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"Actuator"

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This paper details the design and development of a robotic joint actuator that combines a frameless BLDC motor with a two-stage stepped planetary gear reducer, as well as a custom-built controller for precise position control. The rotor is physically coupled to a hollow sun gear shaft to facilitate internal cable routing, and the actuator features a high-resolution absolute encoder utilizing the BiSS-C protocol. The controller includes a 3-phase H-bridge driver, differential signal conversion for encoder communication, and a CAN interface for host communication. Position control is achieved through a PID loop operating at 1 kHz. A prototype actuator and controller have been fabricated, and step response tests were conducted. Experimental results indicate stable and accurate tracking of position commands, with a short settling time of 0.04773 seconds. These findings confirm the effectiveness of the integrated actuator system for robotic joint applications. Future work will focus on optimizing internal cable space and implementing sensorless control algorithms.
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Model-based Hysteresis and Cross-coupling Compensation for Precision Control of Piezoelectric Fast Steering Mirror
Hyo Geon Lee, Jae Woo Jung, Sang Won Jung, Jae Hyun Kim, Seonbin Lim, Youngjin Park, Jaehyun Lim, Kijun Seong, Daehee Lee, Seunggu Kang, No-Cheol Park, Jun Young Yoon
J. Korean Soc. Precis. Eng. 2026;43(2):139-149.
Published online February 1, 2026
DOI: https://doi.org/10.7736/JKSPE.025.091
This paper presents model-based hysteresis and cross-coupling compensators designed for precise control of a piezoelectric fast steering mirror (FSM). The hysteresis compensators are developed by inversely modeling the variation in the force constant relative to various excitation voltages, enabling the system to maintain linear response characteristics across a broad range of input amplitudes. The cross-coupling compensator is formulated by creating a decoupling matrix that cancels out coupling effects, generating signals of equal magnitude and opposite phase for each axis. The implementation of these compensators reduces the hysteresis band and magnitude uncertainty in the FSM dynamics by over 89.6% and 74.2%, respectively, while also significantly suppressing cross-coupling effects by more than 85.5%. Furthermore, the performance of the proposed compensators is validated in a closed-loop control system, demonstrating a notable reduction in cross-axis vibrations and improved tracking performance in response to step reference inputs and highfrequency sinusoidal trajectories.
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REGULAR

Design and Performance Test of Fast Steering Mirror
Byoung Ju Lee, Yong Hoon Lee, Hyeong Rae Kim, Ye Eun Bae, Sang Uk Nam, Jae Woo Jung, Sang Won Jung, Young Jin Park, Jun Young Yoon, No Cheol Park, Seoung Han Lee
J. Korean Soc. Precis. Eng. 2025;42(11):927-936.
Published online November 1, 2025
DOI: https://doi.org/10.7736/JKSPE.025.070

Currently, advanced countries such as the US and the UK are researching laser-based weapons and communication systems. The application of Fast Steering Mirror (FSM) is crucial in laser systems to control internal optical paths and compensate for disturbances, including atmospheric fluctuations and mechanical vibrations. Additionally, research is underway to enhance image clarity in surveillance and reconnaissance systems, such as Electro-Optical/Infrared (EO/IR) systems, by applying FSM technology. Consequently, the demand for FSMs is rising, necessitating the development of small, lightweight, and high-performance solutions. In this study, we designed a compact and lightweight FSM with a diameter of 25 mm, and its performance was validated through rigorous testing. Furthermore, we developed a piezoelectric actuator using single crystal piezoelectric material to ensure a wide operating bandwidth and rapid response speed for the FSM. Before manufacturing the designed FSM, we conducted modeling and simulation (M&S) to analyze its performance and confirm that it met the required specifications. Subsequently, a prototype of the FSM was produced, and its operating range, bandwidth, and accuracy were evaluated through performance tests.

