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Editor’s Choice Articles

Editor’s Choice articles are based on recommendations by the scientific editors of MDPI journals from around the world. Editors select a small number of articles recently published in the journal that they believe will be particularly interesting to readers, or important in the respective research area. The aim is to provide a snapshot of some of the most exciting work published in the various research areas of the journal.

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21 pages, 1712 KiB  
Review
Fault Detection for Point Machines: A Review, Challenges, and Perspectives
by Xiaoxi Hu, Tao Tang, Lei Tan and Heng Zhang
Actuators 2023, 12(10), 391; https://doi.org/10.3390/act12100391 - 18 Oct 2023
Cited by 34 | Viewed by 6860
Abstract
Point machines are the actuators for railway switching and crossing systems that guide trains from one track to another. Hence, the safe and reliable behavior of point machines are pivotal for rail transportation. Recently, scholars and researchers have attempted to deploy various kinds [...] Read more.
Point machines are the actuators for railway switching and crossing systems that guide trains from one track to another. Hence, the safe and reliable behavior of point machines are pivotal for rail transportation. Recently, scholars and researchers have attempted to deploy various kinds of sensors on point machines for anomaly detection and/or incipient fault detection using date-driven algorithms. However, challenges arise when deploying condition monitoring and fault detection to trackside point machines in practical applications. This article begins by reviewing studies on fault and anomaly detection in point machines, encompassing employed methods and evaluation metrics. It subsequently conducts an in-depth analysis of point machines and outlines the envisioned intelligent fault detection system. Finally, it presents eight challenges and promising research directions along with a blueprint for intelligent point machine fault detection. Full article
(This article belongs to the Special Issue Electro-Mechanical Actuator, Diagnostic and Fault-Tolerant Control Systems)
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29 pages, 7081 KiB  
Review
Recent Advancements in Augmented Reality for Robotic Applications: A Survey
by Junling Fu, Alberto Rota, Shufei Li, Jianzhuang Zhao, Qingsheng Liu, Elisa Iovene, Giancarlo Ferrigno and Elena De Momi
Actuators 2023, 12(8), 323; https://doi.org/10.3390/act12080323 - 13 Aug 2023
Cited by 18 | Viewed by 8291
Abstract
Robots are expanding from industrial applications to daily life, in areas such as medical robotics, rehabilitative robotics, social robotics, and mobile/aerial robotics systems. In recent years, augmented reality (AR) has been integrated into many robotic applications, including medical, industrial, human–robot interactions, and collaboration [...] Read more.
Robots are expanding from industrial applications to daily life, in areas such as medical robotics, rehabilitative robotics, social robotics, and mobile/aerial robotics systems. In recent years, augmented reality (AR) has been integrated into many robotic applications, including medical, industrial, human–robot interactions, and collaboration scenarios. In this work, AR for both medical and industrial robot applications is reviewed and summarized. For medical robot applications, we investigated the integration of AR in (1) preoperative and surgical task planning; (2) image-guided robotic surgery; (3) surgical training and simulation; and (4) telesurgery. AR for industrial scenarios is reviewed in (1) human–robot interactions and collaborations; (2) path planning and task allocation; (3) training and simulation; and (4) teleoperation control/assistance. In addition, the limitations and challenges are discussed. Overall, this article serves as a valuable resource for working in the field of AR and robotic research, offering insights into the recent state of the art and prospects for improvement. Full article
(This article belongs to the Special Issue Motion Planning and Control of Robot Systems)
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20 pages, 11050 KiB  
Article
Towards Metaverse: Utilizing Extended Reality and Digital Twins to Control Robotic Systems
by Tero Kaarlela, Tomi Pitkäaho, Sakari Pieskä, Paulo Padrão, Leonardo Bobadilla, Matti Tikanmäki, Timo Haavisto, Víctor Blanco Bataller, Niko Laivuori and Mika Luimula
Actuators 2023, 12(6), 219; https://doi.org/10.3390/act12060219 - 24 May 2023
Cited by 12 | Viewed by 4347
Abstract
Digitalization shapes the ways of learning, working, and entertainment. The Internet, which enables us to connect and socialize is evolving to become the metaverse, a post-reality universe, enabling virtual life parallel to reality. In addition to gaming and entertainment, industry and academia have [...] Read more.
