Jo Feb 17, 2026
A cascade control system is a multi-loop control system that can be implemented effectively for a controlled object that is capable of measuring any intermediate control variable directly affecting the primary control variable. In cascade control systems, the intermediate sensor and controller are used to effectively reject the disturbances before they affect the primary control variable.
In a cascade control system, the inner loop control system is usually designed as a fast response system, and the outer loop control system is designed as a little slower system than the inner loop system.
Due to the good disturbance rejection and fast convergence performance, many studies have been conducted to design a sliding mode control (SMC) for the inner loop controller of a cascade system. With the improvement of chattering effect, SMC controllers have been used for not only the inner loop system, but also the outer loop control system.
To the best of our knowledge, no efforts have been focused on the relationship between the outer loop sliding surface and the inner loop sliding surface of cascade control systems.
Kim Sok Min, a researcher at the Faculty of Automatics, designed the inner loop sliding surface as a hierarchical sliding surface containing the outer loop sliding surface, and proposed a hierarchical sliding mode controller so as to reduce the outer loop reaching phase and improve the entire convergence. Furthermore, in order to improve the steady-state performance, he designed an adaptive PID sliding surface to improve the reaching phase using the proportional-integral-differential (PID) sliding surface.
The numerical simulations verified the excellent performance of the proposed design method.
If more information is needed, you can refer to his paper “An improved fast convergent sliding mode control design of a cascade system based on the hierarchical structure and an adaptive PID sliding surface” in “Second International Conference on Electronics, Electrical, and Control System (EECS 2025)” (EI).
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Jo Feb 16, 2026
The linear control system for LTI (linear time invariance) plant has a limitation in control performance. So far, many approaches such as nonlinear control, intelligent control, fractional order, etc. to break this limitation have been proposed. Among them, the approach based on fractional order description provides great possibility to improve the control performance by greatly expanding the control area of the controller and the control targets.
It is expected that most design methods for linear control systems provide positive effects if they are extended to fractional order version.
Pak Se Yang, a section head at the Faculty of Automatics, who was motivated by such expectation, conducted a study to extend the robust controller design method in the frequency domain under study, into the fractional order controller.
The controller has the structure of linear combination of fractional basis transfer functions with respect to parameters. The problem for controller design is solved by finding the parameters which satisfy the approximated linear inequalities corresponding to H∞ norm condition for the robust criterions.
He investigated the problem to design the fractional PI and PID controllers through a simulation, which verified the validity of the proposed method.
You can find the details in his paper “Data-Driven Design of Fractional Order H∞ Controller by Convex Optimization” in “International Journal of Dynamics and Control” (EI).
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Jo Feb 15, 2026
Flow shop scheduling with blocking time is a problem with zero buffer and it has been widely studied in recent years. In particular, minimizing makespan is the most popular objective function in blocking flow shop scheduling problems. Hence, it is urgent to develop an effective algorithm for minimizing the makespan in the blocking flow shop.
So far, many researches have been conducted on blocking flow shop scheduling for minimizing makespan, but no literature presents a mathematical model considering the machine blocking time for this problem.
Rim Kum Chol, a researcher at the Faculty of Automatics, proposed a flow shop scheduling model aimed at makespan minimization considering the machine blocking, and an improved genetic algorithm based on some genetic operations tailored to the problem.
First, he presented a mathematical model of the blocking flow shop scheduling problem by introducing the new consideration of machine blocking. Second, he proposed an improved genetic algorithm using some tailored genetic operators such as the order crossover and the fragment inversion interchange mutation.
The proposed algorithm can be applied to not only blocking flow shop scheduling problems but also other scheduling problems and even to many optimization problems with some modifications.
For more information, please refer to his paper “Improved Genetic Algorithm for Flow Shop Scheduling Problem with Machine Blocking to Minimize Makespan” in “Second International Conference on Intelligent Transportation and Smart Cities (ICITSC 2025)” (EI).
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Jo Feb 13, 2026
A circular vibrating screen, a kind of reciprocating vibrating screens, has two advantages over other types of sifters: smaller production area compared to a large screen mesh, and higher separation efficiency due to the longer relative motion of material particles. The unique feature of a circular vibrating screen is its three-dimensional motion in the space, which leads to high screen efficiency, high throughput and low power consumption. In addition, due to its simple structure and easy assembly and disassembly, different raw materials can be sorted by grain size in a single plant.
