In an environment where ultra-high-precision equipment is used, vibration inevitably occurs due to various factors. These vibrations generate fatal effects, such as defect generation and reduced production yield, on ultra-high-precision production equipment. Among the multiple methods for solving vibration problems, a Tuned Mass Damper (TMD) is a useful technique that reduces vibration without changing the existing structure by attaching a passive dynamic system consisting of additional mass, spring, and damper. However, it is difficult to realize fine-tuning of the system parameters for optimal performance because the passive elements have structural limitations. An active TMD, which has a form wherein sensors, actuators, and a control device are added to the passive TMD structure, was introduced. It has higher performance than passive TMD because dynamic characteristics can be induced to stable and highly damped by a well-designed control algorithm realized by software in the control device. In this study, an active TMD was developed utilizing passive TMD with a voice coil actuator and attached to the center of both end fixed beam that assumed a single-degree-of-freedom structure. A dual-loop control algorithm using a non-minimum phase system was designed for a high-damped response while retaining stability. The modal test was performed for experimental evaluation and excellent performance of active TMD was verified.
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Investigation on Vibration Reduction of Automotive Seat Using Dynamic Dampers Based Design of Experiment Soul Kim, Jaehyeon Nam, Dongshin Ko Transaction of the Korean Society of Automotive Engineers.2023; 31(12): 1045. CrossRef
This paper deals with the development of a passive modular hip exoskeleton system aimed at preventing musculoskeletal low back pain, which commonly occurs in heavy weight transport workers, by improving back muscle strength. The passive exoskeleton system has the advantage of being lightweight, making it suitable for modular exoskeleton systems. The cam and spring actuator designed in this study was applied to the passive modular exoskeleton system to build human hip and lumbar muscle strength. In order to evaluate the effectiveness of the passive modular exoskeleton system, a test was performed in which a subject lifted a 15 kg weight three times in a stoop posture, using heart rate measurement and Borg scale recording. According to the results, all subjects showed 26.83% lower maximum heart rate and 34.73% lower average heart rate than those who did not wear the system, and Borg scale evaluation result was lower. All subjects wore this system and did not experience back pain during the experiment. Through this study, we validated the effectiveness of the passive modular exoskeleton system and proved that this system can build the strength of industrial workers and be a solution to prevent musculoskeletal lumbar disease.
Power electronic systems have been widely applied in both industrial and domestic applications in the modern society for controlling and converting electrical energy. Due to their characteristics, such as excellent performance, low cost, high reliability, and low weight and size, power semiconductors, including insulated-gate bipolar transistors (IGBTs) dominate the market of power converters. The technical progress and development trend of IGBT for industrial applications are primarily driven by five aspects influenced by each other to an extent, including operating temperature, efficiency, dimension, reliability, and cost. Liquid cooling systems surpass the air cooling systems by supplying heat transfer coefficient, which is several orders of magnitude higher. Thus, using liquid cooling system enables much higher power densities of power modules and more compact converter solutions.
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Experimental Study on Heat Transfer Performance of Microchannel Applied with Manifold Jungmyung Kim, Hoyong Jang, Heesung Park Journal of the Korean Society for Precision Engineering.2022; 39(12): 923. CrossRef
As interest in the quality of life has recently increased, there is a growing interest and demand for exercise equipment, such as indoor treadmills or cycles, which can be used at home. However, the use of such indoor exercise equipment has caused social problems by generating noise between floors and causing inconvenience to neighbors. In particular, treadmills that generate a lot of vibration during use cause more social problems in an assembly building, such as an apartment. The purpose of this study is to design dampers of various shapes and to develop dampers with high vibration damping effects through vibration analysis. The damper was installed at the lower end of the treadmill to reduce vibration from the product. Three types of dampers were designed by referring to the damper shape of the existing treadmill, and the vibration reduction effect of each damper shape was verified through structural analysis of the magnitude of vibration generated from the bottom surface of each damper.
Additive manufacturing (AM) had a significant influence on the geometry design of products. It became possible to replace the full solid material with cellular structures for the optimal design of AM parts. Various types of cellular structures have been developed and studied for different purposes. However, many studies have focused on an optimal design using cellular structures having near-isotropic properties, such as cube or honeycomb structures. This paper presents the effect of the anisotropic material property on the optimal design by generating cellular structure with anisotropic material property induced by internal void geometry. Kriging metamodel-based material property model is proposed for modeling anisotropy induced by the rotation of internal void. This material model is then applied to the optimal design process. Three types of void geometry, circular, non-rotating, and rotating elliptical void, are considered to demonstrate the effect of anisotropic cellular structure on the optimal design. Due to the anisotropy induced by complex internal void geometry, Kriging metamodel-based material property models are utilized as the material property model. The effect of the anisotropic property and the material property model on the optimized structures is confirmed through two numerical examples in the perspectives of structure performance and density distribution.