Digitalization shapes the ways of learning, working, and entertainment. The Internet, which enables us to connect and socialize is evolving to become the metaverse, a post-reality universe, enabling virtual life parallel to reality. In addition to gaming and entertainment, industry and academia have noticed the metaverse’s benefits and possibilities. For industry, the metaverse is the enabler of the future digital workplace, and for academia, digital learning spaces enable realistic virtual training environments. A connection bridging the virtual world with physical production systems is required to enable digital workplaces and digital learning spaces. In this publication, extended reality–digital twin to real use cases are presented. The presented use cases utilize extended reality as high-level user interfaces and digital twins to create a bridge between virtual environments and robotic systems in industry, academia, and underwater exploration. Full article
(This article belongs to the Special Issue Modeling, Optimization and Control of Robotic Systems)
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17 pages, 18565 KiB  
Article
Tendon-Driven Gripper with Variable Stiffness Joint and Water-Cooled SMA Springs
by Phuoc Thien Do, Quang Ngoc Le, Quoc Viet Luong, Hyun-Ho Kim, Hyeong-Mo Park and Yeong-Jin Kim
Actuators 2023, 12(4), 160; https://doi.org/10.3390/act12040160 - 4 Apr 2023
Cited by 14 | Viewed by 4307
Abstract
In recent years, there has been an increase in the development of medical robots to enhance interventional MRI-guided therapies and operations. Magnetic resonance imaging (MRI) surgical robots are particularly attractive due to their ability to provide excellent soft-tissue contrast during these procedures. This [...] Read more.
In recent years, there has been an increase in the development of medical robots to enhance interventional MRI-guided therapies and operations. Magnetic resonance imaging (MRI) surgical robots are particularly attractive due to their ability to provide excellent soft-tissue contrast during these procedures. This paper describes a novel design for a tendon-driven gripper that utilizes four shape memory alloy (SMA) spring actuators and variable stiffness joints controlled by SMA coils for use in MRI surgical robot applications. The contact force of the gripper link is determined by the mechanical properties of the SMA spring actuators (SSA) and the angle of each linkage, and the joint stiffness can be adjusted by varying the electrical current applied to the SMA coil. To enhance the efficiency of the SSAs, a new cooling system using water has been proposed and implemented. To validate the effectiveness of our proposed gripper, we conducted three types of experiments, namely, a single SSA experiment, a single SMA coil experiment, and a whole gripper experiment. The experimental results demonstrate that the proposed water-cooling system can effectively solve temperature issues of SMA, and the joint stiffness in the austenite state is higher than that in the martensite state. Moreover, our experiments show that the presented gripper is capable of grasping and holding objects of various shapes and weights. Full article
(This article belongs to the Section Actuators for Robotics)
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31 pages, 4558 KiB  
Review
A Comprehensive Review of 4D Printing: State of the Arts, Opportunities, and Challenges
by Faisal Khaled Aldawood
Actuators 2023, 12(3), 101; https://doi.org/10.3390/act12030101 - 25 Feb 2023
Cited by 27 | Viewed by 7133
Abstract
Over the past decade, 3D printing technology has been leading the manufacturing revolution. A recent development in the field of 3D printing has added time as a fourth dimension to obtain 4D printing parts. A fabricated design created by 3D printing is static, [...] Read more.
Over the past decade, 3D printing technology has been leading the manufacturing revolution. A recent development in the field of 3D printing has added time as a fourth dimension to obtain 4D printing parts. A fabricated design created by 3D printing is static, whereas a design created by 4D printing is capable of altering its shape in response to environmental factors. The phrase “4D printing” was introduced by Tibbits in 2013, and 4D printing has since grown in popularity. Different smart materials, stimulus, and manufacturing methods have been published in the literature to promote this new technology. This review paper provides a description of 4D printing technology along with its features, benefits, limitations, and drawbacks. This paper also reviews a variety of 4D printing applications in fields such as electronics, renewable energy, aerospace, food, healthcare, and fashion wear. The review discusses gaps in the research, the current challenges in 4D printing, and the future of 4D printing. Full article
(This article belongs to the Section Actuator Materials)
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14 pages, 3702 KiB  
Article
Origami-Inspired Soft Pneumatic Actuators: Generalization and Design Optimization
by Abdelrahman Zaghloul and Gary M. Bone
Actuators 2023, 12(2), 72; https://doi.org/10.3390/act12020072 - 9 Feb 2023
Cited by 13 | Viewed by 4214
Abstract
Soft actuators are essential to soft robots and can also be used with rigid-bodied robots. This paper is focused on methods for improving the applicability of origami-inspired soft pneumatic actuators (OSPA). Our method for rapidly fabricating OSPA is shown to be capable of [...] Read more.
