Electro discharge machining (EDM) is one of the most frequently used processing methods for machining conductive materials. Taguchi method combined with Grey relational method has been used to accommodate requests for multiple object functions in the EDM process. In the present study, an attempt was made to determine optimum parameters for minimum size of hole and number of shots. The size of the hole is related to the quality of the hole while the number of shots affects machining time. Grey relational analysis was used to determine optimal machining parameters. Electrode length and unit discharge were found to be the most significant parameters. Optimal conditions were: pulley position of 39 ㎜, voltage of 120 V, a capacitance of 1500 pF, and a resistance of 500 Ω. In experiments, such electrical conditions (voltage, capacitance, and resistance) generated electrical energy of 10 μj. Under these conditions, a micro hole of 184.9 ㎛ in average diameter could be machined with 16 shots.
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Analysis of Correlation between FDM Additive and Finishing Process Conditions in FDM Additive-Finishing Integrated Process for the Improved Surface Quality of FDM Prints Ji Won Yu, Hyung Jin Jeong, Jae Hyung Park, Dong Hun Lee Journal of the Korean Society for Precision Engineering.2022; 39(2): 159. CrossRef
In this study we investigated Kalman filter-based attitude estimation algorithms, considering external acceleration and bias effects in several different scenarios. Towards these goals, gyro biases were first estimated, or calibrated, in all three applied algorithms. Whereas external acceleration effects were not considered in the first algorithm, external acceleration effects were compensated for in the second and third algorithms, using the Kalman filter’s residual and acceleration model. Low, intermediate, and high external acceleration scenarios were then implemented in our test-bed. Three different rotational frequencies (0.3, 3, and 6 ㎐) for roll and pitch rotations were applied. Performance of each estimation algorithm was analyzed using slopes, y-intercepts, and standard deviations obtained from the linear regression. Our results confirm that attitude estimation errors are linearly proportional to the magnitude of the applied external acceleration. Perhaps most importantly, our results show the second algorithm may be used to provide relatively uniform and accurate estimation performance for low- and high-frequency motions.
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Inertial Sensor-Based Relative Position Estimation between Upper Body Segments Considering Non-Rigidity of Human Bodies Chang June Lee, Jung Keun Lee Journal of the Korean Society for Precision Engineering.2021; 38(3): 215. CrossRef
Drift Reduction in IMU-based Joint Angle Estimation for Dynamic Motion-Involved Sports Applications Jung Keun Lee, Chang June Lee Journal of the Korean Society for Precision Engineering.2020; 37(7): 539. CrossRef
In this paper, we designed and fabricated a hip joint torque sensor that can measure the torque applied to the hip joint of a walking assistant robot that can be used by a leg patient. To do this, we modeled the structure of the hip joint torque sensor so that it can be connected to the thigh link and the body of the walking assist robot. We calculated the rated torque of the hip joint torque sensor using computer simulation and determined the size of the torque sensor using a finite element program. The hip joint torque sensor was made by constructing a Wheatstone bridge and attaching a strain gauge. The characteristic test of the fabricated torque sensor was performed using a calibration device, and the reproducibility error and the nonlinearity error of the torque sensor were both less than 0.04%. Therefore, it is proposed that the developed hip joint torque sensor can be attached to the thigh link of the wearable walking assist robot, and the torque sensor can accurately measure the torque applied to the hip joint.
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Development of Lower Limb Rehabilitation Robot Capable of Adjusting the Size of Leg and Waist, and Analysis of Gait Trajectory Deviation Young-Ho Jeon, Gab-Soon Kim Journal of the Korean Society for Precision Engineering.2021; 38(11): 817. CrossRef
Gerotor oil pumps are widely used for the lubrication oil of an engine and the hydraulic source of an automatic transmission. Recently, improvements for the purposes of fuel efficiency and noise reduction have come to the forefront of the automobile industry, and it has become necessary to study the design of gerotors and ports. In this study, an expanded cardioid curve was developed, and an equation for a tooth profile with an expanded cardioid lobe shape has been suggested to reduce pump noise. The design was created using an automatic program; the program generated inner and outer rotor profiles and calculated performance parameters. Also, in order to decrease irregularity, CFD analyses were performed according to groove shapes in the exhaust port. Results showed the noise of the improved oil pump (the suggested gerotor [expanded cardioid] + the proposed port) was 5.44% lower than the existing oil pump (the existing gerotor [2-ellipse] + basic port).
Due to urbanization, parameters such as large size and height constrain the workspace of aerial lift truck. An aerial lift truck with reduced height was developed to decrease the telescopic boom. Based on FEM Analysis, the failure was localized to the shaft of the boom joint. Shape optimization was performed using the Design of Experiment based on three design factors. As a result, the maximum equivalent stress of boom joint was reduced by about 32.33%.