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SPECIAL

Performance Study of Dielectric Elastomer Actuators with Varying Thickness of Carbon Nanotube Electrodes and Pre-stretch Ratios
Mingyu Kang, Joong-Hyun Park, Jong-An Choi, Jingu Jeong, Soonjae Pyo
J. Korean Soc. Precis. Eng. 2025;42(10):817-823.
Published online October 1, 2025
DOI: https://doi.org/10.7736/JKSPE.D.25.00004

This study examines how two key design parameters—the pre-stretch ratio and the thickness of the carbon nanotube (CNT) electrode—affect the actuation performance of dielectric elastomer actuators (DEAs). DEA samples are created with varying pre-stretch levels (50% and 125%) and different amounts of CNT spray coating (4 and 8 mg), and their threshold voltages and areal strains are quantitatively assessed. The experimental results indicate that higher pre-stretch ratios result in lower threshold voltages and greater areal deformations, while increased CNT thickness typically reduces actuator deformation due to enhanced mechanical stiffness. The combination of a high pre-stretch ratio and low CNT loading demonstrates improved electro-mechanical responsiveness at moderate voltages. These findings underscore the interconnected effects of structural and electrode design on DEA performance, offering practical design guidelines for optimizing soft actuator systems. This research lays a solid foundation for future applications of DEAs in haptic interfaces, wearable actuators, and soft robotics.

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Articles
Study on Hysteretic Characteristics of Piezoelectric Fast Steering Mirror in Frequency Response
Sang Won Jung, Hyo Geon Lee, Jae Woo Jung, Jae Hyun Kim, Seonbin Lim, Youngjin Park, Onemook Kim, Jaehyun Lim, Kijun Seong, Daehee Lee, Minjae Ko, No-Cheol Park, Jun Young Yoon
J. Korean Soc. Precis. Eng. 2024;41(11):913-920.
Published online November 1, 2024
DOI: https://doi.org/10.7736/JKSPE.024.116
Nonlinear hysteresis effects in piezoelectric fast steering mirrors (FSMs) are major culprits of deteriorating the servo performance and reducing the robustness of a control system. In order to compensate for such nonlinearities, this paper presents an identification and compensation method of piezoelectric hysteresis using frequency response measurements. The relationship between hysteresis curves and frequency response was analyzed using various amplitudes of input voltage and measured output displacements. Results proved that hysteresis curves could be reconstructed based on frequency response measurements. By utilizing an inverse function from reconstructed hysteresis curves, parameters for the compensation model were identified. Experimental results showed that the maximum range of output displacement at the nominal position due to hysteresis was significantly decreased by 76% when the hysteresis model identified by the proposed frequency-domain method was used. In addition, the compensated frequency response showed consistent results regardless of input amplitudes, implying that linear dynamics of the piezoelectric FSM could be separately measured.
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Dynamic Model of Fast Steering Mirror based on Piezoelectric Actuator
Yongsu Park, Geemin Lee, Dae Gyu Choi
J. Korean Soc. Precis. Eng. 2024;41(8):647-651.
Published online August 1, 2024
DOI: https://doi.org/10.7736/JKSPE.024.050
The fast steering mirror is now being used in industries beyond precision processing, such as space and defense. The piezoelectric fast steering mirror (PFSM), which utilizes a piezoelectric actuator, is particularly suitable for these industries as they often require devices like electro-optic devices to withstand external vibrations and impacts. While the PFSM has inherent high stiffness, its complex structure makes it difficult to control. To address this, an accurate dynamic model is necessary. In this paper, we derived a dynamic model for the PFSM using a two-inertial system model that takes into account its structural characteristics. This dynamic model consists of both a mechanical system model and an electrical system model. We measured the frequency response function from electrical input to mechanical output and compared it with the derived frequency response model to verify its accuracy. The derived model can be used not only for control design, but also for instrument design and interpretation.
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Research on Dry Cooling and Processing Precision in Ultra-precision Machining
Gyung-Il Lee
J. Korean Soc. Precis. Eng. 2023;40(11):929-936.
Published online November 1, 2023
DOI: https://doi.org/10.7736/JKSPE.023.112
Recently, with the development of the space, mobility, semiconductor, and precision machinery industries, the processing of precision mechanical parts has been recognized as an important and a high value-added technology. Research on ultra-precision processing is actively underway to produce such products. In addition, eco-friendliness and 0% carbon are emerging as key keywords in modern industrial society, and the need for this is also increasing in the ultra-precision processing field. As the industry advances, environmental issues are becoming a major concern, and in the processing technology field, environmental destruction caused by cutting oil is becoming an issue. To solve this problem, this study measured the movement precision of the global feed system and instaled a Fine Servo that corrects the nm-level movement of the feed system in real time, using a piezoelectric actuator, to finely drive the cutting tool to control the movement necessary for machining. We intended to control variables for ultra-precision machining and measure cutting heat generation in real time to establish a dry cooling method using thermoelectric elements without using cutting oil.
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Design, Fabrication, and Control of a Rotary Manipulator driven by Twisted Shape Memory Alloy (SMA) Wires
Gil-Yong Lee, Su-Yeon Lee
J. Korean Soc. Precis. Eng. 2023;40(8):665-673.
Published online August 1, 2023
DOI: https://doi.org/10.7736/JKSPE.023.039
The objective of this study was to present a rotary manipulating system driven by a rotary actuator based on twisted shape memory alloy (SMA) wires. The rotary actuator was composed of two oppositely twisted SMA wires connecting a rotor and a stator through a shaft. Two oppositely twisted SMA wires could generate bidirectional rotary motions upon actuation of each twisted SMA wire corresponding to the direction against the twist direction of each SMA wire. A manipulator was designed and fabricated by integrating manipulating arms, the rotary actuator, and a Hall effect magnetic rotary encoder which could measure the angular position of the rotary motion. We modeled and characterized the manipulator upon application of a ramp current input to each twisted SMA wire. A proportional-integral-derivative (PID) controller was designed and implemented to control the proposed rotary manipulator. Reference angular position tracking performances of the manipulator were evaluated with a series of experiments.

