Jo Jun 13, 2025
In the industrial field, production processes are becoming more complex and the requirements of the stability and reliability of operation and the quality of products are becoming stricter. Therefore, the study on fault diagnosis and estimation is of great significance and research on it is widely conducted.
There have been many studies on fault estimation using estimation of unknown input signals, and there are several such methods including augmented state estimation with unknown input. Such approaches are of practical significance because they can be effectively applied to fault diagnosis and fault tolerant control. Usually, fault estimation is carried out through three steps; fault detection, isolation and estimation. Only when the information on the size of fault is available, effective fault-tolerant control is possible
Jang Myong Jun, a researcher at the Faculty of Automation Engineering, has studied the robust fault estimation method for nonlinear discrete time systems by combining the general unknown input observation method and H∞ attenuation method, and proposed an observer algorithm guaranteeing the convergence of the observer and the required disturbance attenuation with respect to fault estimation error. In addition, he has solved fault estimation problems using linear matrix inequality (LMI), thus reducing calculation quantities.
The simulation results for a multi-tank system show that the proposed approach is effective.
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Jo Jun 12, 2025
Rapid development of IT has brought a change in the traditional attendance system. The Automatic Attendance System (AAS) identifies students to take attendance, and saves its result in the database to generate necessary information such as various statistics.
To identify students, it is necessary to read the information of physical means such as RFID (Radio Frequency Identification) card, or the biometric information such as their fingerprints or faces.
AAS based on RFID needs all students to carry their cards and involves manual operation when they forget to bring or lose it. In the meantime, the AAS based on fingerprints is fast and simple, and it needs no physical RFID cards. However, fingerprint readers must be installed at every lecture room and it takes long to recognize students by their fingerprints one by one.
Therefore, the AAS based on face recognition are accepted to be efficient as cameras are installed in most schools.
Recently, great progress in the field of face recognition has led to new applications of this technology, and the development of various products has been brisk. In a paper, they presented a system, called FaceNet, that directly learns a mapping from face images to a compact Euclidean space where face similarities are represented as distances. Once this space has been produced, tasks such as face recognition, verification and clustering can be easily implemented using standard techniques with FaceNet embeddings as feature vectors. This approach has great application effect as it shows great face recognition performance for face images of only 128 bytes.
The multi-face recognition system detects and recognizes several faces from an image, which requires high-resolution cameras. However, it is too expensive for some schools, and it is impossible to recognize all faces in a large classroom such as a practical training room because it usually has a view angle of 40 degrees. Of course, a high-resolution camera with a wide angle lens is a solution, but it is more practical to utilize the existing cameras than purchasing expensive new ones.
Kim Myong Jin, a lecturer at the Faculty of Information Science and Technology, has implemented multi-face recognition by combining several cameras and proposed an AAS based on it. This is a system that recognizes students’ faces from the images captured by existing different types of cameras, and automatically registers their attendance. For face recognition, FaceNet which shows high performance is used.
This system enables automatic register of attendance by means of low-resolution cameras even in large classrooms. The experiments have proved that the proposed system guarantees the accuracy of 100% in well-lit conditions with suitable allocation of cameras.
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Jo Jun 10, 2025
Electricity production is an important issue for our life. At present, power generation depends on fossil fuels. Excessive fossil fuel consumption by human activities has led to serious atmospheric and environmental problems including global warming, greenhouse gas emission, climate change, ozone layer depletion and acid rain. One of the energy generation methods to reduce the impact of natural disasters is thermoelectric conversion technology.
A thermoelectric generator produces electricity by using the thermoelectric effect. Thermoelectric generators consist of several sets of thermoelectric modules inserted between two heat exchangers. Each module is then composed of several tens to hundreds of pairs of thermoelectric couples connected together electrically in series and thermally in parallel, which directly convert some of the thermal energy that passes through them into electricity. However, the defects of thermoelectric technology are low energy-conversion efficiency and high material cost.
So far, different plans to get a higher degree of its efficiency have been suggested. Most of them, however, based on the main dimension of heat exchangers, focus on the influences of factors including temperature, velocity and flow direction in fluid, and the type of its internals, but not on the effect of the array of thermoelectric devices.
Kim Kwang Jin, a researcher at the Semiconductor Institute, has carried out a coupled fluid-solid numerical simulation of the heat exchanger internal flow field of a low-power thermoelectric generator using the waste heat from stove.
He carried out thermal field simulations in the heat exchanger with fins and without fins and an analysis of the shape of the inner fins, which were in good agreement with the results of the previous studies. Then, he determined the design parameters of the thermoelectric generator through the simulations according to the main dimensions, the number of inner fins and the arrangement of thermoelectric elements of the heat exchanger. He found that the performance of the heat exchanger is better, when the main dimensions of the heat exchanger is 250×200×30mm, the array of thermoelectric devices is linear and the internal topology of the heat exchanger is straight with 9 fins.