The materials in the circular vibrating screen perform sliding and projection motions while drawing a spiral motion path on the screen surface during sieving. This motion is due to the use of a vertically installed vibrating motor vibrating device that provides the spatial motion of the screen box. Here, the sliding and projection motions of the material affect the path of the material on the screen surface and provide the material delivery rate that allows the material to move outward to the screen surface. Especially, when the materials are in a projection motion, the materials in the material layer are mixed with each other, and the opportunity for fine particles to pass through the screen increases the sieving efficiency. Therefore, the sliding and projection motions of raw materials should be controlled properly to ensure constant throughput and improve screening efficiency.
Many researchers have worked on determination of the parameters of a circular vibrating screen that are being applied to its design. It is very important to clarify the theory of the motion of material on the vibrating surface in determining the kinetic parameters of a vibrating machine, but unfortunately, the kinetic theory of material on the surface of a circular vibrating screen has not been studied in detail.
Hwang Je Hyon, a section head at the Faculty of Mechanical Science and Technology, conducted a dynamic analysis of a circular vibrating screen and the motion characteristics of screen surface, based on which he carried out a theoretical analysis of sliding and projection motions of material, and then, he verified it using EDEM.
The analysis results are as follows.
First, the screen surface of a circular vibrating screen undergoes a plane rotational motion around the vertical symmetry axis and a swinging motion around the center of mass.
Second, the theoretical transport rate of the material sliding motion in a straight vibrating screen is proportional to the angular frequency and vibration amplitude, whereas in a circular vibrating screen, it is proportional to the angular frequency and oscillation angle.
Third, the projection index of material motion at the end of the screen surface of a circular vibrating screen can be determined from 3 to 7 taking into account the motion characteristics of material and the strength of vibrating parts. In this case, the sieving properties tend to improve gradually and then deteriorate again.
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Jo Feb 12, 2026
The deep-cooling oxygen plant is now widely industrialized because of its highest production capacity and the highest purity of separated gas of all other oxygen plants. The deep-cooling oxygen plant is an air-liquefaction separator that uses compressed air to swell the throttle, obtain the cold, devolatilize the air, and then distill the devolatilized air at low temperature to obtain gases such as oxygen, nitrogen, argon, etc.
Expanders are widely used because they are energetically more advantageous to obtain cold than throttling expansion of compressed gas. At present, turbo-expanders are widely used in the production of oxygen by the deep-cooling method. In oxygen plants, a turbo-expander accounts for 80-90% of the total cold production.
High-strength aluminum alloys are used for the working wheels of a turbo-expander since they rotate at such cryogenic temperatures as -186℃ to -175℃ at high rotational speeds (18 300-18 600r/min). Recently, with the improvement of the mechanical properties of casting materials by the development of casting technology, many researches have been carried out to fabricate efficient closed working wheels by the casting method. What is important here is to choose proper material for working wheels.
Sok Sun Hak, a researcher at the Faculty of Material Science and Technology, proposed a new method for optimizing the alloy composition and heat treatment process parameters of turbo-expander working wheel materials by using quality index and quality engineering techniques, and obtained the optimum parameters.
The additive amount of RE is 0.1%, and the optimum heat treatment process is to perform solid solution treatment before aging heat treatment at 155℃ for 8h. The mechanical properties of this case were excellent, with yield strength of 287MPa, tensile strength of 380MPa and elongation of 12.7%.
This improvement in the mechanical properties ensured stable operation of working wheels in a large oxygen plant and made it possible to increase their lifecycle by three times as much as that of existing ones.
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Jo Feb 10, 2026
An ecological industrial park consists of several factories and enterprises. Here, there exist connection chains, where the products, semi-finished products and waste of any enterprise are used as the materials or energies for production of other enterprises.
The key to developing a successful ecological industrial park and setting up a balanced ecological relationship among relevant enterprises is to determine the connections between different enterprises in the ecological industrial park. Particularly, a material and energy flow relationship among different enterprises that established chains to form an inter-dynamic structure is needed. If such structure is impossible, an ecological industrial park cannot be formed.
Ri Jun Hyok, a researcher at the Institute of Mirae Industrial Technology, proposed an ecological chain index of an ecological industrial park by applying the general theories of ecology, and then drew the relations between the ecological chain indexes and the recycling rates of semi-finished products and wastes. In addition, he proposed a method for evaluating ecological industrial parks by using the ecological chain index.
First, he defined the ecological chain index of an ecological industrial park, and provided its calculation equation. Second, he defined semi-finished products and wastes of an ecological industrial park and provided its calculation equation. Then, he provided a relational expression of the recycling rate of semi-finished products and wastes and of its ecological chain index.
The ecological chain index and the recycling rate of semi-finished products and wastes can be applied to the planning and construction of ecological industrial parks.
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