Actuators

28 pages, 5287 KB

Open AccessArticle

Development Results of a Nitinol (NiTi) Angular Actuator

by Oana-Vasilica Grosu, Laurențiu-Dan Milici, Ciprian Bejenar and Mihaela Pavăl

Actuators 2025, 14(11), 546; https://doi.org/10.3390/act14110546 (registering DOI) - 8 Nov 2025

Shape memory alloys are key to sustainable technology and future industries, with one of the most remarkable materials at present being Nitinol (NiTi), which is known to have unique driving properties and applications, working in extreme conditions and capable of being applied in [...] Read more.

Shape memory alloys are key to sustainable technology and future industries, with one of the most remarkable materials at present being Nitinol (NiTi), which is known to have unique driving properties and applications, working in extreme conditions and capable of being applied in specific actuation tasks. In this context, this work presents an actuator prototype using versatile springs composed of nickel–titanium to produce angular displacements, beginning with contextual findings on the latest trends and opportunities for solutions in the field of Nitinol (NiTi) devices. Considering the research and industry concerns regarding shape memory materials and the need for research, design, and innovation in the development and investigation of various prototypes of Nitinol-based (NiTi) actuators, the functionalities, physical design, and static/dynamic performance of this newly proposed angular actuator offer strong potential. This work also presents and discusses the results of both experimental model testing and an analytical model simulation within MATLAB and Simulink R2022b. Full article

(This article belongs to the Section Actuator Materials)

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18 pages, 1253 KB

Open AccessArticle

Development of Closed Symmetrical Robotic Arms Driven by Pneumatic Muscle Actuators

by Che-Wei Chang and Mao-Hsiung Chiang

Actuators 2025, 14(11), 545; https://doi.org/10.3390/act14110545 (registering DOI) - 7 Nov 2025

Abstract

This research aims to investigate the practicality and feasibility of pneumatic muscle actuators (PMAs) applied in the pneumatic servo system. The mechanism consists of closed symmetrical planar robotic arms driven by two pairs of opposing PMAs, whose structure is similar to human arms. [...] Read more.

This research aims to investigate the practicality and feasibility of pneumatic muscle actuators (PMAs) applied in the pneumatic servo system. The mechanism consists of closed symmetrical planar robotic arms driven by two pairs of opposing PMAs, whose structure is similar to human arms. Importantly, the two distal links (or wrist parts) are combined into a collective end-effector, whose desired position is controlled only by the two shoulder angle joints. When two pairs of PMAs are attached to the upper arms, they actuate each shoulder and assist in the movement of the arms. However, the nonlinear behavior, high hysteresis, low damping, and time-varying characteristics of PMAs significantly limit their controllability. Therefore, to effectively address these challenges, a Fourier series-based adaptive sliding mode controller with H_∞ (FSB-ASMC + H_∞) is employed to achieve accurate path tracking of the PMAs. This control approach not only compensates for approximation errors, disturbances, and unmodeled dynamics but also ensures the desired H_∞ positioning performance of the overall system. The controller method can not only effectively prevent approximation errors, disturbances, and un-modeled dynamics but can also ensure the required H_∞ positioning performance of the whole system. Thus, the results of the experiment showed that the control strategy for the system collocating the FSB-ASMC + H_∞ can attain excellent control performance. Full article

(This article belongs to the Special Issue Intelligent Control for Pneumatic Servo System)

20 pages, 2461 KB

Open AccessArticle

Cooperative Systems Based on Arrays of Dielectric Elastomer Actuators

by Julian Neu, Sipontina Croce, Andrej Schagaew, Stefan Seelecke and Gianluca Rizzello

Actuators 2025, 14(11), 544; https://doi.org/10.3390/act14110544 (registering DOI) - 7 Nov 2025

Abstract

This work introduces two cooperative dielectric elastomer actuator (DEA) array designs, enabling comparison between a fully soft, wearable-oriented system and a rigid, high-performance platform. The soft silicone-based array achieves strokes up to 1.9 mm and maintains 44% displacement under strong bending, demonstrating suitability [...] Read more.