Soft actuators are essential to soft robots and can also be used with rigid-bodied robots. This paper is focused on methods for improving the applicability of origami-inspired soft pneumatic actuators (OSPA). Our method for rapidly fabricating OSPA is shown to be capable of making a range of actuator sizes out of different materials. The largest OSPA has a force-to-weight ratio of 124, and can lift a 44 kg mass using a −85 kPa supply pressure. Experiments with a smaller OSPA demonstrate that it can perform 150,000 contraction/extension cycles while carrying a 2 kg mass with minimal degradation due to its materials and design. Compared to other OSPAs for which fatigue tests were reported, our accordion pattern OSPA has the best values of work-to-mass ratio, max. force, and fatigue life. A computationally efficient FEA-based constrained optimization method for maximizing an OSPA’s work output is then proposed. A 55% improvement in the work output was predicted, while validation experiments with OSPA prototypes showed a 53% improvement. While these improvement percentages are very similar, the values of the predicted stroke and work output are about 16% larger than the experimental values. The optimization requires only ~5 h to run on a common laptop. Full article
(This article belongs to the Special Issue Recent Advances in Pneumatic Soft Actuators)
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15 pages, 4720 KiB  
Article
Effect of the Crystal Structure on the Piezoelectricity of [001]-Textured (Na, K)(Nb, Sb)O3-SrZrO3-(Bi, Ag)ZrO3 Lead-Free Piezoelectric Thick Film
by Su-Hwan Go, Dae-Su Kim, Yeon-Gyeong Chae, Seok-June Chae, Eun-Ji Kim, Hyeon-Min Yu, Bum-Joo Kim, Seok-Jung Park, Joun-Ho Lee and Sahn Nahm
Actuators 2023, 12(2), 66; https://doi.org/10.3390/act12020066 - 3 Feb 2023
Cited by 10 | Viewed by 1823
Abstract
An amount of 3.0 mol% NaNbO3 seeds was used to align the grains of 0.96(Na0.5K0.5)(Nb0.93Sb0.07)O3-(0.04−x)SrZrO3-x(Bi0.5Ag0.5)ZrO3 [NKNS-(0.04−x)SZ-xBAZ] thick films (0.0 ≤ x ≤ 0.04) along the [...] Read more.
An amount of 3.0 mol% NaNbO3 seeds was used to align the grains of 0.96(Na0.5K0.5)(Nb0.93Sb0.07)O3-(0.04−x)SrZrO3-x(Bi0.5Ag0.5)ZrO3 [NKNS-(0.04−x)SZ-xBAZ] thick films (0.0 ≤ x ≤ 0.04) along the [001] direction. All the textured thick films had large Lotgering factors (>95%). The textured NKNS-0.02SZ-0.02BAZ thick film has a rhombohedral-orthorhombic-tetragonal (R-O-T) structure with a large proportion of the R-O structure (>80%) and nanodomains (0.7 nm in width and 6 nm in length). This thick film exhibited a large d33 value (760 ± 20 pC/N), kp value (0.58) and strain (0.16% at 4.0 kV/mm), with good temperature stability and fatigue properties. The high piezoelectricity of this thick film can be attributed to its high degree of texturing, optimized domain configuration, and the presence of nanodomains. The piezoelectric ceramic with a large d15/d33 value showed a large d33 value after [001] texturing because of the easy rotation of the spontaneous polarizations. Hence, the d15/d33 value can be used to select piezoelectric ceramics with large d33 values after [001] texturing. Full article
(This article belongs to the Special Issue Piezoelectric Actuators—A Special Issue in Honor of Prof. Dr. Kenji Uchino)
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32 pages, 32753 KiB  
Article
UAV Path Planning and Obstacle Avoidance Based on Reinforcement Learning in 3D Environments
by Guan-Ting Tu and Jih-Gau Juang
Actuators 2023, 12(2), 57; https://doi.org/10.3390/act12020057 - 28 Jan 2023
Cited by 22 | Viewed by 6544
Abstract
This study proposes using unmanned aerial vehicles (UAVs) to carry out tasks involving path planning and obstacle avoidance, and to explore how to improve work efficiency and ensure the flight safety of drones. One of the applications under consideration is aquaculture cage detection; [...] Read more.