Citations

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  • Direct Ink Writing of Tungsten Planar Patterns by Extrusion-based Dispensing System
    Min-Hyeong Lee, Seung-Hyeon Choi, Jae-Wook Yu, Ji-Su Park, Hyuk-Chun Kwon, Ho-Chang Lee, Seong-Uk Oh, Seung-Gon Choi, In-Gu Choi, Gil-Yong Lee
    Journal of the Korean Society for Precision Engineering.2026; 43(1): 91.     CrossRef
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Design and Performance of a Pneumatic-Based Expanding Torsional Soft Spring Actuator
Jae Hyuck Jang, Ji Hun Kim, Seong Won Jang, Hugo Rodrigue
J. Korean Soc. Precis. Eng. 2022;39(11):811-817.
Published online November 1, 2022
DOI: https://doi.org/10.7736/JKSPE.022.046
The soft robotics field, known to have actuators and systems with a simple manufacturing process, being lightweight and safe to interact with humans, is in constant expansion. Present actuators have excessive unwanted deformations, which greatly affects the system"s performance by enlarging the external dimensions of the soft robot, reducing its efficiency, and causing unexpected or harmful contact with its surrounding environment. Thus, this work presented an actuator with a spring-like structure within a pneumatic chamber able to contract based on its innate design and lengthen when hyper-atmospheric pressures are applied, resulting in tension and torsion. A tensile testing machine and a force-torque sensor coupled with the actuator were used to evaluate its performance for different initial lengths, pressure inputs, and number of coils. At 30 kPa, a torque of up to 5 Nm was generated, have a maximum torsional angle of 41 degrees, and expanded 700% of its original length. Results have shown that the studied pneumatic-based expanding torsional soft spring actuator can stably lengthen under pneumatic pressure, resulting in sufficient force and considerable torque, and could be considered in future applications.
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Design and Fabrication of a Millimeter-Scale Rotary Actuator based on the Twisted Shape Memory Alloy (SMA) Wires
Eun-Jeong Jang, Su-Yeon Lee, Kyung-Hwan Kim, Gil-Yong Lee
J. Korean Soc. Precis. Eng. 2022;39(6):403-410.
Published online June 1, 2022
DOI: https://doi.org/10.7736/JKSPE.022.034
Shape memory alloy (SMA) has been widely used for many engineering and scientific applications, because it is largely deformable with high power density, and can be actuated easily by resistive heating. It is possible to reduce the size of the actuators by integrating or embedding SMA into the structures. While many applications have been reported regarding linear or bending actuators using the SMA wire, the development of a rotary actuator remains important and challenging for the engineering applications. Here, a new type of millimeter-scale rotary actuator is proposed based on the twisted SMA wires. SMA wires are twisted, folded, and integrated into the rotary actuator, and simple change of the twist direction enables the rotary actuator to rotate in the opposite direction. By integrating the oppositely twisted SMA wires into one rotary actuator unit, bidirectional rotary motions are possible. The actuation mechanism, design, and fabrication processes of the proposed rotary actuator are presented and demonstrated with its actuation performance. The fabricated actuators had average rotary working ranges from -38.68±4.92 deg to +45.37±8.79 deg in counterclockwise (CCW) and clockwise (CW) directions. This study will leverage the practical advances in the relevant engineering and scientific applications.