This work introduces two cooperative dielectric elastomer actuator (DEA) array designs, enabling comparison between a fully soft, wearable-oriented system and a rigid, high-performance platform. The soft silicone-based array achieves strokes up to 1.9 mm and maintains 44% displacement under strong bending, demonstrating suitability for haptic feedback in wearable applications. The rigid prototype, based on thermoformed buckling beams, provides strokes up to 2.8 mm, reduced hysteresis, improved stability, and reproducible fabrication, while allowing fine-tuning of preload conditions. Experiments revealed frequency-dependent coupling, enabling stimulation of defective actuators via neighboring elements and amplification of single-element strokes through cooperative excitation. Furthermore, self-sensing effects were exploited for error detection. These results underline the potential of DEA arrays for decentralized control, fault-tolerant actuation, and future applications in soft robotics and wearable systems. Full article

(This article belongs to the Section Actuator Materials)

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15 pages, 5396 KB

Open AccessArticle

An Adaptive Gripper for On-Orbit Grasping with Rapid Capture and Force Sensing Capabilities

by Qiong Wu, Yupeng Zhang, Wenfu Xu and Han Yuan

Actuators 2025, 14(11), 543; https://doi.org/10.3390/act14110543 - 7 Nov 2025

Abstract

End-effectors are becoming increasingly vital in orbital space missions, performing increasingly complex operational tasks. Current on-orbit missions primarily utilize net systems and rigid grippers as manipulators. However, the dynamic analysis of the net system is complicated, and its reliability is insufficient. Moreover, rigid [...] Read more.

End-effectors are becoming increasingly vital in orbital space missions, performing increasingly complex operational tasks. Current on-orbit missions primarily utilize net systems and rigid grippers as manipulators. However, the dynamic analysis of the net system is complicated, and its reliability is insufficient. Moreover, rigid grippers are not impact-resistant, which can lead to the target either rebounding or sustaining damage. This paper designs an adaptive gripper for rapid passive grasping. Adjusting the initial setup of the gripper by altering the cables allows for different degrees of trigger sensitivity to be achieved. The gripper presented in this paper integrates a bistable mechanism with a dual-mode actuation system, achieving performance metrics such as a

16.7 ms

activation time and a

5.42 m / s

capture speed. This combination of rapid passive and controllable active grasping demonstrates a novel and effective solution with significant potential for dynamic on-orbit service and debris removal missions. Full article

(This article belongs to the Special Issue Soft Robotics: Actuation, Control, and Application)

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17 pages, 2000 KB

Open AccessArticle

Mechanical Design and Kinematic Analysis of an Autonomous Wrist with DC Motor Actuators for Space Assembly

by Charles C. Nguyen, Ha T. T. Ngo, Tu T. C. Duong and Afshin Nabili

Actuators 2025, 14(11), 542; https://doi.org/10.3390/act14110542 - 7 Nov 2025

Abstract

This paper deals with the mechanical design and kinematic analysis of an autonomous wrist for space assembly (AWSA) whose actuators are activated by DC motors and ball screw drives. This robotic wrist was developed and built as a prototype to investigate in-space robotic [...] Read more.

This paper deals with the mechanical design and kinematic analysis of an autonomous wrist for space assembly (AWSA) whose actuators are activated by DC motors and ball screw drives. This robotic wrist was developed and built as a prototype to investigate in-space robotic operations, including maintaining and repairing spacecraft of the US National Aeronautics and Space Administration (NASA), such as the International Space Station (ISS) or satellites. Despite its disadvantages, such as a small workspace and low maneuverability, a parallel structure instead of a serial structure was selected for the design of the AWSA due to several advantages it has over a serial robot manipulator (SRM), including higher payload, greater stiffness, and better stability. The present paper also introduces a hybrid concept for robotic space operations, which combines an SRM performing gross motion and a parallel robot manipulator (PRM) performing fine motion. It then discusses the design and construction of the DC motor actuators and ball screw drives and presents the kinematic equations developed for the AWSA. This paper provides a closed-form solution to the inverse kinematics of the AWSA and a numerical solution using the Newton–Raphson method for its forward kinematics. Full article

(This article belongs to the Special Issue Actuators in Robotic Control—3rd Edition)

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21 pages, 2039 KB

Open AccessArticle

Experimental Study on the Characteristics of Dual Synthetic Jets Modulated by Driving Signals

by Shiqing Li, Shuxuan Cai, Lingwei Zeng and Zhenbing Luo

Actuators 2025, 14(11), 541; https://doi.org/10.3390/act14110541 - 6 Nov 2025

Abstract

Piezoelectric synthetic jet actuators typically struggle to generate high-speed jets at low driving frequencies due to the coupling effect between jet frequency and jet intensity. This limitation to some extent restricts their application in flow control within low-speed flow fields. To address this [...] Read more.