This study proposes using unmanned aerial vehicles (UAVs) to carry out tasks involving path planning and obstacle avoidance, and to explore how to improve work efficiency and ensure the flight safety of drones. One of the applications under consideration is aquaculture cage detection; the net-cages used in sea-farming are usually numerous and are scattered widely over the sea. It is necessary to save energy consumption so that the drones can complete all cage detections and return to their base on land. In recent years, the application of reinforcement learning has become more and more extensive. In this study, the proposed method is mainly based on the Q-learning algorithm to enable improvements to path planning, and we compare it with a well-known reinforcement learning state–action–reward–state–action (SARSA) algorithm. For the obstacle avoidance control procedure, the same reinforcement learning method is used for training in the AirSim virtual environment; the parameters are changed, and the training results are compared. Full article
(This article belongs to the Special Issue Intelligent Control and Robotic System in Path Planning)
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21 pages, 8695 KiB  
Article
Impact Force Analysis in Inertia-Type Piezoelectric Motors
by Burhanettin Koc and Bülent Delibas
Actuators 2023, 12(2), 52; https://doi.org/10.3390/act12020052 - 26 Jan 2023
Cited by 15 | Viewed by 2552
Abstract
In an inertia-type motor, a piezoelectric multilayer actuator is espoused to a transient vibration velocity as high as 1.0 m/s during slip time. This vibration velocity makes the inertia-type motors dynamic but not quasi-static. We propose a kinetic model to describe the condition [...] Read more.
In an inertia-type motor, a piezoelectric multilayer actuator is espoused to a transient vibration velocity as high as 1.0 m/s during slip time. This vibration velocity makes the inertia-type motors dynamic but not quasi-static. We propose a kinetic model to describe the condition under which slippage can occur between a slider and a stator. The transient current absorbed by the multilayer actuators in a stator during slip time defines the slippage behavior of the slider. A new thickness-mode force factor expression (A33), which is a relation between the transient current and the transient vibration velocity, is described in electrical domain. Impact force acting on a friction coupler produced by the actuators in the stator is proportional to the rate of change in the transient current during the sliding time. Additionally, we present the structure and characteristics of a two-phase inertia-drive-type piezoelectric motor, on which the proposed model was evaluated. Driving the multilayer actuators with truncated and mirrored sawtooth signals enhances the system dynamics. As one actuator expands and the other shrinks, their respective hysteretic nonlinearities are canceled. The motor operating frequency can be as great as 30 kHz and typically load characteristics are unloaded velocity greater than 16.0 mm/s and generated force higher than 3.0 N. Full article
(This article belongs to the Special Issue Piezoelectric Actuators—A Special Issue in Honor of Prof. Dr. Kenji Uchino)
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18 pages, 6934 KiB  
Article
Flow Control around NACA0015 Airfoil Using a Dielectric Barrier Discharge Plasma Actuator over a Wide Range of the Reynolds Number
by Satoshi Sekimoto, Kozo Fujii, Masayuki Anyoji, Yuma Miyakawa, Shinichiro Ito, Satoshi Shimomura, Hiroyuki Nishida, Taku Nonomura and Takashi Matsuno
Actuators 2023, 12(1), 43; https://doi.org/10.3390/act12010043 - 16 Jan 2023
Cited by 11 | Viewed by 2791
Abstract
In this study, an experimental investigation of separation control using a dielectric barrier discharge plasma actuator was performed on an NACA0015 airfoil over a wide range of Reynolds numbers, angles of attack, and nondimensional burst frequencies. The range of the Reynolds number was [...] Read more.
