Jo Mar 28, 2023
A research team led by Cha Pong Il, a section head at the Faculty of Mechanical Science and Technology, has developed a multi-rotor UAV that could enjoy wide use in agriculture.
The agricultural multi-rotor UAV is a piece of battery-powered up-to-date mechanical equipment for scattering various agricultural chemicals and fertilizers, and taking and transmitting the photographs of crops.
Iron-shell construction is used for its safe operation under 15-kilogram effective load.
Its specification is as follows.
Flight velocity: 5-10m/s
Flight altitude: 3-10m
Endurance: 15-20 minute
Effective mass : 15㎏
Take-off mass: 40㎏
Working area (1 time): 1 hectare
Temperature condition: -10~40℃
The effectiveness of the agricultural multi-rotor UAV is as follows.
Scattering of agricultural chemicals, fertilizer and seeds by a multi-rotor UAV enhances working efficiency remarkably, about 100 times higher than by human. It will do all kinds of harmful work like agricultural chemical spray, which leads to the improvement of working conditions for farmers. It consumes no fuel, so it is environmentally-friendly.
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Jo Mar 26, 2023
Although it appears that enough researches have been made as regards the estimation of the optical feedback factor C of a self-mixing interferometer, no method of the C estimation can ensure its reliability if the operation of the self-mixing displacement sensor covers the strong feedback regime with fringe loss due to large displacement of a target.
That is the main reason why the precision of the sensor degenerates for measurement of large displacement.
Kim Chol Hyon, a researcher at the Faculty of Physical Engineering, has proposed a novel C estimation method called region tracking for C value, which is indispensable for measurement of long-range displacement, and demonstrated its fidelity experimentally.
He classified the fringe loss which arises in moderate and strong feedback regimes into an individual fringe loss and a collective fringe loss. Then, he clarified that the individual fringe loss is induced due to the hysteresis of the self-mixing effect and the collective fringe loss due to the minimum line width mode competition principle.
The displacement reconstruction based on the proposed region tracking method ensures better precision than a half wavelength, depending on the method of displacement retrieval. The approach presented will make a great contribution to further improvement of the accuracy of the self-mixing displacement sensor for large displacement.
For more information about this, please refer to his paper “Improvement of precision of self-mixing displacement sensor based on region tracking for large displacement” published in “Optics Communications” (SCI).
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Jo Mar 25, 2023
Sodium hypochlorite antiseptic solution (NaOCl) has been widely used all over the world to prevent the spread of epidemic diseases. However, due to its low sterilizing power, it needs high concentration of activated chlorine, which is harmful to the human body and environment and results in the corrosion of metal products.
Scientists found that disinfection is caused by hypochloric acid(HOCl), not sodium hypochlorite (NaOCl) and recommended using hypochloric acid with pH 6~7.2, ORP≧900mV for disinfection. Accordingly, hypochloric acid is being produced by electrolysing admixed solution of NaCl, HCl and H2O in electrolytic baths without diaphragms, but this method is restricted in its output.
A research team led by Choe Hyon Ho, a section head at the Faculty of Electronics, has succeeded in preparing neutral electrolytic water with hypochloric acid by mixing sodium hypochlorite (NaOCl), chlorhydric acid (HCl) and water (H2O) sodium hypochlorite antiseptic solution at the sodium hypochlorite antiseptic solution production sites existing in the DPRK.
They determined the ratio of additional amount of chlorhydric acid to the mixing amount of water for preparing neutral electrolytic water through some basic experiments.
The preparation method can satisfy the demand for neutral electrolytic water with hypochloric acid for several uses with less consumption of salt, electrolytic plates and electric power than before.
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Jo Mar 23, 2023
When silicon is anisotropically etched, the etch rate of individual crystal planes of silicon is different from one another. Therefore, corner undercutting in KOH solution is critical and it is difficult to form full convex corners without compensation. Consequently, an abnormal square structure can be generated, which affects the operation characteristics of elements.
In the fabrication of diaphragms for a pressure sensing unit with square-shaped convex corners, compensation patterns should be arranged in each corner so that the beam part, where resistances are set up, is not changed by etching.
Several compensation methods have been used to solve this problem. Triangular, square and banded compensation patterns have been widely used to protect rectangular edges and these are now recognized to be classic compensation methods.
However, general principles to design individual compensation structures and compensation patterns, especially formulae to determine the dimension of compensation patterns do not seem to be introduced in detail.
Jon Chung Hyok, a researcher at the Faculty of Semiconductor Institute, has proposed a method to determine the shape and dimension of reasonable compensation patterns to make very thin diaphragms from 10~15㎛ to 250~300㎛ in thickness with square mass.
First, for fabrication of V-grooves structures with mass by corner compensation, he showed the compensation mechanism by several compensation patterns. The experiments on different types of compensation patterns showed that a diagonal-type compensation pattern is the best in performance. However, when etching depth should be ranged from 150㎛ to 200㎛, this compensation pattern is not suitable for compensation because the dimension of the mass and diaphragm should be restricted along their edges.
Next, on the analysis of the experimental results, he determined conditions for V-grooves structure from the given compensation pattern.
He concluded that when two types of compensation patterns are combined, the dimension of a square compensation pattern should be calculated before compensated corners with band compensation patterns are used to satisfy the insufficient etching depth, in order to increase the compensation effect.
Subsequently, he has made a diaphragm with the mass where a/h is less than 3.72 and b/h is less than 3.33 by applying corner compensation patterns.
More information about this is found in his paper “V-grooves Structures of Semiconductor Pressure Sensors with mass by Convex Corner Compensation” published in “Journal of Analog and Digital Devices” (EI).
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Jo Mar 22, 2023
Choe Myong Guk, a section head at the Faculty of Mechanical Science and Technology, has developed a system to find errors in mechanical drawings designed on SolidWorks software.
The system helps to promptly detect and correct errors in the dimension, surface finish symbols and geometrical tolerance in drawings.
The system consists of 3 modules: structurized module, analyzing module and post-processing module.
The structurized module serves as a preprocessing module which imports necessary data from SolidWorks models and converts it into a more convenient form for analyzing errors. It can be seen as a communication module because it manages data transfer between SolidWorks software and the check system.
The analyzing module is the most important kernel in the system because it detects errors from structured data. AI technology is introduced to the module to find dimensional errors such as over-dimension, lack-dimension and wrong dimension in drawings. It can also find errors in surface finish and geometrical tolerance symbols that do not satisfy technological and economic conditions. It can find 90% of errors that might occur in mechanical part drawings, assembly drawings and sheet metal drawings.
The post-processing module is a terminal module of the system. It highlights errors detected by the analyzing module in different colors and symbols. In addition, it exports checked drawing files to other file formats such as PDF.
The system will prove to be useful in the machine building industry or design examination institutes by detecting and correcting errors in mechanical drawings before production.
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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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