Piezoelectric synthetic jet actuators typically struggle to generate high-speed jets at low driving frequencies due to the coupling effect between jet frequency and jet intensity. This limitation to some extent restricts their application in flow control within low-speed flow fields. To address this issue, this study presents two methods of signal modulation. The effects of driving signal modulation on dual synthetic jet actuator (DSJA) characteristics were experimentally investigated. A laser displacement meter was used to measure the central point amplitude of the piezoelectric diaphragm, while the velocity at the exit of the DSJAs was measured using a hot-wire anemometer. The effects of signal modulation on the amplitude of the piezoelectric diaphragm, the maximum jet velocity, and the frequency domain characteristics of the dual synthetic jet (DSJ) were thoroughly analyzed. Experimental results demonstrate that driving signal modulation can enhance jet velocity at relatively low driving frequencies. The modulated DSJ exhibits low-frequency characteristics, rendering it suitable for flow control applications that require low-frequency jets. Furthermore, the coupling effect between jet frequency and jet intensity in the piezoelectric DSJA is significantly alleviated. Starting from the vibration displacement of the piezoelectric transducer (PZT), this paper systematically elaborates on the corresponding relationship between PZT displacement and the peak velocity at the jet outlet, and the “low-frequency and high-momentum jet generation method based on signal modulation” proposed herein is expected to break through the momentum–frequency coupling limitation of traditional piezoelectric dual-stenosis jet actuators (DSJAs) and enhance their application potential in low-speed flow control. Full article

(This article belongs to the Section Control Systems)

18 pages, 23476 KB

Open AccessArticle

Stress Analysis and Operational Limits of an SLA-Printed Soft Antagonistic Actuator Using a Yeoh-Calibrated Finite Element Model

by Jim S. Palacios-Lazo, Rosalba Galván-Guerra, Paola A. Niño-Suarez and Juan E. Velázquez-Velázquez

Actuators 2025, 14(11), 540; https://doi.org/10.3390/act14110540 - 6 Nov 2025

Abstract

Soft robotics has emerged as a promising approach for safe human–machine interaction, adaptive manipulation, and bioinspired motion, yet its progress relies on accurate material characterization and structural analysis of actuators. This study presents the mechanical behavior and stress analysis of a stereolithography-printed pneumatic [...] Read more.

Soft robotics has emerged as a promising approach for safe human–machine interaction, adaptive manipulation, and bioinspired motion, yet its progress relies on accurate material characterization and structural analysis of actuators. This study presents the mechanical behavior and stress analysis of a stereolithography-printed pneumatic actuator with antagonistic architecture, fabricated using Elastic 50A resin V2. Uniaxial tensile tests were performed according to ASTM D412 to derive material parameters, which were fitted to hyperelastic constitutive models. The Yeoh model was identified as the most accurate and implemented in finite element simulations to predict actuator deformation under multiple pressurization modes. Results revealed critical stress zones and established operational pressure limits of 110–130 kPa, beyond which the material approaches its tensile strength. Experimental testing with a controlled pneumatic system validated the numerical predictions, confirming both bending and multidirectional actuation as well as structural failure thresholds. The integration of material characterization, numerical modeling, and experimental validation provides a robust workflow for the design of SLA-fabricated antagonistic actuators. These findings highlight the advantages of combining digital fabrication with antagonistic actuation and material modeling to expand the understanding of soft robots’ behavior. Full article

(This article belongs to the Special Issue Soft Robotics: Actuation, Control, and Application)

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22 pages, 5209 KB

Open AccessArticle

Design of Static Output Feedback Active Suspension Controllers with Quarter-Car Model for Motion Sickness Mitigation

by Seongjin Yim

Actuators 2025, 14(11), 539; https://doi.org/10.3390/act14110539 - 6 Nov 2025

Abstract

This paper presents a method to design a static output feedback active suspension controller with a quarter-car model for motion sickness mitigation. To mitigate motion sickness in a vehicle, it has been known that the vertical acceleration and pitch rate of a sprung [...] Read more.

