Journal of the Korean Society for Precision Engineering

A Study on the Detection of Hole in Automotive CV Joint Boot Using Image Processing and AI Techniques: Yun-Hyeok Lim, Hyeongill Lee; J. Korean Soc. Precis. Eng. 2025;42(10):861-869.
Published online October 1, 2025; DOI: https://doi.org/10.7736/JKSPE.025.050

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Detecting and analyzing defects in components or systems is crucial for maintaining high-quality standards in modern manufacturing and quality control. Recently, imaging-based defect detection methods have gained popularity across various engineering fields, highlighting their growing importance. Additionally, the integration of Artificial Intelligence (AI) to improve accuracy and efficiency is rapidly advancing. This paper presents a system that uses imaging to detect holes in CV joint boots, as these holes significantly affect the overall performance and durability of the system. Moreover, it introduces a method for enhancing detection performance by applying AI techniques. Validation tests on actual CV joint boots confirmed that the proposed method improves detection performance.

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Development and Application of a Ball-on-plate Balancing System: Sangsin Park; J. Korean Soc. Precis. Eng. 2024;41(3):215-222.
Published online March 1, 2024; DOI: https://doi.org/10.7736/JKSPE.023.139

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The Ball-on-Plate Balancing System is a system where the base is fixed to the ground, and the plate is connected to the base through a spherical joint and can rotate in two directions (X-axis roll rotation, Y-axis pitch rotation). Two rotational joints are located on the orthogonal coordinate line of the base, and these joints are connected to the operational links of a 4-bar linkage, creating rotation of the plate around the spherical joint. The goal of this system is to prevent a ball placed on the plate from rolling off and maintain it at the center of the plate. A 17-inch touch panel attached to the plate allows the orthogonal coordinates of a ball placed on the plate to be measured. A cross-shaped frame was designed to secure the touch panel, and a custom universal joint was centered in this frame. The Ball-on-Plate Balancing System was integrated into a cart table, and a horizontal maintenance system was designed to keep the table level. Experiments confirmed the ability of the table to maintain its horizontal position during movements on uneven surfaces and sudden starts or stops.

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Design of a Controller to Overcome Air Ball in the Ball-on-plate System Applied to a Shelf Cart
Sangsin Park
Journal of the Korean Society for Precision Engineering.2025; 42(4): 301. CrossRef

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Structural Behavior Analysis of the Proximal Femur after Artificial Hip Joint Implantation at Micro Level: Seung Hun Ryu, Jung Jin Kim; J. Korean Soc. Precis. Eng. 2023;40(11):873-879.
Published online November 1, 2023; DOI: https://doi.org/10.7736/JKSPE.023.054

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Total hip replacement is a representative treatment for avascular necrosis of the femoral head. However, the stress shielding caused by the replacement induces dissociation of the artificial hip joint and various complications. Many studies have tried to explore the stress shielding but, most studies have been conducted at macro level and not at micro level. Thus, this study aimed to quantitatively analyze the structural behavior of the proximal femur according to total hip replacement at the micro level to explore the stress shielding. For this purpose, this study selected the artificial hip joint of the single wedge type and implanted the joint into a proximal femur that has a high resolution of 50 μm. Then the structural behavior of the implanted femur was analyzed by comparing that of the intact femur under three daily activity loads. As a result, the high possibility was confirmed that the stress shielding will occur in both cortical and cancellous bones under the one-legged stance movements. Additionally, it was discovered that the cancellous bone had a considerably lesser chance of adducting at an angle similar to the neck shaft angle of an artificial hip joint.

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Numerical Study on Ultimate Strength of Non-uniform Corroded Tubular T-joints under Compression: Vu Dan Chinh, Hà Thi Thu; J. Korean Soc. Precis. Eng. 2023;40(9):705-717.
Published online September 1, 2023; DOI: https://doi.org/10.7736/JKSPE.023.044

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The literature states that the existing guidelines mainly focus on the ultimate strength of uniform corroded joints in the Jacket-type re-assessment. However, joints are non-uniformly corroded in different shapes in reality. Results derived from theoretical equations in these scenarios are significantly different from the actual capacity of the frame joints. This paper studies the influences of thickness and corroded area on the T- joint’s ultimate strength for a chord based on the numerical model ABAQUS. Numerical results show the effects of location and dimension at corroded areas on the tubular joint ultimate strength. Moreover, this research proposes a new formula based on API to estimate the strength of T-joints connected with non-uniform corroded compressive braces in certain conditions. This equation is validated by comparison of the numerical simulation in independent cases.