In this study, an experimental investigation of separation control using a dielectric barrier discharge plasma actuator was performed on an NACA0015 airfoil over a wide range of Reynolds numbers, angles of attack, and nondimensional burst frequencies. The range of the Reynolds number was based on a chord length ranging from 2.52 × 105 to 1.008 × 106. A plasma actuator was installed at the leading edge and driven by AC voltage. Burst mode (duty-cycle) actuation was applied, with the nondimensional burst frequency ranging between 0.1–30. The control authority was evaluated using the time-averaged distribution of the pressure coefficient Cp and the calculated value of the lift coefficient Cl. The baseline flow fields were classified into three types: (1) leading-edge separation; (2) trailing-edge separation; and (3) the hysteresis between (1) and (2). The results of the actuated cases show that the control trends clearly depend on the differences in the separation conditions. In leading-edge separation, actuation with a burst frequency of approximately F+= 0.5 creates a wide negative pressure region on the suction-side surface, leading to an increase in the lift coefficient. In trailing-edge separation, several actuations alter the position of turbulent separation. Full article
(This article belongs to the Special Issue Dielectric Barrier Discharge Plasma Actuator for Active Flow Control)
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13 pages, 3357 KiB  
Article
Design of a Non-Back-Drivable Screw Jack Mechanism for the Hitch Lifting Arms of Electric-Powered Tractors
by Marco Claudio De Simone, Salvio Veneziano and Domenico Guida
Actuators 2022, 11(12), 358; https://doi.org/10.3390/act11120358 - 2 Dec 2022
Cited by 26 | Viewed by 3429
Abstract
The agricultural sector is constantly evolving. The rise in the world’s population generates an increasingly growing demand for food, resulting in the need for the agroindustry to meet this demand. Tractors are the vehicles that have made a real difference in agriculture’s development [...] Read more.
The agricultural sector is constantly evolving. The rise in the world’s population generates an increasingly growing demand for food, resulting in the need for the agroindustry to meet this demand. Tractors are the vehicles that have made a real difference in agriculture’s development throughout history, lowering costs in soil tillage and facilitating activities and operations for workers. This study aims to successfully design and build an autonomous, electric agricultural tractor that can autonomously perform recurring tasks in open-field and greenhouse applications. This project is fully part of the new industrial and agronomic revolution, known as Factory 4.0 and Agriculture 4.0. The predetermined functional requirements for the vehicle are its lightweight, accessible price, the easy availability of its spare parts, and its simple, ordinary maintenance. In this first study, the preliminary phases of sizing and conceptual design of the rover are reported before subsequently proceeding to the dynamical analysis. To optimize the design of the various versions of the automated vehicle, it is decided that a standard chassis would be built based on a robot operating inside a greenhouse on soft and flat terrains. The SimScape multi-body environment is used to model the kinematics of the non-back-drivable screw jack mechanism for the hitch-lifting arms. The control unit for the force exerted is designed and analyzed by means of an inverse dynamics simulation to evaluate the force and electric power consumed by the actuators. The results obtained from the analysis are essential for the final design of the autonomous electric tractor. Full article
(This article belongs to the Special Issue 10th Anniversary of Actuators)
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13 pages, 4912 KiB  
Article
Cable-Driven Parallel Robot Actuators: State of the Art and Novel Servo-Winch Concept
by Edoardo Idà and Valentina Mattioni
Actuators 2022, 11(10), 290; https://doi.org/10.3390/act11100290 - 11 Oct 2022
Cited by 17 | Viewed by 6325
Abstract
Cable-Driven Parallel Robots (CDPRs) use cables arranged in a parallel fashion to manipulate an end-effector (EE). They are functionally similar to several cranes that automatically collaborate in handling a shared payload. Thus, CDPRs share several types of equipment with [...] Read more.
Cable-Driven Parallel Robots (CDPRs) use cables arranged in a parallel fashion to manipulate an end-effector (EE). They are functionally similar to several cranes that automatically collaborate in handling a shared payload. Thus, CDPRs share several types of equipment with cranes, such as winches, hoists, and pulleys. On the other hand, since CDPRs rely on model-based automatic controllers for their operations, standard crane equipment may severely limit their performance. In particular, to achieve reasonably accurate feedback control of the EE pose during the process, the length of the cable inside the workspace of the robot should be known. Cable length is usually inferred by measuring winch angular displacement, but this operation is simple and accurate only if the winch transmission ratio is constant. This problem called for the design of novel actuation schemes for CDPRs; in this paper, we analyze the existing architectures of so-called servo-winches (i.e., servo-actuators which employ a rotational motor and have a constant transmission ratio), and we propose a novel servo-winch concept and compare the state-of-the-art architectures with our design in terms of pros and cons, design requirements, and applications. Full article
(This article belongs to the Special Issue Dynamics and Control of Robot Manipulators)
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28 pages, 1590 KiB  
Review
A Review on the Development of Pneumatic Artificial Muscle Actuators: Force Model and Application
by Bhaben Kalita, Alexander Leonessa and Santosha K. Dwivedy
Actuators 2022, 11(10), 288; https://doi.org/10.3390/act11100288 - 9 Oct 2022
Cited by 54 | Viewed by 12870
Abstract
Pneumatic artificial muscles (PAMs) are soft and flexible linear pneumatic actuators which produce human muscle like actuation. Due to these properties, the muscle actuators have an adaptable compliance for various robotic platforms as well as medical applications. While a variety of possible actuation [...] Read more.