This paper presents a method to design a static output feedback active suspension controller with a quarter-car model for motion sickness mitigation. To mitigate motion sickness in a vehicle, it has been known that the vertical acceleration and pitch rate of a sprung mass should be reduced over the frequency range from 0.8 to 8 Hz. For this purpose, a half-car model has been used with linear quadratic optimal control for controller design because it can describe the pitch motion of a sprung mass. However, a controller design procedure with the half-car model is relatively more complex than the quarter-car one. To cope with this problem, a quarter-car model is used for controller design in this paper. The half-car model consists of two quarter-car models. Based on this fact, a controller designed with a quarter-car model can be applied to the front and rear suspensions in the half-car one. To avoid the full-state feedback in a real vehicle, a static output feedback structure is selected. To find the gains of the controllers for the quarter-car models in the front and rear suspensions, linear quadratic optimal control and a simulation-based optimization method are applied. To validate the proposed method, the controllers designed with the quarter-car and half-car models are simulated on a vehicle simulation package. From the simulation results, it is shown that the static output feedback active suspension controller designed with the quarter-car model is quite effective for motion sickness mitigation. Full article

(This article belongs to the Section Actuators for Surface Vehicles)

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19 pages, 10873 KB

Open AccessArticle

RM-Act 2.0: A Modular Harmonic Actuator Towards Improved Torque Density

by Ramesh Krishnan Muttathil Gopanunni, Alok Ranjan, Lorenzo Martignetti, Franco Angelini and Manolo Garabini

Actuators 2025, 14(11), 538; https://doi.org/10.3390/act14110538 - 6 Nov 2025

Abstract

In modern robotics, actuator performance is fundamental to achieving efficient and durable motion, with compactness and torque density being especially critical. Compact actuators enable integration in space-constrained systems without compromising functionality, while high torque density ensures powerful output relative to size, enhancing efficiency [...] Read more.

In modern robotics, actuator performance is fundamental to achieving efficient and durable motion, with compactness and torque density being especially critical. Compact actuators enable integration in space-constrained systems without compromising functionality, while high torque density ensures powerful output relative to size, enhancing efficiency and versatility. Harmonic gearboxes embody these qualities, offering lightweight design, zero backlash, and excellent torque density, which have made them a standard choice in robotics. However, their widespread adoption is limited by high manufacturing costs due to the precision machining required. To address this challenge, the authors previously introduced RM-Act, a Radial Modular Actuator employing two synchronous belts as harmonic speed reducers. Building on this concept, RM-Act 2.0 is introduced as an improved version that employs a single synchronous belt. This design reduces transmission slippage, improves torque density, and offers greater modularity with a wider range of reduction ratios. The work details the development and validation of RM-Act 2.0 through a functional prototype and performance model, highlighting its advancements over the original RM-Act in compactness and torque density. Full article

(This article belongs to the Section High Torque/Power Density Actuators)

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18 pages, 7247 KB

Open AccessArticle

Design and Research of a Neodymium Magnetic Ball Plug Ferrofluid Micropump

by Jie Su, Zhenggui Li, Baozhu Han, Qingsong Wang, Zhichao Qing and Qingyu Chen

Actuators 2025, 14(11), 537; https://doi.org/10.3390/act14110537 - 5 Nov 2025

Abstract

Due to the limitations of traditional micropumps in terms of miniaturization and integration, ferrofluid micropumps, as emerging microfluidic driving devices, exhibit significant application potential due to their unique pumping mechanism. Research on ferrofluid micropumps can advance micro/nano technology, meet biomedical needs, and facilitate [...] Read more.

