Journal of the Korean Society for Precision Engineering

Position Control of a Linear Motor Motion Stage Using Augmented Kalman Filter: Keun-Ho Kim, Hyeong-Joon Ahn; J. Korean Soc. Precis. Eng. 2025;42(11):887-892.
Published online November 1, 2025; DOI: https://doi.org/10.7736/JKSPE.025.011

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The rapid growth of semiconductor and display manufacturing highlights the demand for fast, precise motion stages. Advanced systems such as lithography and bio-stages require accuracy at the μm and nm levels, but linear motor stages face challenges from disturbances, model uncertainties, and measurement noise. Disturbances and uncertainties cause deviations from models, while noise limits control gains and performance. Disturbance Observers (DOBs) enhance performance by compensating for these effects using input–output data and a nominal inverse model. However, widening the disturbance estimation bandwidth increases noise sensitivity. Conversely, the Kalman Filter (KF) estimates system states from noisy measurements, reducing noise in position feedback, but it does not treat disturbances as states, limiting compensation. To address this, we propose an Augmented Kalman Filter (AKF)–based position control for linear motor stages. The system was modeled and identified through frequency response analysis, and DOB and AKF were implemented with a PIV servo filter. Experimental validation showed reduced following error, jitter, and control effort, demonstrating the improved control performance of the AKF approach over conventional methods.

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imulation Study on Line-of-sight Stabilization Controller Design for Portable Optical Systems: Jae Woo Jung, Sang Won Jung, Jae Hyun Kim, Seonbin Lim, Youngjin Park, Onemook Kim, Jaehyun Lim, Jae Ho Jin, No-Cheol Park, Jun Young Yoon; J. Korean Soc. Precis. Eng. 2025;42(2):175-183.
Published online February 1, 2025; DOI: https://doi.org/10.7736/JKSPE.024.126

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This paper presents a line-of-sight (LOS) stabilization control method for portable optical systems by analyzing fast steering mirror, image sensor, and gyro sensor system. To compensate for LOS errors caused by hand tremors in portable optical systems, we present the configuration of an image sensor-based LOS stabilization control system and a control strategy considering the phase delay effect caused by low sampling frequency of the image sensor. The phase delay effect of the image sensor caused restricted bandwidth, which limited the stabilization performance. To overcome such limitations, we present disturbance feedforward control using the gyro sensor and controller design method considering characteristics of the gyro sensor. Through overall system modeling, we constructed a control simulation model. The LOS stabilization performance against hand tremor disturbances was analyzed based on the proposed controller design. Simulation results demonstrated that integrating a gyro sensor-based disturbance feedforward control with the image sensor-based LOS stabilization control significantly enhanced the stabilization performance.

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A study of Tuned Mass Damper (TMD) Application for Mass Imbalance and Vibration Reduction in Gimbal Systems for High-speed Maneuverable Vehicles: Jun-Soo Kim, Dong-Kyun Lee, Jong-Kuk Lee, Hyeon-Jun Cho, Ji-in Jung; J. Korean Soc. Precis. Eng. 2024;41(11):857-864.
Published online November 1, 2024; DOI: https://doi.org/10.7736/JKSPE.024.079

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This study proposed a method for simultaneously reducing mass imbalance and vibration in gimbal systems utilizing a tuned mass damper (TMD) as a balancing weight. Finite element analysis (FEA) and experiments were used for testing the method. Mass imbalance in gimbal systems generally causes external disturbance torque. To reduce this, a balancing weight can be used. However, weight increase due to balancing weight causes resonance in the gimbal system, which generates bias error in the gyroscope sensor. This study demonstrated that both mass imbalance reduction and vibration reduction effects could be achieved by utilizing a TMD as a balancing weight. FEA results showed that the mass imbalance reduction effect of the gimbal was not affected by TMD. The magnitude of vibration response at the resonance point was reduced by about 98% with TMD. When a TMD was applied, the magnitude of the vibration response at the resonance point was reduced by 98% to the same level as that of the gimbal. Bias error of the gyroscope sensor was reduced by about 95% or more. These results show that a TMD is useful for effectively reducing mass imbalance and vibration in gimbal systems while improving gyroscope sensor performance.