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Optimal Design of 50 ton Hydraulic Breaker Housing Jai Hak Lee, Dong Ju Lee, Jun Young Choi Journal of the Korean Society for Precision Engineering.2022; 39(4): 269. CrossRef
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Optimal Design of Boom for Telescopic Boom Type Forklift Truck Jai Hak Lee, Kang Su Kim Journal of the Korean Society for Precision Engineering.2020; 37(6): 457. CrossRef
Nowadays, noise, vibration, and harshness (NVH) is a comprehensive issue related to manufacturing quality, it gives the purchaser the most direct and superficial feeling. Following economic development, the improvement of people’s living standards, and the expansion of the export market, it has become urgent to develop and produce some better NVH performance motorcycles. In this paper, the transmission of a scooter gearbox is modeled and analyzed by software. Then, the first helical gear pair of the gearbox was investigated through static analysis. Lastly, optimized modification was verified using B&K testing equipment in the semi-anechoic room. The comparison of the simulation to prototype during testing showed a good correlation, which means simulation optimization can greatly improve the research and development efficiency of the transmission system.
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Study on the Reduction of Gear Whine Noise in Diesel Engine Gear Train Qi Zhang, Yong Bo Wang, Jian Hua Lv, Zhong Gang Zhu, Zhen Qin, Sung Ki Lyu Journal of the Korean Society for Precision Engineering.2019; 36(9): 867. CrossRef
The worsening environmental pollution has increased the interest in developing eco-friendly technologies. The purpose of this study is to develop an aero-heat exchanger to reduce the emission of environmental pollutants. The operating conditions of an aircraft are extremely harsh, leading to challenges with the determination of appropriate materials and structures that can withstand the severe conditions. In addition, since the tubes brazed to the tube-sheet are structurally fragile, it is essential to assess the structural integrity of tubes. In this study, the overall structural integrity of the tubular heat exchanger under development was evaluated. An appraisal of the junctions between tubes and tube-sheet, which are the most critical parts, was conducted. A finite element (FE) analysis was employed for the assessment of structural integrity. FE analysis was used to evaluate the brazed joint of tubes using a model in which specific tubes were designed to withstand the high temperature of the tube-sheet. The evaluation was carried out compared with the fatigue strength of Inconel 625, the material constituting the heat exchanger.
In this paper, the reliability-based parameter study is carried out for the stamping process of a front rail roof member with the ultra high strength steel, considering the scatters of the material properties and the process parameters. With the reliability-based design optimization (RBDO) scheme, the springback tendency is investigated from the perturbation of the process parameters such as the sheet thickness, ultimate tensile strength, yield strength, Coulomb friction coefficient, and applied padding force. The amount of the elastic recovery along the height direction is quantified to describe the springback tendency from the analysis. The analysis shows the springback-amount scattering is not ignorable when the yield stress scatters within the similar range of the ultimate tensile strength. The analysis results fully explain the importance of controlling the scatters as well as the average yield-strength amount in the mass production of the stamped products.
Various techniques for separating mixed oil and water have been developed for the purpose of controlling marine oil pollution and for the purification of wastewater containing oil from industrial processes. In this work, we fabricate porous polydimethylsiloxane (PDMS) capsules to develop a high-performance, selective oil absorber. A template method using a sugar cube is used to fabricate the porous PDMS structure by dissolving the sugar template after infiltrating it with the PDMS solution. A hollow capsule structure was prepared by controlling the infiltration time of the PDMS into the sugar template. Contact angle measurements revealed the highly porous surface of the PDMS capsule maximized the differences between hydrophobicity and oleophilicity, which improved the absorption selectivity of oil from water. The fabricated PDMS capsules exhibited superhydrophobic and superoleophilic wetting properties; the oil droplets were absorbed into the PDMS capsule upon contact, while the water droplets were not absorbed with a contact angle above 170˚. Since the absorbed oil can be stored in the capsule pores, the oil absorption capability per unit weight of the absorber is highly increased. The adsorption performance and recyclability of the PDMS capsules were also evaluated using various waste oils.