Citations

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  • A Novel Force-Couple SMA Rotary Actuator for MEMS Safety and Arming Device
    Yun Cao, Zeyi Chai, Yikang Huang, Mo Yang, Hengbo Zhu, Weirong Nie, Zhanwen Xi
    IEEE Sensors Journal.2025; 25(19): 35879.     CrossRef
  • Multi-field coupled dynamics for a movable tooth drive system integrated with shape memory alloys
    Lizhong Xu, Zhenglong Fu
    Heliyon.2023; 9(7): e17531.     CrossRef
  • Design, Fabrication, and Control of a Rotary Manipulator driven by Twisted Shape Memory Alloy (SMA) Wires
    Gil-Yong Lee, Su-Yeon Lee
    Journal of the Korean Society for Precision Engineering.2023; 40(8): 665.     CrossRef
  • Largely deformable torsional soft morphing actuator created by twisted shape memory alloy wire and its application to a soft morphing wing
    Su-Yeon Lee, Gil-Yong Lee
    Scientific Reports.2023;[Epub]     CrossRef
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Design and Evaluation of Soft Actuators Including Stretchable Conductive Fibers
Hye Won Lee, Yeji Han, Minchae Kang, Ju-Hee Lee, Min-Woo Han
J. Korean Soc. Precis. Eng. 2022;39(4):307-313.
Published online April 1, 2022
DOI: https://doi.org/10.7736/JKSPE.021.113
In this study, soft actuators comprising conductive fibers, flexible polymers, and shape memory alloys, which can be used as textile products, are introduced. Conductive fibers play an important role because they can be used as sensors in wearable devices. The conductive fiber introduced in this study is a form that can be combined with a polymer, and it comprises a form wrapped around a flexible polymer. When an electric current is applied to the shape memory alloy embedded in the polymer, macroscopic deformation occurs due to phase transformation from the Martensite to the Austenite phase. Conductive fibers used in soft actuators are affected by resistive heat generated by the shape memory alloy and bending deformation of the actuator. Accordingly, changes in the conduction properties of conductive fibers were observed due to bending deformation and temperature changes. We also fabricated soft actuators with different types of polymers and observed the differences. The soft actuator presented in this study is a one-piece combination of a conductor and an actuator using a textile-type conductor, and it is likely to be used in smart clothing applications.
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Hydraulic Manipulator to Assist Rescue Personnel
Maolin Jin, Sang Hyun Park, Jong Geol Kim, Ju Seong Shin, Junyoung Lee, Kap-Ho Seo, Jin-Ho Suh
J. Korean Soc. Precis. Eng. 2021;38(10):711-716.
Published online October 1, 2021
DOI: https://doi.org/10.7736/JKSPE.021.050
In this study, we developed a hydraulic manipulator to assist firefighters and rescue personnel at disaster sites. In the design procedure, we analyzed the manipulator considering the hydraulic actuators as well as the manipulator kinematics and dynamics. For the user interface, a macro/manual operation concept was proposed to provide an effective response in emergency and disaster situations. To cope with abnormalities of the disaster site operator, a protocol for switching local/remote operations was developed. The effectiveness of the hydraulic manipulator and operating system was verified through task implementation experiment.
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Development and Performance Evaluation of a Fine Stage for Compensating 6-DOF Motion Errors of an Ultra-Precision Linear Stage
Hoon-Hee Lee, In-Seok Lee, Kwang-Il Lee, Seung-Han Yang
J. Korean Soc. Precis. Eng. 2021;38(2):123-129.
Published online February 1, 2021
DOI: https://doi.org/10.7736/JKSPE.020.083
In ultra-precision processes, such as aerospace parts and precision mold machining, the accuracy of a feed drive system should be secured to achieve sufficient form accuracy. Dual-Servo stages, which compensate for multi-DOF motion errors, are being developed depending on the applied processes. This paper deals with the fine stage of a dual-servo stage to compensate for 6-DOF motion errors of a linear stage. The proposed fine stage measured 6-DOF errors of the linear stage motion with capacitive sensors, a reference mirror, and an optical encoder. It compensated for the errors using the flexure hinge mechanism with piezo actuators. The error equations and the inverse kinematics were derived to calculate the 6- DOF errors and displacements of piezo actuators for 6-DOF motions, respectively. Performance evaluation was implemented to verify feasibility of the developed fine stage of the fabricated dual-servo stage. Through the step response test of the fine stage, compensation resolutions for the translational and the rotational motion were confirmed to be less than 10 nm and 1/3 arcsec, respectively. The 6-DOF motion errors in the verification test were reduced by 73% on average.

