Jo Mar 14, 2025
The permanent magnet synchronous motor (PMSM) is widely used in the robotics and motion control systems due to its compact structure, low noise and high torque to inertia ratio. PMSM is a typical multivariable and nonlinear system with strong coupling and uncertain model parameters. Therefore, traditional linear control methods such as PID control cannot guarantee high control performance for PMSM systems.
Though many advanced nonlinear control methods including adaptive control, nonlinear optimal control, fuzzy logic control and neural network control have been used for PMSM systems, they have their own advantages and shortcomings.
Ri Tae Hyong, a researcher at the Robotics Institute, has proposed a full order terminal sliding mode (FOTSM) controller to solve the speed tracking problem for a PMSM system by combining RBF neural network and FOTSM control scheme.
First, in order to eliminate chattering in conventional sliding mode control (SMC), he developed a continuous FOTSM technique. Then, he designed a FOTSM speed controller based on RBF neural network, in consideration of the presence of external disturbance.
The simulations and PMSM speed control experiments by MATLAB have proved that the proposed method is effective.
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Jo Mar 13, 2025
High-intensity focused ultrasound (HIFU) has been investigated as a noninvasive surgical method for the treatment of tumors located in various tissues including brain, prostate, liver, kidney and breast. When the ultrasonic beams emitted from the transducer is focused into the target tissue, the temperature in the focal region rises above 56℃ in a short time, which results in tissue necrosis without damaging overlying or surrounding tissues.
Recent efforts in HIFU research have been focused on the treatment of uterine fibroids. Uterine fibroid is benign neoplasm that occurs in approximately three out of four menopausal women. The incidence rate of this disease in pregnant women is 25%-30%. Several treatment methods currently exist for uterine fibroids but they have some serious shortages. For instance, hormone therapy is a noninvasive method to treat fibroids but if medication is discontinued, fibroids regrow. These show that HIFU therapy is better than others.
Since the most important requirement in the HIFU therapy is safety, the consequences of the therapy must be predicted before treatments of tumors. Thus, a proper model for predicting the temperature distribution by ultrasound source in a human body is needed.
Kim Sang Jin, a researcher at the Faculty of Physical Engineering, has described and simulated geometrical and mathematical models of the thermal coagulation necrosis region caused by HIFU radiation on the human uterus for different types of transducers and frequencies.
He used two models for the HIFU simulation. In one model, only the linear parts in the Westervelt equation was considered, and in the other one, thermal conduction and viscosity were included. He compared the differences in the temperature distribution for both models, varying the shape of transducer and the frequency.
The results show the shape of transducer and the frequency greatly affect the temperature field in the uterine fibroid.
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Jo Mar 12, 2025
At present, fabrication of micro-scale components and devices is one of the major technologies with considerable potential, and it is of great importance to make manufacturing processes suitable for their medium and large-scale production.
In the last decade, there has been an increasing demand for micro-sized components and their microstructures, which has led to the introduction of micro-injection molding technology to fluid control techniques and medical tools. The most promising process of this technology is micro powder injection molding (μPIM), a product manufacturing technology for producing small size components of complex shapes in large quantities.
However, the μPIM process suffers from several difficulties, unlike the PIM process. In the μPIM process, there is a high demand for powder. For example, the fluidity of raw material depends on the type and size distribution of powder, and the size change after debinding depends on the friction force between particles. In addition, the lubricity of the binder depends on the particle surface conditions, and the debinding rate also depends on the particle morphology, particle size, etc. Raw material powder should be less than 5㎛ in size. The composition of the binder used for mixing raw materials has a great influence on the product's molding and demolding. That is, it needs to have high viscosity. The temperature should be well controlled at the time of debinding of various mixed binders to eliminate cracking during sintering of products and to ensure dimensional accuracy after sintering.