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Variations in the Compressive Modulus of Porous PDMS with Mixing Conditions Chae Won Lee, Tae Woon Yoon, Sanghyun Lee, Jongkyeong Lim, Sangmin Lee Journal of the Korean Society of Manufacturing Process Engineers.2024; 23(4): 54. CrossRef
In this study, the mechanical and frictional properties of Polydimethylsiloxane (PDMS) were investigated. PDMS has received much attention because of its numerous advantages such as good formability, high transparency, light weight and low cost. However, PDMS has relatively poor mechanical properties compared to other materials, and it is vulnerable to surface damage or wear due to contact. As a result, there is a need to investigate the mechanical properties and enhance its tribological characteristics. In this study, PDMS specimens with different stiffnesses were prepared. The mechanical properties of PDMS were measured using a rigid spherical indenter. Sliding tests were performed to evaluate the frictional properties of the PDMS specimens under both dry and lubricated conditions. The effect of stiffness on the frictional properties of PDMS was assessed, In addition, sliding tests under various lubricated conditions were performed and the effect of the viscosity of the lubricant was also investigated. It was found that the mechanical and frictional properties of PDMS depended upon the stiffness of PDMS and the lubrication condition.
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Synergistic effect of sharkskin-inspired morphologies and surface chemistry on regulating stick-slip friction Liguo Qin, Xiaodong Huang, Zongsheng Sun, Zeyu Ma, Fagla Jules Mawignon, Baohua Lv, Lei Shan, Guangneng Dong Tribology International.2023; 187: 108765. CrossRef
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Friction and Wear Characteristics of Polydimethylsiloxane under Water-Based Lubrication Conditions Sung-Jun Lee, Yoon-Chul Sohn, Chang-Lae Kim Materials.2022; 15(9): 3262. CrossRef
Friction and wear reduction effect of glass bubbles embedded in PDMS surface Sung-Jun Lee, Gang-Min Kim, Chang-Lae Kim Journal of Mechanical Science and Technology.2022; 36(4): 1997. CrossRef
Effect of Glass Bubbles on Friction and Wear Characteristics of PDMS-Based Composites Sung-Jun Lee, Gang-Min Kim, Chang-Lae Kim Coatings.2021; 11(5): 603. CrossRef
Hemispherical Microelectrode Array for Ex Vivo Retinal Neural Recording Yoonhee Ha, Hyun-Ji Yoo, Soowon Shin, Sang Jun Micromachines.2020; 11(5): 538. CrossRef
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Conventional prosthetic hands require users to activate designated muscles or press buttons to select among predefined grasping patterns. These methods are time-consuming and increase muscle fatigue. This study proposes a regression model that differentiates multiple muscle activation patterns allowing the user to select a desired grasping pattern. We classified four hand primitives and three force intensities, which can reflect the intention of prosthetic hand users. An 8-channel band-type sEMG sensor was used to measure myoelectric signals from an amputated upper-arm. To acquire the sEMG data, the amputee was instructed to imagine four hand primitives (fist, open hand, flexion, and extension) with three levels of force intensity (low, medium, and high). Time-domain features (mean average value, variance, waveform length, and root mean square) were extracted from the sEMG signal and classified using a Support Vector Machine. The hand primitives and force intensities had accuracies of 95% and 90%, respectively. Results indicate the regression model reflected the user’s intention to select different grasping patterns, and is thus expected to improve the quality of life of amputees.
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Continuous grip force estimation from surface electromyography using generalized regression neural network He Mao, Peng Fang, Yue Zheng, Lan Tian, Xiangxin Li, Pu Wang, Liang Peng, Guanglin Li Technology and Health Care.2023; 31(2): 675. CrossRef
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This paper proposes an air pocket glove for finger rehabilitation and diagnosis of hemiplegic patients after stroke. This device consists of pneumatic actuators that expand when air is injected from a pump motor, silicone flexors that act as artificial finger tendons, film-type bending sensors, and a pressure sensor. As air enters the glove, the actuators are expanded, thus stretching out paralyzed fingers. We designed two different rehabilitation modes: continuous passive motion (CPM) mode and master-slave mode, where the motions of the unaffected fingers are duplicated in the affected fingers. We conducted an experiment to test the validity of the device for each mode. In CPM mode, the patient’s spasticity level was estimated from finger angle and air pressure. Our results showed that spasticity level decreased 13% from the initial level after rehabilitation. With the master-slave mode, EMG signals were additionally measured and compared to those found during conventional therapy, which revealed a positive effect stemming from voluntary involvement in the exercise. As a result, EMG energy was shown to increase up to 18% during master-slave mode.
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Analysis of maintaining human maximal voluntary contraction control strategies through the power grip task in isometric contraction Jinyeol Yoo, Woong Choi, Jaehyo Kim Scientific Reports.2024;[Epub] CrossRef
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A Wearable Soft Robot for Stroke Patients’ Finger Occupational Therapy and Quantitative Measures on the Joint Paralysis Jihun Kim, Geonhui Lee, Hanjin Jo, Wookhyun Park, Yu Shin Jin, Ho Dong Kim, Jaehyo Kim International Journal of Precision Engineering and Manufacturing.2020; 21(12): 2419. CrossRef
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