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Wearable Inertial Sensors-based Joint Kinetics Estimation of Lower Extremity Using a Recurrent Neural Network: Ji Seok Choi, Chang June Lee, Jung Keun Lee; J. Korean Soc. Precis. Eng. 2023;40(8):655-663.
Published online August 1, 2023; DOI: https://doi.org/10.7736/JKSPE.023.042

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Recently, the estimation of joint kinetics such as joint force and moment using wearable inertial sensors has received great attention in biomechanics. Generally, the joint force and moment are calculated though inverse dynamics using segment kinematic data, ground reaction force, and moment. However, this approach has problems such as estimation error of kinematic data and soft tissue artifacts, which can lead to inaccuracy of joint forces and moments in inverse dynamics. This study aimed to apply a recurrent neural network (RNN) instead of inverse dynamics to joint force and moment estimation. The proposed RNN could receive signals from inertial sensors and force plate as input vector and output lower extremity joints forces and moments. As the proposed method does not depend on inverse dynamics, it is independent of the inaccuracy problem of the conventional method. Experimental results showed that the estimation performance of hip joint moment of the proposed RNN was improved by 66.4% compared to that of the inverse dynamics-based method.

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A Recurrent Neural Network for 3D Joint Angle Estimation based on Six-axis IMUs but without a Magnetometer: Chang June Lee, Woo Jae Kim, Jung Keun Lee; J. Korean Soc. Precis. Eng. 2023;40(4):301-308.
Published online April 1, 2023; DOI: https://doi.org/10.7736/JKSPE.022.112

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Inertial measurement unit (IMU)-based 3D joint angle estimation have a wide range of important applications, among them, in gait analysis and exoskeleton robot control. Conventionally, the joint angle was determined via the estimation of 3D orientation of each body segment using 9-axis IMUs including 3-axis magnetometers. However, a magnetometer is limited by magnetic disturbance in the vicinity of the sensor, which highly affects the accuracy of the joint angle. Accordingly, this study aims to estimate the joint angle using the 6-axis IMU signals composed of a 3-axis accelerometer and a 3-axis gyroscope without a magnetometer. This paper proposes a recurrent neural network (RNN) model, which indirectly utilizes the joint kinematic constraint and thus estimates joint angles based on 6-axis IMUs without using a magnetometer signal. The performance of the proposed model was validated for a mechanical joint and human elbow joint, under magnetically disturbed environments. Experimental results showed that the proposed RNN approach outperformed the conventional approach based on a Kalman filter (KF), i.e., RNN 3.48° vs. KF 10.01° for the mechanical joint and RNN 7.39° vs. KF 21.27° for the elbow joint.

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Development of Gait Measurement System Combined with IMU and Loadcell Insole: A Pilot Study: Jeong-Woo Seo, Junggil Kim, Seulgi Lee, Gyerae Tack, Jin-Seung Choi; J. Korean Soc. Precis. Eng. 2022;39(9):657-662.
Published online September 1, 2022; DOI: https://doi.org/10.7736/JKSPE.022.073

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In this study, an insole-type ground reaction force (GRF) measurement system using a load cell was manufactured and configured as a system that can measure joint angle and GRF, when walking in conjunction with a commercialized inertial sensor. The data acquisition device was used to acquire synchronized data, between the inertial measurement unit (IMU) sensor and the load cell insole. A three-dimensional motion analysis system comprising six infrared cameras and two ground reaction forces, was used to check the accuracy of the gait measurement system, comprising an inertial sensor and a load cell insole. The motion and force data were acquired while performing five times six-meter walking test by five young adult male subjects (Age: 26.0±1.8, Height: 171.4±6.8 cm, Weight: 62.2±10.8 kg). It was measured and as a result of comparing the calculated sagittal joint angle with the vertical GRF, the sagittal lower extremity joint angle correlation coefficient (Pearson’s r) was 0.40 to 0.94, and the vertical GRF to be 0.98 to 0.99. It is necessary to upgrade the joint angle calculation algorithm through future research. Additionally, the possibility of clinical application for actual stroke patients will be reviewed.