Due to the limitations of traditional micropumps in terms of miniaturization and integration, ferrofluid micropumps, as emerging microfluidic driving devices, exhibit significant application potential due to their unique pumping mechanism. Research on ferrofluid micropumps can advance micro/nano technology, meet biomedical needs, and facilitate micro-electro-mechanical system (MEMS) integration. As traditional structural improvement methods struggle to meet increasingly stringent application conditions, under the action of the motion and mechanism of magnetic fluids, a new method of using neodymium magnetic ball plugs instead of traditional magnetic fluid plungers has been developed, aiming to enhance the pumping performance. In this study, the influence of the magnetic field (MF) generated by permanent magnets (PM) on the magnetic properties inside the micropump cavity was first determined. Furthermore, it was revealed in this research that the neodymium magnetic ball plug enhances the pumping flow rate and maximum pumping height of the ferrofluid plug and the pumping stability of the neodymium magnetic ball plug ferrofluid micropump is significantly improved. Additionally, the rotational speed (Rev) of the dynamic neodymium magnetic ball type magnetic fluid plug driven by the motor and the magnetic strength created by the PM are the main aspects influencing the result in this experiment. Full article

(This article belongs to the Section Miniaturized and Micro Actuators)

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19 pages, 6175 KB

Open AccessArticle

Design and Performance Analysis of a Subsea Wet-Mateable Connector Seal for Subsea Drilling Rigs

by Liang Xiong, Xiaolian Zhang, Shuo Zhao, Lieyu Tian, Bingyi Hu, Yang Lv, Jinsong Lu, Ailiyaer Ahemaiti, Zhaofei Sun, Fuyuan Li and Junguo Cui

Actuators 2025, 14(11), 536; https://doi.org/10.3390/act14110536 - 5 Nov 2025

Abstract

As terrestrial oil and gas resources continue to decline, deep-sea oil and gas development has become a strategic priority. A wide range of production equipment must be deployed on the seabed, among which subsea wet-mateable connectors are indispensable. To address the challenges of [...] Read more.

As terrestrial oil and gas resources continue to decline, deep-sea oil and gas development has become a strategic priority. A wide range of production equipment must be deployed on the seabed, among which subsea wet-mateable connectors are indispensable. To address the challenges of high pressure, low temperature, and corrosion in deep-sea environments, this study proposes a cooperative sealing strategy between the annular protrusion on the entry casing and a sliding sleeve. The leakage per single mate/demate cycle is quantified under varying insertion speeds and pressure differentials. By examining the effects of protrusion geometry, insertion speed, friction coefficient, and radial compression on sealing performance, the optimal parameters are identified: a friction coefficient of 0.15 and a trapezoidal-rib seal with 0.015 mm radial compression for dynamic sealing, yielding a contact pressure of 27.5 MPa and a mating/demating force of 197.26 N—satisfying the manipulation requirements of a remotely operated vehicle. Hydrostatic pressure tests demonstrate that the dynamic sealing design of the underwater connector achieves a balance between high reliability and low insertion resistance, and the prototype meets the operational requirements for deep-sea service. Full article

(This article belongs to the Section Control Systems)

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20 pages, 4340 KB

Open AccessArticle

Adaptive Prediction of Compressor Cylinder Pressure Dynamics Using a Physics-Guided VAE-CNN State Space Model

by Yingkang Lu, Buyun Sheng, Yanfei Li, Gaocai Fu, Shan Jiang and Zeyang Jiang

Actuators 2025, 14(11), 535; https://doi.org/10.3390/act14110535 - 5 Nov 2025

Abstract

Air compressor valves are prone to mechanical wear and elastic fatigue during long-term operation, often leading to poor sealing or leakage. Such leakage is a typical failure mode of reciprocating compressors, introducing strong nonlinearities into cylinder pressure dynamics and significantly increasing the difficulty [...] Read more.

Air compressor valves are prone to mechanical wear and elastic fatigue during long-term operation, often leading to poor sealing or leakage. Such leakage is a typical failure mode of reciprocating compressors, introducing strong nonlinearities into cylinder pressure dynamics and significantly increasing the difficulty of state monitoring. To address this issue, this paper presents an adaptive prediction method for compressor cylinder pressure dynamics under valve leakage failure, based on a physics-guided Variational Autoencoder Convolutional Neural Network State Space Model (VAE-CNN-SSM). In this framework, a VAE with embedded physical information is employed to construct the state equation and generate latent variables reflecting valve motion degradation, while a CNN-based observation equation is established to map latent states to cylinder pressure. This hybrid modeling strategy enables accurate prediction of cylinder pressure dynamics and effective characterization of valve degradation behaviors under valve leakage failure conditions. Comparative experiments against conventional models demonstrate that the proposed method achieves superior predictive accuracy, robustness, and generalization. These findings provide a new approach for analyzing valve leakage failures and offer technical support for condition monitoring, health management, and predictive maintenance of reciprocating compressors. Full article