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Control Boost of a Magnetic Levitation System with Disturbance Observers: Yupeng Zheng, Hyeong-Joon Ahn; J. Korean Soc. Precis. Eng. 2024;41(4):273-278.
Published online April 1, 2024; DOI: https://doi.org/10.7736/JKSPE.023.142

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A magnetic levitation system (MLS) controls the position of a steel ball with the magnetic force of the electromagnetic actuator. A disturbance observer (DOB) could improve the disturbance rejection and command tracking performance of the voltage-controlled MLS. This paper studied control boost of MLS using current and position DOB. The current-controlled MLS had a higher control performance than the voltage-controlled MLS. The combination of PID position and PI current controls provided stable levitation and a wide operation range of MLS. When DOB was applied to PI current control, it could compensate for inductance change according to the position of the steel ball. In addition, when another DOB was introduced to the PID position control, it improved the disturbance removal performance. Finally, we discussed the effectiveness and limitations of the DOB-based current and position control by measuring closed-loop frequency responses.

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Improvement of the Transient Levitation Response of a Magnetic Levitation System Using Hybrid Fuzzy and Artificial Neural Network Control
Yupeng Zheng, Hyeong-Joon Ahn
International Journal of Precision Engineering and Manufacturing.2025; 26(5): 1159. CrossRef

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Model-based Motion Control Design of a Linear Motor Stage in Frequency Domain: Hee Won Jeon, Hyeong-Joon Ahn; J. Korean Soc. Precis. Eng. 2024;41(1):55-60.
Published online January 1, 2024; DOI: https://doi.org/10.7736/JKSPE.023.107

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The fourth industrial revolution led to advanced servo systems, enhancing productivity across industries. However, designing these systems remains challenging due to the performance-stability trade-off. This paper presents a model-based motion control of a linear motor motion stage in frequency domain. A user-code for the PowerPMAC commercial controller was developed to excite motion control system so that we could get a frequency response. The theoretical frequency response of the servo algorithm was compared with the experimental frequency response. Based on this, a tuning graphical user interface (GUI) was developed to predict performance when the servo loop gain is changed. Especially, to compensate for residual vibrations caused by high acceleration and deceleration and to improve tracking error, DOB (Disturbance Observer) and ILC (Iterative Learning Control) control techniques were applied in the frequency domain. Through the design of the frequency domain motion controller, the control performance of the linear motor motion stage could be predicted with over 96% accuracy, resulting in a 54.32% improvement in tracking error and a 93.56% improvement in settling time, 85.29% in RMS error.

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Disturbance Rejection and Robust Tracking Using a Compound Control Approach for RFC Linear Motor Motion Stage
Kyung Ho Yang, Hyeong-Joon Ahn
International Journal of Precision Engineering and Manufacturing.2026;[Epub] CrossRef
Fuzzy Neural Network Control for a Reaction Force Compensation Linear Motor Motion Stage
Kyung Ho Yang, Hyeong-Joon Ahn
International Journal of Precision Engineering and Manufacturing-Smart Technology.2024; 2(2): 109. CrossRef
Customized Current Control of a Linear Motor Motion Stage
Kyung Ho Yang, Hyeong-Joon Ahn
Journal of the Korean Society for Precision Engineering.2024; 41(11): 875. CrossRef

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Frequency Domain Identification and Model-based Disturbance Observer for a Mini Drone: Kyu-Hwan Chung, Hyeong-Joon Ahn; J. Korean Soc. Precis. Eng. 2023;40(5):383-388.
Published online May 1, 2023; DOI: https://doi.org/10.7736/JKSPE.022.134