Pneumatic artificial muscles (PAMs) are soft and flexible linear pneumatic actuators which produce human muscle like actuation. Due to these properties, the muscle actuators have an adaptable compliance for various robotic platforms as well as medical applications. While a variety of possible actuation schemes are present, there is still a need for the development of a soft actuator that is very light-weight, compact, and flexible with high power-to-weight ratio. To achieve this, the development of the PAM actuators has become an interesting topic for many researchers. In this review, the development of the different kinds of PAM available to date are presented along with manufacturing process and the operating principle. The various force models for artificial muscle presented in the literature are broadly reviewed with the constraints. Furthermore, the applications of PAM are included and classified based on the fields of biorobotics, medicine, and industry, along with advanced medical instrumentation. Finally, the needful improvements in terms of the dynamics of the muscle are discussed for the precise control of the PAMs as per the requirements for the applications. This review will be helpful for researchers working in the field of robotics and for designers to develop new type of artificial muscle depending on the applications. Full article
(This article belongs to the Special Issue Pneumatic Actuators for Robotics and Automation)
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11 pages, 6250 KiB  
Article
Stabilization of a Magnetic Repulsive Levitation Flywheel System Using a High-Efficiency Superconducting Magnetic Bearing
by Iwanori Murakami, Yiming Zhao and Tatuhiro Tashiro
Actuators 2022, 11(7), 180; https://doi.org/10.3390/act11070180 - 29 Jun 2022
Cited by 9 | Viewed by 3813
Abstract
In this study, we developed a superconducting magnetic bearing using a permanent repulsive magnet. A repulsive magnetic levitation system with a permanent magnet can generate a strong levitation force in the absence of a power supply. However, it is unstable, except in the [...] Read more.
In this study, we developed a superconducting magnetic bearing using a permanent repulsive magnet. A repulsive magnetic levitation system with a permanent magnet can generate a strong levitation force in the absence of a power supply. However, it is unstable, except in the direction of repulsion. In contrast, superconducting magnetic bearings can generate a restoring force in all directions by utilizing the magnetic flux pinning property of the superconductors. Therefore, we constructed a superconducting magnetic bearing (SMB), which is stable along all axes without control, and has a strong axial levitation force, by combining a repulsive-type magnetic levitation system and a superconducting magnetic levitation system. We also reduced the amount of HTS used for the SMB and proposed an efficient method of using HTS. Furthermore, a driving test of the flywheel incorporating the SMB was conducted to verify the characteristics of the SMB. The experiment confirmed that the flywheel could overcome the resonance and drive the flywheel. In the drive experiment, the flywheel was driven up to 10,000 rpm. Full article
(This article belongs to the Special Issue Advanced Technologies in Superconducting Actuators)
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18 pages, 4975 KiB  
Article
Data-Driven Kinematic Model of PneuNets Bending Actuators for Soft Grasping Tasks
by Ciprian Rad, Olimpiu Hancu and Ciprian Lapusan
Actuators 2022, 11(2), 58; https://doi.org/10.3390/act11020058 - 16 Feb 2022
Cited by 15 | Viewed by 4911
Abstract
The paper proposes a novel data-driven approximation kinematic (DAK) model to estimate the shape and opening level of a PneuNets soft gripper in relation to the applied pressure signal. The model offers suitable capabilities for implementing in real-time applications involving soft grasping planning [...] Read more.