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A Study on the Improvement of Bonding Strength of Heterojunctions by Applying Laser Surface Treatment to Carbon Fiber Reinforced Plastics: Huan Wang, Seong Cheol Woo, Chung-Ki Sim, Seong-Kyun Cheong, Joohan Kim; J. Korean Soc. Precis. Eng. 2022;39(9):683-689.
Published online September 1, 2022; DOI: https://doi.org/10.7736/JKSPE.022.063

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The adhesive bonding technology of carbon fiber reinforced plastics (CFRP) and aluminum alloys, is one of the lightweight joining technologies for automobiles. The strength and properties of the bonded joint, depend on the surface of the bonded part that the adhesive touches. Thus, proper surface treatment is one of the most important steps in the bonding process. The laser surface treatment of carbon fiber composites is a new form of green and environmental surface treatment technology, which can effectively clean coatings and pollutants on the surface of materials. It is also possible to improve the bonding shear strength, by changing the microstructure and roughness of the material surface through laser micro texture processing, to form a mechanically interlocked structure. In this study, a pulsed laser was used to treat the surface of CFRP. By changing the scanning line spacing during laser micro texturing, the effect of laser micro texturing on the surface morphology of CFRP and the strength of aluminum alloy bonded joints was investigated. Results show that in the laser micro texturing process, when the scanning line spacing was 0.3 mm, the maximum tensile shear strength was 14.5 MPa, approximately 200% higher than that without laser treatment.

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Application of Artificial Neural Network for Compensation of Soft Tissue Artifacts in Inertial Sensor-Based Relative Position Estimation: Ji Seok Choi, Jung Keun Lee; J. Korean Soc. Precis. Eng. 2022;39(3):233-241.
Published online March 1, 2022; DOI: https://doi.org/10.7736/JKSPE.022.008

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Relative position estimation between body segments is one essential process for inertial sensor-based human motion analysis. Conventionally, the relative position was calculated through a constant segment to joint (S2J) vector and the orientation of the segment, assuming that the segment was rigid. However, the S2J vector is deformed by soft tissue artifact (STA) of the segment. In a previous study, in order to handle the above problem, Lee and Lee proposed the relative position estimation method using time-varying S2J vectors based on inertial sensor signals. Here, time-varying S2J vectors were determined through the joint flexion angle using regression. However, it was not appropriate to consider only the flexion angle as a deformation-related variable. In addition, regression has limitations in considering complex joint motion. This paper proposed artificial neural network models to compensate for the STA by considering all three-axis motion of the joint. A verification test was conducted for lower body segments. Experimental results showed that the proposed method was superior to the previous method. For pelvis-to-foot relative position estimation, averaged root mean squared error of the previous method was 17.38 mm, while that of the proposed method was 12.71 mm.

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Wearable Inertial Sensors-based Joint Kinetics Estimation of Lower Extremity Using a Recurrent Neural Network
Ji Seok Choi, Chang June Lee, Jung Keun Lee
Journal of the Korean Society for Precision Engineering.2023; 40(8): 655. CrossRef

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A Kalman Filter for Inverse Dynamics of IMU-Based Real-Time Joint Torque Estimation: Ji Seok Choi, Chang June Lee, Jung Keun Lee; J. Korean Soc. Precis. Eng. 2022;39(1):69-77.
Published online January 1, 2022; DOI: https://doi.org/10.7736/JKSPE.021.085