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Drone is an innovative industry that can combine the application of various technologies in the fourth industrial era, such as big data, artificial intelligence, and ICT. Although the synergy effects of these technologies will be great in various industrial ecosystems, drones are vulnerable to gusts such as "building wind" or "valley wind". Herein, the frequency domain of a mini drone was identified and a model-based disturbance observer (DOBs) was applied to implement the drone robust resistance against gusts. The frequency response of the Parrot Mambo or mini drone was measured with multi-sine excitation and the system dynamic parameters were identified. Based on the identified model, DOBs were designed and applied to the drone’s altitude, position, and yaw control. The effectiveness of the DOBs was verified with a sinusoidal disturbance. With the model-based DOB, 84.5% of the drone altitude responses, 50.7% of x responses, 52.1% of y responses, and 79.7% of yaw responses against sinusoidal disturbances were reduced. Flight responses were measured against wind disturbances with changing speed and direction. With the model-based DOBs, the drone"s altitude decreased by 87.7%, the x position by 53.0%, the y position by 60.6%, and the yaw angle by 56.2%.

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Control Performance Improvement of a Nonlinear Magnetic Levitation System with a Disturbance Observer: Yupeng Zheng, Hyeong-Joon Ahn; J. Korean Soc. Precis. Eng. 2023;40(4):329-334.
Published online April 1, 2023; DOI: https://doi.org/10.7736/JKSPE.022.133

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Magnetic levitation system (MLS) is a typical nonlinear system that controls the position of a steel ball with the magnetic force of the electromagnetic actuator. Since disturbances, due to various external forces and modeling errors, may cause excessive vibration or poor command following, disturbance suppression is necessary to improve the control performance of the MLS. This paper presents a control performance improvement approach of an MLS with a disturbance observer (DOB). First, a mathematical model of the MLS was introduced and validated with the measured frequency response. The MLS steel ball was levitated with a proportional–integral–derivative (PID) controller and a DOB was designed based on the physical model of the MLS. Both disturbance rejection and command tracking performances of the MLS with the DOB were investigated with several design parameters such as PID gains and Q filter. The disturbance rejection and command tracking performances were improved by 76.1% and 64.7%, respectively by using DOB. Finally, the disturbance rejection and command-following performances of the MLS with the DOB were verified experimentally. The effectiveness and limitations of DOB were explained with measured closed-loop frequency responses.

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Control Boost of a Magnetic Levitation System with Disturbance Observers
Yupeng Zheng, Hyeong-Joon Ahn
Journal of the Korean Society for Precision Engineering.2024; 41(4): 273. CrossRef

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Theoretic and Experimental Analysis to the Disturbance Torque Maintaining the Angle of Gimbal during the Centrifugal Acceleration Test: Jun Soo Kim, Dong-Kyun Lee, Suk-In Lee, Hyeon-Jun Cho, Moon-Young Yoon; J. Korean Soc. Precis. Eng. 2022;39(10):759-766.
Published online October 1, 2022; DOI: https://doi.org/10.7736/JKSPE.022.088

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In this study, the disturbance torque that maintains the gimbal at a specific angle during the centrifugal acceleration test was analyzed. Newton"s Second Law for Rotation was applied, to calculate the disturbance torque. A Theoretic solution for calculating the disturbance torque was derived, by separating the horizontal/vertical components of the moment of inertia. The Theoretic solution was verified, by numerical analysis (RecurDyn) of the simplified Gimbal model. To include the effect of acceleration, the distance between the central axis of the gimbal and the accelerated test equipment was applied as 0 and L (non-Zero). As a result of the analysis, it was found that the main disturbance torque is not related to acceleration, but to self-centrifugal force caused by rotation. A centrifugal acceleration test was conducted, to verify the operational performance of gimbal. The disturbance torque was calculated, by measuring the torque used to operate the gimbal"s motor. The result was compared with the disturbance torque, calculated by the Theoretic solution of the gimbal. The error between the result of test and Theoretic solution of torque was less than 4.5%.