(This article belongs to the Section High Torque/Power Density Actuators)

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23 pages, 4298 KB

Open AccessArticle

Study and Optimization of Shore-to-Ship Underwater Capacitive Power Transfer System Considering Parasitic Coupling

by Xin Pan, Haiyan Zeng, Guoli Feng, Shudan Wang and Enguo Rong

Actuators 2025, 14(11), 534; https://doi.org/10.3390/act14110534 - 5 Nov 2025

Abstract

The increasing trend towards electrification in transportation highlights the potential for electric ships and the demand for safe, rapid charging systems. Underwater capacitive power transfer (UCPT) is considered a suitable solution due to its high power density potential. This article presents research on [...] Read more.

The increasing trend towards electrification in transportation highlights the potential for electric ships and the demand for safe, rapid charging systems. Underwater capacitive power transfer (UCPT) is considered a suitable solution due to its high power density potential. This article presents research on and optimization of UCPT for shore-to-ship charging in freshwater environments. It proposes a design for an insulation coupler and explores the influence of parasitic capacitance in the environment. This study demonstrates how the ship and shore impact the coupler’s coupling coefficient and mutual capacitance, thereby affecting the power and efficiency. Through theoretical calculations and finite element analysis, a kW-level UCPT coupler is designed. Experimental verification under different cases confirms the efficiency and constant current output characteristics, with superior performance observed when the coupler is positioned further away from the ship or shore. This study showcases the potential of UCPT to provide reliable and efficient power supply for electric ships, while emphasizing the importance of considering environmental factors and parasitic effects in system design and operation. These findings contribute to advancing UCPT technology and offer insights for further optimization to enhance practical applicability. Full article

(This article belongs to the Special Issue Power Electronics and Actuators—Second Edition)

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25 pages, 4107 KB

Open AccessArticle

A Computational Framework for Formalizing Rollover Risk in Heavy-Duty Vehicles: Application to Concrete Truck Mixers

by Farshad Afshari and Daniel Garcia-Pozuelo

Actuators 2025, 14(11), 533; https://doi.org/10.3390/act14110533 - 3 Nov 2025

Abstract

This study introduces a computational framework that formalizes rollover risk in heavy-duty vehicles by integrating simulation-informed physical modeling with sensor-driven decision logic. The approach combines high-fidelity fluid–structure interaction modeling (via CFD) with multibody vehicle dynamics simulations to capture the complex behavior of rotating, [...] Read more.

This study introduces a computational framework that formalizes rollover risk in heavy-duty vehicles by integrating simulation-informed physical modeling with sensor-driven decision logic. The approach combines high-fidelity fluid–structure interaction modeling (via CFD) with multibody vehicle dynamics simulations to capture the complex behavior of rotating, partially filled mixer tanks under dynamic conditions. Rollover thresholds were identified by extracting the maximum safe speeds across a range of maneuvers (e.g., steady-state turning and step steering), using tire lift-off as the critical indicator. These thresholds were then formalized into decision rules using onboard sensor data, such as lateral acceleration, steering input, and tank rotation speed, allowing a real-time rollover warning system to continuously compare current vehicle states against critical limits. By systematically extracting critical force and moment responses and translating them into limit values provided by conventional onboard sensors (lateral acceleration, roll angle, steering input), the framework bridges high-fidelity simulation and real-time monitoring. A concrete truck mixer is used as a case study to demonstrate the utility of this approach in formalizing rollover thresholds for real-world decision support. Beyond the specific vehicle type, this work contributes to the broader discourse on how computational methods can contribute to new control or assistance strategies for safety-critical systems. Full article

(This article belongs to the Special Issue Feature Papers in Actuators for Surface Vehicles)

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19 pages, 860 KB

Open AccessArticle

Decentralized Disturbance Rejection Control of Triangularly Coupled Loop Thermosyphon System

by Novel Kumar Dey and Yan Wu

Actuators 2025, 14(11), 532; https://doi.org/10.3390/act14110532 - 1 Nov 2025

Abstract

In this paper, we investigate the stability of a triangularly coupled triple-loop thermosyphon system with momentum and heat exchange at the coupling point as well as the existence of disturbances. The controller consists of a single, local-state feedback. From the stability analysis, we [...] Read more.