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One of the problems in inverse dynamics calculation for the inertial measurement unit (IMU)-based joint force and torque estimation is the amplified signal noises of segment kinematic data mainly due to the differentiation procedure and segmental soft tissue artifacts. In order to deal with this problem, appropriate filtering methods are often recommended for signal enhancement. Conventionally, a low-pass filter (LPF) is widely used for the kinematic data. However, the zero-phase LPF requires post-processing, while the real-time LPF causes an unignorable time lag. For this reason, it is inappropriate to use the LPF for real-time joint torque estimation. This paper proposes a Kalman filter (KF) for inverse dynamics of IMUbased joint torque estimation in real time without any time lag, while utilizing the smoothing capability of the KF. Experimental results showed that the proposed KF outperformed a real-time LPF in the estimation accuracy of hip joint force and torque during jogging on the spot by 100 and 29%, respectively. Although the proposed KF requires the process of adjusting covariance according to the dynamic conditions, it can be expected to improve the estimation performance in the field where joint force and torque need to be estimated in real time.

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Wearable Inertial Sensors-based Joint Kinetics Estimation of Lower Extremity Using a Recurrent Neural Network
Ji Seok Choi, Chang June Lee, Jung Keun Lee
Journal of the Korean Society for Precision Engineering.2023; 40(8): 655. CrossRef

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Additive Manufacturing of a Release Agent Injection Manifold for Hot Forging: Hak-Sung Lee, Min-Kyo Jung, Eun-ah Kim, Soonho Won, Do Wock Chun, Taeho Ha; J. Korean Soc. Precis. Eng. 2021;38(9):675-682.
Published online September 1, 2021; DOI: https://doi.org/10.7736/JKSPE.021.065

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In this study, design for additive manufacturing (DfAM) of release agent injection manifold for hot forging has been performed to achieve weight reduction and flow path optimization. The weight reduction of 53.5% was achieved, thereby enabling the application of stainless steel 316L, which has high strength and corrosion resistance. Lightweight manifolds using Al-Mg-10Si and SUS316L materials were fabricated by PBF-type metal 3D printer. The feasibility test showed that mold life was improved by 14% by solving residual release agent problem. In addition, the flow path optimization results suggested that the flow standard deviation of each outlet dropped sharply from 264 to 75 ㎤/s. This approach demonstrated that DfAM for release agent manifold could be applied to increase mold life and improve product quality and productivity for hot forging.

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Optimize Design of Flow Divider and Verification of the PBF 3D Printing Process
Jae-Hwi Lee, Jae-Ho Shim, Dong-Hun Sin, Yong-Seok Yang, Dong Soo Kim
Journal of Flexible and Printed Electronics.2024; 3(2): 249. CrossRef
Additive Manufacturing for Rapid and Precise Pattern Formation in Shoes Mold
Seok-Rok Lee, Eun-Ah Kim, Ye-Rim Kim, Dalgyun Kim, Sunjoo Kim, Soonho Won, Hak-Sung Lee
Journal of the Korean Society for Precision Engineering.2023; 40(3): 211. CrossRef

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Design of 4-Axis Scara-Type Robot for Attaching and Detaching Workpieces of Machine Tools: Seong-Gyu Yang, Gab-Soon Kim; J. Korean Soc. Precis. Eng. 2021;38(5):351-358.
Published online May 1, 2021; DOI: https://doi.org/10.7736/JKSPE.021.007

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This paper describes the design of a 4-axis SCARA-Type robot in the form of a scalar robot for the loading and unloading of workpieces in machine tools. The 4-axis dedicated robot is a 4-degrees-of-freedom robot consisting of a joint 1, 2, 3 motor and a 180° rotating gripper made up of a horizontal gripper and a vertical gripper. It was designed in a scalar shape that is suitable for machine tools, and the size of each link and elbow was determined through structural analysis. Through additional structural analysis, the deflection of the end center of the workpiece fixed to the horizontal gripper and the vertical gripper was designed to be within 0.1 mm, and based on the design result, a 4-axis SCARA-Type robot was manufactured, and the basic motion characteristics of the manufactured robot were tested. As a result of the characteristic test, the manufactured 4-axis SCARA-Type robot operated smoothly, so it is judged to be adequate for usage in loading and unloading the workpieces in machine tools.