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A study of Tuned Mass Damper (TMD) Application for Mass Imbalance and Vibration Reduction in Gimbal Systems for High-speed Maneuverable Vehicles
Jun-Soo Kim, Dong-Kyun Lee, Jong-Kuk Lee, Hyeon-Jun Cho, Ji-in Jung
Journal of the Korean Society for Precision Engineering.2024; 41(11): 857. CrossRef

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Design of a Super-Twisting Sliding Mode Controller with a Nonlinear Disturbance Observer for Precise Motion of a Ball-Screw Servo System: Seong Ik Han; J. Korean Soc. Precis. Eng. 2019;36(11):1017-1023.
Published online November 1, 2019; DOI: https://doi.org/10.7736/KSPE.2019.36.11.1017

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In this study, a super-twisting sliding mode controller with a non-linear disturbance observer for a ball-screw servo system was designed to obtain a precise motion and fast convergent control performance. Unknown dynamics of the servo system were approximated into pre-assumed diagonal constants for rapid controller design in the real industry to avoid expensive and time consuming experimental identification process. Moreover, uncertainties due to nonlinear friction, axis misalignment and dead zone were estimated by a nonlinear disturbance observer, which is combined with the designed super-twisting controller. The designed controller and observer systems were applied to the 2-axis ball screw servo system to verify the efficacy of the proposed control system via simulation and experiment.

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Adaptive Model Free Speed Control Algorithm of DC Motors Based on Recursive Least-Squares with Forgetting Factor: Kwang Seok Oh, Ja Ho Seo; J. Korean Soc. Precis. Eng. 2018;35(3):311-318.
Published online March 1, 2018; DOI: https://doi.org/10.7736/KSPE.2018.35.3.311

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This paper describes an adaptive model free speed control algorithm for DC motors, based on a recursive least-squares with forgetting factor. In order to control the speed of a DC motor, only the factors of output speed and voltage values have been used without a mathematical model of the DC motor. As the relationship between the input voltage and the DC motor speed in a specific region can be approximated as a first order system, the coefficient that represents the approximated first order system has been estimated by using a recursive least-squares approach with a forgetting factor model. Also, the error between the actual system and the approximated first order system has been estimated by a disturbance observer. Based on the estimated coefficient of the first order system, as well as this disturbance, an optimal input for tracking the desired velocity has been computed by using the Lyapunov direct method. Weighting factor adaptation rules have been proposed to enhance control performance. This performance evaluation has been conducted in a MATLAB/Simulink environment using a DC motor dynamic model for realistic evaluation. The evaluation results show that the developed adaptive DC motor speed control method ensures good tracking performance by using only the input voltage and the output speed information.

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Characteristics of Ankle Strategy Responses to Dynamic Tilting Perturbations: Hansol Seo, Hohyun Jung, Dukyoung Jung, Dohyung Lim; J. Korean Soc. Precis. Eng. 2018;35(2):203-210.
Published online February 1, 2018; DOI: https://doi.org/10.7736/KSPE.2018.35.2.203

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Maintaining balance is a factor critical and integral to our effective physical function as it relates to the normal activities of daily living. Of the “hip strategy”, “stepping strategy” and “ankle strategy”, it is known and accepted that the “ankle strategy” is the first activated parameter to assist in the maintenance of balance in motor output. However, few studies actually evaluated or assessed the precise attributes of “ankle strategy” in relation to any therapeutic effort tocorrect and/or rehabilitate from physical imbalance caused by dynamic tilting perturbation. The aim of the study was to identify precise characteristics of the “ankle strategy” as they respond to dynamic tilting perturbations. Seven healthy male (aged 25.5 ± 1.7 years, average height of 173.9 ± 6.4 cm, average body mass of 71.3 ± 6.5 kg) were recruited to participate. The ankle joint motions were subjected to eight dynamic tilting perturbations generated by the customized tilting perturbation simulator, and the responses were measured by 3D motion capture system. Concurrently, foot pressure distribution and the corresponding centers of pressure (COP) trajectory were measured by a pressure measuring system, and the four main muscles’ activations related to the ankle joint motions were measured by wireless electromyogram system.

