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.
The motion platform supports the trainee in experiencing a sense of reality in virtual space by performing a motion on the available degrees of freedom for a motion that mimics a specific motion in connection with a virtual reality content or a simulator. The required specification of the motor and driver of motion platform is determined by the target specification for the upward motion of the motion plate. The reason is that the weight of the upper plate always applies gravity in the direction of the downward motion. As a result, the downward motion has an excessive specification compared to the upward motion specification, resulting in an unbalanced motion specification. Additionally, a problem may occur in which a volume increases from the application of a high specification driving unit. In this paper, the motion platform was designed capable of three-axis motion in roll, pitch, and gravity directions using a compression spring to apply a load compensation mechanism. Based on the design results, the specifications of the compression spring for motion platform to satisfy the operating specifications do not excessively move the upward and downward direction derived by the analysis.
The purpose of this study was to investigate the springback behavior of magnesium alloy (AZ31B) at high temperature with respect to the holding time in the die-set. The changes of microstructure in the springback during V-Bending were analyzed. The springback of the magnesium alloy sheet showed a tendency to decrease as the forming temperature and the retention time in the die increase. In the microstructure analysis, there was minimal change in the microstructure at room temperature, while at high temperature the microstructure changed markedly. The increasing material holding time in die has been shown to reduce springback from internal energy reduction because of recrystallization and grain growth at high temperature.
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Analysis of acoustic emission signals during bending deformation of magnesium alloy sheet Jae-Hyeong Yu, In-Gyu Choi, Jung-Sik Yoon, John S. Kang, Wan-Jin Chung, Chang-Whan Lee Nondestructive Testing and Evaluation.2025; : 1. CrossRef
Analysis on the Warm Bending Process of Magnesium Alloy Sheet Using Additively Manufactured Polymer Die-Set Hyung-Won Youn, Jun-Hyun Kyeong, Keun Park, Chang-Whan Lee Journal of the Korean Society for Precision Engineering.2021; 38(10): 775. CrossRef
Study on the Time-Dependent Mechanical Behavior and Springback of Magnesium Alloy Sheet (AZ31B) in Warm Conditions Jae-Hyeong YU, Chang-Whan Lee Materials.2021; 14(14): 3856. CrossRef
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.
Recently the application of high strength steel sheets, such as DP, TRIP, and TWIP, is rapidly increasing in the automotive industry. Despite this trend, springback is still one of major obstacles that has yet to be overcome. In this study, we conducted U-draw bending experiments and analyzed the process with FEM, focusing on the springback. In the FE analysis, the effects of the hardening model ware studied by comparing the results among an isotropic hardening model, a combined isotropic-kinematic hardening model and the experiment. The effects of the restriking process on shape correction was also =studied by comparing the results of the springback analysis and the experiment.
As emission regulation of vehicles is being reinforced globally, the current requirement of the automobile industry are innovative green technologies that reduce the weight of the vehicle, thereby improving fuel consumption and the amount of exhaust gas emission. The application of ultra-high strength steel (UHSS) for vehicles has specifically been studied for light weight of vehicles. UHSS withstands greater loads than a general steel sheet of the same thickness. The spring-back and formability of the UHSS are also worse than general steel sheet due to their high elasticity and high yield strength. Various methods applied for processing UHSS include roll-forming and hot-press forming. However, these processes have not only high installation cost but also low productivity. This study therefore developed the cold-press forming method to overcome these disadvantages. The objective of this study is to determine the optimum conditions of the cold press required to form the upper seat track using UHSS. Forming analysis predicted the spring-back at each stage of the press forming. The prediction of spring-back was compared with the manufactured upper seat track by try-out, thereby reducing trial and error in the pressing process.
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Press Forming/Drawing Molding in the Radiator Support Mold Process of 440 MPa High Strength Steel Sheets Dong-Hwan Park, Tae-Gil Lee, Hyuk-Hong Kwon Journal of the Korean Society for Precision Engineering.2024; 41(1): 71. CrossRef
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Since the performance of the spring operating mechanism for a circuit breaker mainly depends on the dynamic behavior and mass of the coil spring, its dynamic analysis is required to evaluate the performance of the spring operating mechanism. In this study, a coil spring design program is developed for the spring operating mechanism. An experimental approach is used to find the variables satisfying the design constraints’ requirements. The coil spring is formed by using a lumped mass spring model. This program offers reference data for the design of coil springs and for the spring operating mechanism.
In sheet metal forming numerical analysis, the strain hardening equation has a significant effect on calculation results, especially in the field of spring-back. This study introduces the Kim-Tuan strain hardening model. This model represents sheet material behavior over the entire strain hardening range. The proposed model is compared to other well known strain hardening models using a series of uniaxial tensile tests. These tests are performed to determine the stress-strain relationship for Al6016-T4, DP980, and CP Ti sheets. In addition, the Kim-Tuan model is used to integrate the CP Ti sheet strain hardening equation in ABAQUS analysis to predict spring-back amount in a bending test. These tests highlight the improved accuracy of the proposed equation in the numerical field. Bending tests to evaluate prediction accuracy are also performed and compared with numerical analysis results.
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