In this paper, we investigate the stability of a triangularly coupled triple-loop thermosyphon system with momentum and heat exchange at the coupling point as well as the existence of disturbances. The controller consists of a single, local-state feedback. From the stability analysis, we obtain explicit bounds on the feedback gains, which depend on the Rayleigh numbers and the momentum coupling parameter, but independent of the thermal coupling parameter. The existence of the stability bounds allows us to design decentralized adaptive controllers to automatically search for the feasible gains when the system parameters are unknown. In the case of existing disturbances in the system, we approximate the disturbances via an extended-state observer for the purpose of disturbance rejection. Numerical results are given to demonstrate the performance of the proposed decentralized disturbance rejection controller design. Full article

(This article belongs to the Special Issue Active Disturbance Rejection Control: Theory, Design, and Applications in Advanced Actuation Systems)

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14 pages, 2912 KB

Open AccessArticle

Design of a Smart Foot–Ankle Brace for Tele-Rehabilitation and Foot Drop Monitoring

by Oluwaseyi Oyetunji, Austin Rain, William Feris, Austin Eckert, Abolghassem Zabihollah, Haitham Abu Ghazaleh and Joe Priest

Actuators 2025, 14(11), 531; https://doi.org/10.3390/act14110531 - 1 Nov 2025

Abstract

Foot drop, a form of paralysis affecting ankle and foot control, impairs walking and increases the risk of falls. Effective rehabilitation requires monitoring gait to guide personalized interventions. This study presents a proof-of-concept smart foot–ankle brace integrating low-cost sensors, including gyroscopes, accelerometers, and [...] Read more.

Foot drop, a form of paralysis affecting ankle and foot control, impairs walking and increases the risk of falls. Effective rehabilitation requires monitoring gait to guide personalized interventions. This study presents a proof-of-concept smart foot–ankle brace integrating low-cost sensors, including gyroscopes, accelerometers, and a Fiber Bragg Grating (FBG) array, with an Arduino-based processing platform. The system captures, in real time, the key locomotion parameters, namely, angular rotation, acceleration, and sole deformation. Experiments using a 3D-printed insole demonstrated that the device detects foot-drop-related gait deviations, with toe acceleration approximately twice that of normal walking. It also precisely detects foot deformation through FBG sensing. These results demonstrate the feasibility of the proposed system for monitoring gait abnormalities. Unlike commercial gait analysis devices, this work focuses on proof-of-concept development, providing a foundation for future improvements, including wireless integration, AI-based gait classification, and mobile application support for home-based or tele-rehabilitation applications. Full article

(This article belongs to the Special Issue Innovative MEMS: Merging Smart Materials with Electronic Techniques for Enhanced Sensing and Actuation)

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15 pages, 4862 KB

Open AccessArticle

Design and Analysis of a High-Speed Slotless Permanent Magnet Synchronous Motor Considering Air-Gap Airflow

by Hong-Jin Hu, Ze-Qiang Lin, Guang-Zhong Cao, Ming-Hong Guo and Su-Dan Huang

Actuators 2025, 14(11), 530; https://doi.org/10.3390/act14110530 - 31 Oct 2025

Abstract

The air-gap airflow significantly influences the performance of high-speed slotless permanent magnet synchronous motors (HSSPMSM), yet this critical factor is frequently overlooked during the design phase, resulting in performance deviations. This paper presents the design and multi-physical analysis of a 10 kW/40,000 rpm [...] Read more.

