 nm thickness, although with a reduced piezoresponse signal.

(La,Sr)CoO₃/Pb(Zr,Ti)O₃/(La,Sr)CoO₃ (LSCO) heterostructures have been grown on LaAlO₃ substrates by pulsed laser deposition (PLD) to investigate asymmetric polarization switching of Pb(Zr,Ti)O₃ (PZT) thin films with different electrode configuration. P-V hysteresis loop of LSCO/PZT/LSCO was symmetric. However, LaCoO₃ (LCO)/PZT/LSCO showed a largely asymmetric P-V hysteresis loop and large relaxation of the remanent polarization at the negatively poled state, which means that the negatively poled state was unstable. On the other hand, LSCO/PZT/LCO exhibited large relaxation of the positively poled state. The asymmetric behavior of the polarized states implies the presence of an internal electric field inside the PZT layer. It is suggested that the internal electric field caused by built-in voltages at LCO/PZT and LSCO/PZT interfaces. The built-in voltages at LCO/PZT and LSCO/PZT interfaces were 0.6 eV and 2.1 eV, respectively.

Using La_0.5Sr_0.5CoO₃(LSCO) or Pt film as a bottom electrode layer, epitaxial Bi₄Ti₃O₁₂(BTO) thin films were deposited on MgO(001) substrates by pulsed laser deposition. X-ray diffraction patterns showed that the c-axes of BTO films are oriented normal to the substrate surface. Interestingly, an epitaxial Pt/BTO/Pt film showed a strongly preferred polarization state directed towards the top electrode in spite of the symmetric electrode configuration. The inprint state did not change significantly in the pulse test with DC bias. These anomalous behaviors suggest that the imprint characteristic is highly correlated with interfacial states between the electrodes and the BTO films. To understand space charge effects in the metal-ferroelectric contacts, imprint characteristics of the thin film capacitors with various top electrodes were investigated. Auger Electron Spectroscopy(AES) depth profile was measured, to check the possibility of a interdiffusion of the bottom electrode with the BTO layer. Interdiffusion (or reaction) between the BTO and Pt (bottom electrode) seems to be responsible for the strongly preferred polarization.