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Design and develop a robot arm to automatically feed workpieces for laser engraving machines
Trung Xuan, Duy Anh
FME Transactions.2024; 52(4): 671. CrossRef
5-Axis Robot Design for Loading and Unloading Workpieces
Han-Sol Kim, Gab-Soon Kim
International Journal of Precision Engineering and Manufacturing.2023; 24(12): 2279. CrossRef

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Comparison of Ankle Joint Impulse while Descending Stairs and Ramp: Hyeong Min Jeon, Ju Hwan Shin, Jun Young Lee, Gwang Moon Eom; J. Korean Soc. Precis. Eng. 2021;38(3):209-214.
Published online March 1, 2021; DOI: https://doi.org/10.7736/JKSPE.020.103

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The purpose of this study was to compare ankle joint loads (Linear and Angular Impulses) while descending the stairs and ramp. Ten young male subjects participated in this study. Stairs and ramp of identical slope (30 degrees) were custom-made to include force plates in the middle of pathways. Subjects descended the stairs and ramp at a comfortable speed and posture. The stance period was divided into three phases, weight acceptance (WA), single limb stance, and pre-swing. Three-directional impulses and their sum were derived from the reaction forces and moments at the ankle joint. Differences in impulse sums (Both Linear and Angular) between stairs and ramp were significant only in the early (WA) phase, whereas those of stairs were greater than the ramp. All subjects adopted forefoot strike strategy for the stairs and 80% of the subjects adopted rearfoot strike strategy for the ramp. An increase in the GRF and moment arm of the GRF at the ankle joint in case of forefoot strike may have contributed to the increase in the linear and angular impulse in the early phase of stair descent compared to ramp descent. The results are in agreement with the preference of ramp in the elderly.

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Design and Analysis of Variable Stiffness Joint for Railway Vehicles Using Magneto-Rheological Elastomer: Yujeong Shin, Dahoon Ahn; J. Korean Soc. Precis. Eng. 2021;38(2):131-137.
Published online February 1, 2021; DOI: https://doi.org/10.7736/JKSPE.020.069

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The magnetorheological material changes its characteristics according to the external magnetic field. Magnetorheological elastomer existing in the solid phase has micrometer-sized magnetically responsive particles inside. When a magnetic field is applied by a permanent magnet or electromagnet nearby, it can exhibit stiffness that changes according to the strength of the magnetic field. Many previous studies focused on verifying the variability of the material"s characteristics. However, this study newly proposed a variable stiffness joint for the suspension system of railway vehicles using a magnetorheological elastomer, as a basic study of magnetorheological elastomer for a mechanical component. Based on the characteristics test of the magnetorheological elastomer, the variable joint was designed to have the same structure as the conventional guide arm joint of a railway vehicle. Particularly, to overcome the low magnetic field strength, which may be a problem in the previous research, and to implement uniform magnetic field distribution, the electromagnet was designed to make direct contact with the magnetorheological elastomer. A mathematical model was established and a finite element method verified the model, resulting in an average magnetic flux density of 300 mT, which means 30% stiffness change at 15% shear strain.

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Investigation of wheel-rail wear reduction by using MRF rubber joints with bidirectional adjustable stiffness
Ning Gong, Jian Yang, Weihua Li, Shuaishuai Sun
Smart Materials and Devices.2025;[Epub] CrossRef

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Design of Integrated Ankle Torque Sensor and Mechanism for Wearable Walking Aid Robot: Han-Sol Kim, Gab-Soon Kim; J. Korean Soc. Precis. Eng. 2020;37(9):667-673.
Published online September 1, 2020; DOI: https://doi.org/10.7736/JKSPE.020.037

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In this paper, an integrated ankle torque sensor and mechanism (Foot Link) of a Tendon driven-type wearing walking aid robot were designed. The foot link consists of an ankle torque sensor and a mechanism connected to the footrest. The size of the sensing part of the ankle torque sensor was designed through structural analysis and assembled by attaching a strain gauge. As a result, the reproducibility error and the nonlinearity error were within 0.04%, respectively. And the calibration result of the ankle torque sensor, reproducibility error, and non-linearity error were identified to be within 1%, respectively. Therefore, it is proposed that the ankle torque sensor presented in this paper can be used to measure the torque acting on the tendon-driven walking aid robot.

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