The air-gap airflow significantly influences the performance of high-speed slotless permanent magnet synchronous motors (HSSPMSM), yet this critical factor is frequently overlooked during the design phase, resulting in performance deviations. This paper presents the design and multi-physical analysis of a 10 kW/40,000 rpm HSSPMSM, explicitly accounting for air-gap airflow effects. A comprehensive coupling model integrating electromagnetic, thermal, mechanical, and airflow fields is established to guide the motor design. Based on this analysis, the motor dimensions and parameters are determined, and a prototype is fabricated. Experimental validation demonstrates that the developed HSSPMSM successfully meets the design specifications. Considering air-gap airflow can obtain more accurate thermal design results with an accuracy improvement of 6.8% compared to not considering air-gap airflow. The close agreement between the simulated and measured performance confirms the effectiveness of the proposed design methodology that incorporates airflow effects. Full article

(This article belongs to the Special Issue Magnetic Levitation and Actuator Integration: From Fundamental Research to Emerging Applications)

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21 pages, 5241 KB

Open AccessArticle

A Rigid–Flexible Coupling Gripper with High Grasping Adaptability

by Yigen Wu, Xuejia Huang, Yubo Hu, Bingnan Guo, Zikang Wu, Yuhang Chen, Xueqi Hu and Ruyi Du

Actuators 2025, 14(11), 529; https://doi.org/10.3390/act14110529 - 31 Oct 2025

Abstract

Nowadays, grippers are extensively employed to interact with dynamic and variable objects. Therefore, enhancing the adaptability of grippers is crucial for improving production efficiency and product quality. To address the trade-off between load capacity and interaction safety in rigid and soft grippers, this [...] Read more.

Nowadays, grippers are extensively employed to interact with dynamic and variable objects. Therefore, enhancing the adaptability of grippers is crucial for improving production efficiency and product quality. To address the trade-off between load capacity and interaction safety in rigid and soft grippers, this paper proposes a rigid–flexible coupling gripper with high grasping adaptability based on an underactuated structure. We conduct static analysis on the underactuated mechanism, followed by dimensional optimization using a genetic algorithm. After optimization, the grasping force error at each knuckle is reduced to 2 N, and the total grasping force reaches 38 N. The soft actuators, integrated with a rigid framework, not only increase the contact area during grasping but also mitigate the excessive concentration of contact forces, significantly improving the compliance of the gripper. Additionally, to tackle the issue of weak interfacial bonding strength caused by rigidity mismatch between rigid components and soft materials, this paper proposes a novel method of applying embedded microstructures to enhance the interfacial toughness of rigid–flexible coupling. The elastic deformation of these microstructures ensures strong interfacial connection strength both under tensile and shear stresses. Lastly, a robotic grasping platform is developed to carry out diverse grasping experiments. Experimental results show that the underactuated linkage mechanism and the flexible structure can collaboratively adjust grasping strategies when handling objects of various types, enabling stable manipulation while preventing object damage. This design effectively expands the operational applicability of the gripper. Full article

(This article belongs to the Special Issue Soft Robotics: Actuation, Control, and Application)

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27 pages, 2730 KB

Open AccessReview

Potential of Piezoelectric Actuation and Sensing in High Reliability Precision Mechanisms and Their Applications in Medical Therapeutics

by Adel Razek and Yves Bernard

Actuators 2025, 14(11), 528; https://doi.org/10.3390/act14110528 - 31 Oct 2025

Abstract

The present contribution aims to analyze and highlight the potential of piezoelectric materials in actuation and sensing duties, obtaining reliable high-precision outcomes in cutting-edge applications including medical interventions. This involves high-precision actuations of robotized procedures, as well as monitoring and controlling various physical [...] Read more.

The present contribution aims to analyze and highlight the potential of piezoelectric materials in actuation and sensing duties, obtaining reliable high-precision outcomes in cutting-edge applications including medical interventions. This involves high-precision actuations of robotized procedures, as well as monitoring and controlling various physical phenomena via structural sensing. The characteristics of these applications offer enhanced precision machinery and robotic tools, medical robotic precise interventions, and high-accuracy structural sensing. The paper exposed, analyzed, reviewed and discussed different subjects related to piezoelectric actuators, involving their displacement and positioning strategies, piezoelectric sensors, medical applications of piezoelectric actuators and sensors, including robotic actuation for medical interventions, and structural sensing in the monitoring of wearable healthcare tools. Discussions among others on the advantages and limitations of piezoelectric sensors and actuators in general, as well as future research perspectives in medical involvements, are also presented at the end of the article. The specific features in the illustrated applications reflect crucial behaviors in robotic actuation for medical interventions, structural sensing in the monitoring of healthcare wearable tools, and the control of various structural physical occurrences. Full article

(This article belongs to the Special Issue Actuator Technologies and Control: Materials, Devices and Applications)

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