Ri Un Sim, a researcher at the Faculty of Materials Science and Technology, while preparing a 800㎛ micro-gear from 1Cr18Ni9 stainless steel spray powder using μPIM technique, has analyzed the effects of injection temperature, injection pressure and injection speed on the formation of components.
As a result, she has found that injection molding is best at the injection temperature of 130℃, scanning pressure of 70㎫ and scanning rate of 60mm/s.
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Jo Mar 11, 2025
In recent years, it has become a pressing issue in practice to modernize the fish quick-freezing process and increase its productivity in keeping with the huge increase in the catch. The main objective of increasing the amount of quick-freezing production is to automate, streamline and control the quick-freezing process on a high level, along with the use of high-performance quick-freezing equipment. For this purpose, it is necessary to determine appropriate design parameters of a lifting up-down machine (LUDM) for quick-freezing.
So far, there have been many studies on LUDM. At present, machines for transshipping mushroom substrate cases are in use in mushroom farms and LUDMs are used for tiles and roofing tiles in the building materials industry. LUDM for fish quick-freezing has two guide pillars, which involves tipping risk during operation.
Pak Myong Nam, a researcher at the Robotics Institute, has modeled LUDM for fish quick-freezing on SolidWorks, carried out a stability analysis by ADAMS, and determined the design parameters by the quality engineering technique.
Thus, he ensured high accuracy and automation of LUDM, which improved the quality and hygienic safety of fish quick-freezing, saved a lot of labor and realized the automation of the overall fish quick-freezing process.
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Jo Mar 9, 2025
In enhancing the role of the logistics enterprises, evaluation of the ability of enterprises in a scientific and effective way is of great importance. Accurate assessment of the ability of logistics enterprises can help to find the right way to ensure their development.
There are several methods for logistics performance measurement including AHP (analytic hierarchy process), multivariate statistical analysis (principal component analysis, factor analysis, etc.), etc., which have their own advantages and disadvantages for their application.
Fuzzy comprehensive evaluation is a comprehensive evaluation method that applies fuzzy mathematical methods when fuzziness is involved in the process of comprehensive evaluation of objects, and thus it is regarded as a practical analytical method for evaluating the capabilities of logistics enterprises.
Song Kwang Hyok, a section head at the Faculty of Management of Industrial Economy, has set the weight of indexes like management level, technical strength, transport capacity, informatization level, competitive power and customer service capacity by AHP, and proposed a method of evaluating the capacity of logistics enterprises by fuzzy comprehensive evaluation using M (1, 2, 3).
The proposed approach allows enterprises to understand their own capabilities and to take necessary measures to improve their business performance.
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Jo Mar 7, 2025
Recently, there have been many studies on the wide use of MOS-FET pH sensors modified with functionalized carbon nanotubes. However, no comprehensive and detailed study on the OH and N functionalization and pH sensing properties of multi-walled carbon nanotubes (MWCNT) has been found in the literature.
Pak Il Man, a section head at the General Assay Office, has studied the OH and N functionalization of MWCNTs and investigated their pH-sensing properties by modifying functionalized carbon nanotubes onto MOS-FETs.
First, he boiled MWCNTs in 63% HNO3 (analytically pure) at 120℃ for 40h, and filtered and washed them with deionized water to perform OH functionalization. Then, he carried out treatments by boiling them in 20% liquid ammonia and 0.1% gelatin solution, respectively, and by applying ultrasonic dispersion to the samples boiled in gelatin solution and conducting ultrasonic dispersion in 0.1% gelatin solution, respectively, to investigate the N functionalization properties.
He investigated the pH characteristics by modifying the MOS-FET drain with functionalized carbon nanotubes, and found that the pH-sensitive linear range of MOS-FET modified with N-functionalized carbon nanotubes was longer than that of MOS-FET modified with OH-functionalized carbon nanotubes.
As the pH sensor based on this is a strike and temperature resistant integral solid, it is possible to measure pH accurately in a coarse suspension that is stirred in a closed container or in a high temperature solution.
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