Jo Mar 20, 2023
Obstacles in self-mixing (SM) based displacement sensing are time-consuming estimation of parameters such as an optical feedback factor and a linewidth enhancement factor, and the complex algorithm of displacement retrieval.
There have been presented fringe counting (FM) method and consecutive samples based unwrapping (CSU) method to avoid such complexities.
However, the FC method has very low resolution and the CSU method requires normalization of SM signals (SMSs), which is very complicated and even impossible when SMSs are affected by a speckle noise.
Kim Chol Hyon, a researcher at the Faculty of Physical Engineering, has proposed a new method of displacement reconstruction with high resolution, which does not need any complex processes such as parameter estimation or normalization. In addition, the method can be applied to all feedback regimes and work well even when SMSs are subject to a speckle noise.
He has presented a direct simple method of reconstructing the displacement of the target from self-mixing signals based on the velocity of the target for a weak feedback regime. Also, he has reported a simple method of displacement retrieval for moderate and strong regimes.
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Jo Mar 19, 2023
A research team led by Kim Myong Il, a section head at the Faculty of Mechanical Science and Technology, has designed a CNC hobbing machine for dry and wet cutting by high-speed tools or carbide cutting tools, in consideration of future development in the field of cutting tools.
This machine consists of a machine body, a control panel, a control cabinet, a cooling and chip removal device, an oil pump, etc. It is designed for handsome appearance, in conformity with human-machine engineering demand, and for convinience of machining, maintenance and material conveying.
With 6 control axes and 4 simultanous axes, it can cut spur gears, bevel gears, worm wheels and non-circular gears such as elliptic gears.
The technical characteristics of the machine are as follows.
Maximum work piece diameter: 500mm
Modulus range of gear machining: 1.5~6
This machine has remarkably upgraded machining accuracy and productivity and is good for environmental protection.
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Jo Mar 17, 2023
Measurement of low concentration oxygen gas is very important in chemical processes where several kinds of material gas and fuel gas are used. If the concentration of combustible oxygen gas gets high, it might cause explosion, which will have vicious influence upon the whole process. So, real-time measurement of oxygen at low concentration is essential for taking proper measures.
Two common techniques for sensing oxygen at low concentration are luminescent optical sensing and electrochemical sensing. Both demonstrate high sensitivity to low concentration oxygen. Fluorescent oxygen sensing has seen widespread adoption thanks to its inherent stability. However, application of this technique is limited due to complicated fabrication and short life time. On the other hand, electrochemical sensors are widely used and available in different forms according to the demands of users.
A research team led by Choe Chol Man, an institute head at the Faculty of Electronics, made an amperometric oxygen sensor based on the electrochemical method to manufacture an oxygen concentration measuring instrument, and introduced a refrigerator and a gas cleaning instrument for removing the effect of interference elements, thus completing a system of measuring low concentration oxygen gas.
The left picture shows the construction of the oxygen sensor incorporating a cathode, an anode, an electrolyte solution and a gas permeable membrane, all of which affect the characteristics of the sensor. They used silver with good oxygen reduction characteristics as a cathode, and silver/silver chloride electrode as an anode. KCl saturation solution and PTFE thin film were selected as an electrolyte and a gas permeable membrane, respectively.
They introduced digital signal processing technology to remove atmospheric noises so that the instrument could work properly in any operation environment, thus ensuring the stability and reliability of the instrument. The right picture shows the installation of the system.
The specification of the system is as follows.
Measurable band: 0~10%
Response time: 30s
Accuracy: 0.1%
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Jo Mar 14, 2023
A research team led by Kim Thae Ung, a section head at the Faculty of Automation Engineering, has established an integrated automation system of the ore dressing process for the production of apatite concentrate.
The system supports comprehensive monitoring and operation of a whole process by displaying process data including the information of operation state of motors in crushing processes, grinding processes and flotation processes, pulp density, flotation temperature, pH value, amount of reagent consumption and level of industrial water numerically and graphically. It saves data of process variables of the subprocesses in the corresponding data base.
The process interface consists of process monitoring, grinding process, flotation process, reagent supplier, operation mode and process history.
The system shows several advantages. The ore dressing recovery and the concentrate grade are guaranteed at over 80% and 30% respectively. The reagent consumption is reduced by more than 10% and the labor is economized by 15%.
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Jo Mar 10, 2023
Jang Rim Chol, a researcher at the Faculty of Mechanical Science and Technology, has developed a CNC engraving machine for cutting an EPS model.
The machine ensures high geometric accuracy and surface finish in cutting EPS models for lost form casting.
It consists of a computer, a control device, a mechanical system, an exhaust fan, etc.
What is new about it is the development of a spindle unit for EPS cutting and a rolling guide using ball bearings. Also, it has a rotary table that can change its rotating axis vertically and horizontally, so the machine offers satisfactory cutting of the EPS model of a spur gear whose diameter is 2 meters. The machine is also applicable to complex and large EPS models such as large bevel gears, housings and manikins.
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Jo Feb 28, 2023
Fast constructions from the Brownian motion and Brownian bridge are required in many applications such as Quasi-Monte Carlo simulations and statistical inferences on stochastic processes. A simple method for construction of discrete Brownian motion is a step-by-step method of computing the cumulative sum of i.i.d. normal variables.
The construction of N dimensional discrete Brownian motion (or a N-1 dimensional discrete Brownian bridge) that requires at most O(NlogN) floating point operations (flops) is called fast construction. Discrete Brownian motion can also be constructed using decompositions of its covariance matrix, and the method based on eigenvalue decomposition not only shows superior performances in many simulations over the step-by-step method but also becomes a fast construction. Usually the discrete Brownian bridge can be constructed from the discrete Brownian motion using the linear relationship between them. The inserting method using a decomposition of covariance matrix of discrete Brownian bridge gives another decomposition of covariance matrix for high dimensional discrete Brownian motion and it is very significant in Quasi-Monte Carlo simulations for financial derivatives.
Ri Sung Hyon, a section head at the Faculty of Applied Mathematics, has obtained eigenvalue decomposition of covariance matrix for discrete Brownian bridge and LDU (Lower-Diagonal-Upper) decompositions for covariance matrices of discrete Brownian motion and bridge newly and then proposed new fast construction methods on the basis of them. He has also proposed an inserting method for construction of discrete Brownian motion using eigenvalue decompositions which requires O(Nlog(logN)) flops.
The proposed new construction methods might be used effectively in simulations using Brownian motion and Brownian bridge. In addition, the construction algorithms would be used in analytical study for Brownian motion and Brownian bridge.
You can find more information about this in his paper “Decompositions of the Covariance Matrix of the Discrete Brownian Bridge: New Fast Constructions of Discrete Brownian Motions and Brownian Bridges” published in “American Journal of Applied Mathematics”.
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