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Estimation of Unmeasured Golf Swing of Arm Based on the Swing Dynamics
Changwon Lee, Sukyung Park
International Journal of Precision Engineering and Manufacturing.2018; 19(5): 745. CrossRef
Analysis of Contact Pressure at Knee Cartilage during Gait with Respect to Foot Progression Angle
Jeongro Yoon, Sungpil Ha, Seungju Lee, Soo-Won Chae
International Journal of Precision Engineering and Manufacturing.2018; 19(5): 761. CrossRef

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Analysis of Dynamic Balance Against Perturbation in Young and Elderly Subjects: Ji-Won Kim, Yu-Ri Kwon, Gwang-Moon Eom; J. Korean Soc. Precis. Eng. 2018;35(1):47-51.
Published online January 1, 2018; DOI: https://doi.org/10.7736/KSPE.2018.35.1.47

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The purpose of this study was to analyze dynamic postural balance against tilting perturbation in the young and the elderly. Twenty-eight young subjects and 22 elderly subjects participated in this study. Subjects performed dynamic balance test on a force plate during tilting perturbations (tilt-up and tilt-down). As outcome measures, peak distance and velocity were calculated from center of pressure (COP). Two-way ANOVA were performed for the outcome measures with the independent factors of age and gender. COP peak distance of the elderly was significantly greater than that of the young (p < 0.05). Velocity of COP showed age difference (p < 0.001) and also interaction effects only in tilt-up perturbation (p < 0.05). Especially, age-related difference existed in only women (p < 0.001). The age-related changing of women in the dynamic balance may be related to the greater fall rate of elderly women.

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Enhancing tool longevity through TiN coating in multistage cold forging: implementation and analysis using Archard’s wear theory and FEA
V. P. Kulkarni, S. M. Kulkarni, S. B. Patil, Aseem Anshul
International Journal on Interactive Design and Manufacturing (IJIDeM).2025; 19(12): 8773. CrossRef
Predicting Three-Dimensional Gait Parameters with a Single Camera Video Sequence
Jungbin Lee, Cong-Bo Phan, Seungbum Koo
International Journal of Precision Engineering and Manufacturing.2018; 19(5): 753. CrossRef

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The Adaptive Backstepping Controller of RBF Neural Network Which is Designed on the Basis of the Error: Hyun Woo Kim, Yook Hyun Yoon, Jin Han Jeong, Jahng Hyon Park; J. Korean Soc. Precis. Eng. 2017;34(2):125-131.
Published online February 1, 2017; DOI: https://doi.org/10.7736/KSPE.2017.34.2.125

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2-Axis Pan and Tilt Motion Platform, a complex multivariate non-linear system, may incur any disturbance, thus requiring system controller with robustness against various disturbances. In this study, we designed an adaptive backstepping compensated controller by estimating the disturbance and error using the Radial Basis Function Neural Network (RBF NN). In this process, Uniformly Ultimately Bounded (UUB) was demonstrated via Lyapunov and stability was confirmed. By generating progressive disturbance to the irregular frequency and amplitude changes, it was verified for various environmental disturbances. In addition, by setting the RBF NN input vector to the minimum, the estimated disturbance compensation process was analyzed. Only two input vectors facilitated compensatory function of RBF NN via estimating the modeling and control error values as well as irregular disturbance; the application of the process resulted in improved backstepping controller performance that was confirmed through simulation.

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A Study on I-PID-Based 2-DOF Snake Robot Head Control Scheme Using RBF Neural Network and Robust Term
Sung-Jae Kim, Jin-Ho Suh
Journal of Korea Robotics Society.2024; 19(2): 139. CrossRef
A Study on the Design of Error-Based Adaptive Robust RBF Neural Network Back-Stepping Controller for 2-DOF Snake Robot’s Head
Sung-Jae Kim, Maolin Jin, Jin-Ho Suh
IEEE Access.2023; 11: 23146. CrossRef