ISO 10791-6 specifies test conditions, BK1 and BK2, including circularly interpolated motions by simultaneous control of two linear axes and a rotary/tilting axis, for five-axis machine tools with a tilting-rotary table. Eccentricities of measured motions are used to identify position-independent geometric errors of the rotary/tilting axis. However, time-consuming alignments of measurement devices are required to execute the circular motions due to large geometric errors of the tilting axis. In this paper, a simple method is proposed to align an initial position of a tool-center-point (TCP) relative to the actual tilting axis of five-axis machine tools for application of ISO 10791-6. A ball at the tool nose with an extension fixture, supplied commercially by a double ball-bar manufacturer, is used to measure positional deviations of a ball on workpiece table at 90° command angle of a tilting axis. An alignment error of a TCP is identified simply by using a geometric relationship of the TCP and measured deviations. Then, identified alignment errors are used to calculate initial position of a TCP for fine measurements of position-independent geometric errors specified in ISO 10791-6. The proposed method is applied to a five-axis machine tool and verified experimentally.
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A Study on the Estimation of Geometric Errors for Rotary Axes of a Five-Axis Machine Tool Using a Cross-Shaped Calibration Artifact Jeongmo Kang, Dayoung Kim, Sungchul Jee Journal of the Korean Society for Precision Engineering.2023; 40(1): 87. CrossRef
A TCP Calibration of a 6-Axis Manipulator and Geometric Errors Identification of a Tilting-Rotary Table Kwang-Il Lee, Do-Hun Kim, Hoon-Hee Lee, Seung-Han Yang Journal of the Korean Society for Precision Engineering.2022; 39(4): 253. CrossRef
An electrospray is widely used in the industry due to uniform and continuous droplet generation. Most of the studies on the electrospray modes are conducted in the cone jet mode. The goal of this study is to confirm the spray patterns for each mode of the electrospray by setting various conditions, such as nozzle to substrate, nozzle diameters, fluid properties (Viscosity and Conductivity), and flow rate. As a result, 7 modes were observed by the applied voltage and flow rate. It was confirmed that the smallest droplet size was produced in the cone jet mode and working fluid V (High Conductivity).
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Experimental Investigation of Electrospraying Properties Based on Ring Electrode Modification Ji Yeop Kim, Sang Ji Lee, Mun Hee Lee, Jung Goo Hong ACS Omega.2024; 9(1): 1125. CrossRef
Study on Correlation between Manufacturing Method of Thermal Insulation Fabric and Thermal Insulation Performance for Reducing Rail Temperature in Summer Season Juyeop Park, Donghoon Kang Journal of the Korean Society for Precision Engineering.2024; 41(4): 313. CrossRef
Study of Droplet Characteristics of Electrospray Coating Method as a Function of Ring Electrode Parameters Ji Yeop Kim, Mun Hee Lee, Jun Yeop Kim, Jung Goo Hong Journal of the Korean Society for Precision Engineering.2024; 41(2): 153. CrossRef
Periodicity of Droplet Impact Behavior by Liquid Viscosity on PDMS Surface Dong Kwan Kang, Sangmin Lee Journal of the Korean Society for Precision Engineering.2022; 39(11): 857. CrossRef
Spray Mode and Monodisperse Droplet Properties of an Electrospray Ji Yeop Kim, Sang Ji Lee, Jung Goo Hong ACS Omega.2022; 7(32): 28667. CrossRef
Viscosity Effect on the Electrospray Characteristics of Droplet Size and Distribution Ji Yeop Kim, Sang Ji Lee, Gwang Yeol Baik, Jung Goo Hong ACS Omega.2021; 6(44): 29724. CrossRef
Farming is a typical task that includes repetitive tasks, incomplete working positions, and weight work, along with exposure to a number of musculoskeletal diseases and harmful factors. Therefore, in this study, work clothes were developed for older agricultural workers exposed to musculoskeletal diseases and alienated from the medical system. Work clothes can help in repetitive cropping and support the load on the work, preventing and mitigating farmers" diseases. To verify the effectiveness of the developed clothing, six men in their 20s were evaluated for muscle usage before and after wearing the clothing in two ways: stoop lifting and squat lifting. The results of this study showed that the mass of most muscles, except the gastrocnemius muscle, was reduced during lifting operations by stoop lifting after wearing work clothes. The reason why the gastrocnemius was more activated was that the ankle joint was greatly activated by dorsal flexion. For squatting and lifting, most of the muscle usage was reduced. In future research, we want to analyze the muscle characteristics of actual agricultural workers on wearing work clothes.
As global warming is rapidly emerging as one of the inherently global issues, one of the renewable energies, i.e. thermo-electric generation, has received attention. In order to increase the efficiency of thermo-electric generation, a maximum temperature difference in plain fins in a heat exchanger is needed, and an appropriate pressure drop is required to ensure stable flow of high temperature fluid. In the present study, the characteristics of the temperature difference and pressure difference for the 2 kW-class thermo-electric generator installed in exhaust pipes of a cogeneration plant were investigated numerically via thermal fluid analysis using ANSYS CFX. Then, size optimization for plain fins of a heat exchanger was carried out using SAS JMP, in which the temperature difference was maximized while meeting the requirement of a given pressure drop condition. A meta-model was generated by using the response surface model, and individual desirability functions were defined to derive the optimal solution that provided the maximal overall desirability function. The result obtained by size optimization showed that the temperature difference of the optimized plain fins of a heat exchanger increased by approximately 27% in comparison with the original model under the given pressure drop condition.
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