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Jo Jun 9, 2025
The environment of virtual motion chambers must be designed to be arbitrarily controlled according to the purpose. Main environmental parameters include temperature, humidity, CO2 concentration, and oxygen concentration. In order to measure and control these parameters, environmental sensors should be installed in various parts of the chamber for real-time monitoring control.
Existing sensors usually consist of a transducer that maps physical quantities to electrical signals, an analog-to-digital converter (ADC), a microprocessor, and an output interface that maps them to standard analog or digital signals. To measure physical quantities, the systematic error component can be modified by calibrating the sensors.
For noise filtering, hardware methods (e.g., installing analog active and analog passive reference frequency filters at the input of ADC or installing discrete active reference frequency filters at the output) or program filters (average filters, moving average filters, Kalman filters and artificial neural network filters) can be used. The device active reference filter is bulky and expensive, and consumes a large amount of power, and the passive reference frequency filter is less efficient, so it is most reasonable to use a program filter.
Under operating conditions, the input of the sensor has continuous signals, which vary randomly with time, and the rate of change is limited by physical reasons. In this case, a distorted signal appears at the output of the filter. The dynamic distortion of effective signals by the average filter and the moving average filter depends on the maximum rate of change of input signals. Therefore, it is effective to use the average filter or moving average filter when the change rate of input signals is not large.
Han Chol Hak, a researcher at the Faculty of Automation Engineering, has proposed an improved additive-mean algorithm that suits the characteristics of objects to improve the accuracy of oxygen concentration measurements in environmental sensors, and demonstrated the superiority of its filtering effect through comparisons with other algorithms.
The improved average algorithm can be used effectively for oxygen concentration sensing in embedded systems as well as for processing signals with low measurement signal variation and high noise intensity.
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Jo Jun 8, 2025
Graphene, a two-dimensional (2D) carbon nanomaterial, has attracted worldwide attention owing to its fascinating properties. Graphene, first manufactured by micromechanical exfoliation in 2004, has been regarded as a typical nanomaterial in the 21st century due to its great potential for use in various fields such as information industry, electronics, environment and energy, biotechnology, chemical industry, etc.
Graphene can be fabricated by electrochemical methods such as mechanical exfoliation of graphite, chemical vapor deposition (CVD) on copper film surface, cutting of carbon nanotubes, liquid phase exfoliation and Hummers method.
Since the unique properties of graphene are largely determined by its structure, it is important to study the number of layers that reflect its structural properties.
The methods for determining the number of layers of graphene include Raman spectroscopy, scanning electron microscopy (SEM), specific surface area measurement (BET), atomic force microscopy (AFM), and transmission electron microscopy (TEM). These methods have relatively high accuracy, but they require high cost and high-quality equipment.
Ri Ju Song, a researcher at the Institute of Nano Science and Technology, has proposed a method for determining the number of layers of graphene obtained by liquid phase exfoliation using XRD diffraction and Laue functions.
The results calculated by the Laue function model are in close agreement with the experimental data measured by Raman spectroscopy.
This method is relatively simple, but has the advantage of estimating the number of graphene layers with low cost and simple equipment.
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Jo Jun 6, 2025
Industries require conversion of alternating current of one voltage into another in many fields including electrical heating, lighting control and motor speed control.
Electronic transformers are direct AC-AC converters, which are used in various applications including cranes, turbines and elevator AC motors. Commonly used transformers are heavy with the core and windings, and they need large installation areas. In addition, they cause a large amount of loss due to iron loss even at no-load.
Electronic transformers operated by PWM control have the following advantages compared to conventional ones. First, their volume and weight are 50% and 30-40% of conventional ones of the same capacity, respectively. Second, conventional ones without control functions affect the other side when a short circuit or fault occurs on either input or output, but electronic transformers have a circuit-off function in the event of an accident. Third, by slowly increasing the output voltage at the time of turn-on, they can reduce inrush current or voltage shock into the load, and the addition of control functions can ensure power-off at no-load and compensation for non-sinusoidal input voltage.
Based on the principle of a boost DC/DC (direct current) converter, O Yong Hun, a researcher at the Robotics Institute, has described the advantages of a boost-type electronic transformer of light weight and small volume with protection function during the fault, and constructed the main circuit on a hardware basis so that it can operate like a conventional transformer, and then he has investigated the operation principle, control mode and energy conversion process when the devices are switched on and off.
In addition, he has constructed the main circuit and control system on MATLAB, and investigated the characteristics of the simulation waveforms at each tapping point. On the basis of the correlation between each factor, he has investigated the PWM (Pulse Width Modulation) control scheme for a reasonable parametric design to meet certain load conditions and for harmonic cancellation.
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