Citations

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  • Study on Comparison of Friction Force between Ball- and Roller-LM Guides
    Hyeon Jeong Ra, Dong Wook Kim, Jun Man Lee, Han Seon Ryu, Jae Han Joung, Young Hun Jeong
    Journal of the Korean Society for Precision Engineering.2023; 40(11): 907.     CrossRef
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A Study on ECTS Control for Ultra-Precision Machining
Gyung-Il Lee
J. Korean Soc. Precis. Eng. 2020;37(9):699-705.
Published online September 1, 2020
DOI: https://doi.org/10.7736/JKSPE.020.034
In the framework of the 4th industrial revolution, modern machine-building rapidly converges with IOT technology. This requires very high precision machining of the parts and assemblies, such as electronics, vehicle and components, agricultural and construction machines, optical instruments, and machine tools. However, high precision machinery is quite expensive, and there exists a general need for low-cost equipment. While many researchers are working on this, their major focus is on cutting tools. This study aimed to compensate for errors and enhance machinery precision by adding a servo controller to the processing unit. Consequently, the study is on servo control and processing precision for processing utilizing ECTS (Error Compensation Tool Servo) to compensate for errors.
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Development of Lower-Limb Wearable Robot with Single Acting Hydraulic Telescopic Cylinder Electro Hydrostatic Actuator (SAT-EHA) for Handling of Heavy Loads
Dong-Hyun Jeong, Do-Yeon Kang, Ji-Seok Lee
J. Korean Soc. Precis. Eng. 2020;37(8):579-585.
Published online August 1, 2020
DOI: https://doi.org/10.7736/JKSPE.019.163
For years, crane, a chain block, an elevator and a forklift truck have been developed and used to carry heavy loads, but manpower needed where heavy equipment use is not practical. Aging workers suffer from musculoskeletal disorders, and are helped by developing various muscle assisting wearable robots. Industrial wearable robots must meet the payload capacity required for the pilot"s overall operation to ensure safety and operational performance. However, the payload capacity of wearable robot using rotary actuator or linear actuator at the knee joint decreases dramatically in the knee-flexion posture, with reduced moment arms. To solve this problem, the author recommends using Single Acting Hydraulic Telescopic Cylinder Electro Hydrostatic Actuator (SAT-EHA) to increase the torque of the knee in the knee flexion position. The characteristic of telescopic cylinder is high speed in 1st stage and high force in 2nd stage. The Human Universal Mobility Assist-Hybrid (HUMA-H) was developed by designing and fabricating the waist joint to balance the front and rear directions using an electric motor driver. As the payload capacity increases, the robot pilots can squat and stand up with heavy loads. The performance was verified through the operation test and respiratory gas analysis test of the manufactured HUMA-H.

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  • Development of Passive Upper Limb Exoskeleton Device (H-Frame) for Augment the Load Carrying Capability of the Human
    Dong-Hyun Jeong, Do Yeon Kang, Ji Seck Lee
    Journal of the Korean Society for Precision Engineering.2023; 40(4): 283.     CrossRef
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