The paper proposes a novel data-driven approximation kinematic (DAK) model to estimate the shape and opening level of a PneuNets soft gripper in relation to the applied pressure signal. The model offers suitable capabilities for implementing in real-time applications involving soft grasping planning and size recognition of fragile objects with different sizes and shapes. The proposed DAK model estimates the free bending behavior of a PneuNets actuator (soft gripper finger) based on a set of approximation functions derived from experimental data and an equivalent serial mechanism that mimics the shape of the actuator. The model was tested for a commercial PneuNets actuator with decreasing chamber height, produced by SoftGripping Co. (Hamburg, Germany). The model validation is accomplished through a set of experiments, where the shape and elementary displacements were measured using a digital image processing technique. The experimental data and the estimated data from the DAK model were compared and analyzed, respectively. The proposed approach has applicability in sensorless/self-sensing bending control algorithms of PneuNets actuators and in soft grasping applications where the robotic system must estimate the opening level of the gripper in order to be able to accomplish its task. Full article
(This article belongs to the Special Issue Soft and Compliant Actuators and Their Robotic Applications)
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15 pages, 5080 KiB  
Article
Manufacturing and Testing of a Variable Chord Extension for Helicopter Rotor Blades
by Christoph Balzarek, Steffen Kalow, Johannes Riemenschneider and Andres Rivero
Actuators 2022, 11(2), 53; https://doi.org/10.3390/act11020053 - 9 Feb 2022
Cited by 10 | Viewed by 2951
Abstract
Helicopters are still an indispensable addition to aviation in this day and age. They are characterized by their ability to master both forward flight and hover. These characteristics result in a wide range of possible operations. Key for the design of the rotor [...] Read more.
Helicopters are still an indispensable addition to aviation in this day and age. They are characterized by their ability to master both forward flight and hover. These characteristics result in a wide range of possible operations. Key for the design of the rotor blades is a blade design that always represents a compromise between the different flight conditions, which enables safe and efficient flight in the various flight conditions. In order to operate the rotor blade even more efficiently in all flight conditions, a new morphing concept, the so-called linear variable chord extension, has been developed. Here, the blade chord length in the root area is changed with the help of an elastic skin to adapt it to the respective flight condition. The simulations performed for this concept showed a promising increase in overall helicopter performance. The fabrication of the resulting demonstrator as well as the tests in the whirl-tower and wind tunnel are presented in this paper. The results of the tests show that the concept of linear variable chord extension has a positive influence and a great potential for hovering flight. Full article
(This article belongs to the Special Issue Design of Sensing and Actuation Systems)
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24 pages, 5966 KiB  
Review
Applications of Magnetorheological Fluid Actuator to Multi-DOF Systems: State-of-the-Art from 2015 to 2021
by Jong-Seok Oh, Jung Woo Sohn and Seung-Bok Choi
Actuators 2022, 11(2), 44; https://doi.org/10.3390/act11020044 - 1 Feb 2022
Cited by 27 | Viewed by 6419
Abstract
This review article presents various multi-DOF application systems that utilize smart magnetorheological (MR) fluid. It is well known that MR fluid has been actively studied and applied in many practical systems such as vehicle suspension dampers. The design requirements for the effective applications [...] Read more.
This review article presents various multi-DOF application systems that utilize smart magnetorheological (MR) fluid. It is well known that MR fluid has been actively studied and applied in many practical systems such as vehicle suspension dampers. The design requirements for the effective applications of MR fluid include geometry optimization, working principles, and control schemes. The geometry optimization is mostly related to the size minimization with high damping force, while the working principles are classified into the shear mode, the flow mode, and the squeeze mode depending on the dominant dynamic motion of the application system. The control schemes are crucial to achieve final targets such as robust vibration control against disturbances. It should be addressed that advanced output performances of MR application systems heavily depends on these three requirements. This review article presents numerous application systems such as sandwich structures, dampers, mounts, brakes, and clutches, which have been developed considering the three design requirements. In addition, in this article some merits and demerits of each application system are discussed to enable potential researchers to develop more effective and practical MR application systems featuring the multi-DOF dynamic motions. Full article
(This article belongs to the Special Issue Design and Application of Actuators with Multi-DOF Movement)
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17 pages, 8058 KiB  
Article
Visualization of the Electrohydrodynamic and Thermal Effects of AC-DBD Plasma Actuators of Plate- and Wire-Exposed Electrodes
by Yutaka Kaneko, Hiroyuki Nishida and Yoshiyuki Tagawa
Actuators 2022, 11(2), 38; https://doi.org/10.3390/act11020038 - 25 Jan 2022
Cited by 10 | Viewed by 4194
Abstract
The dielectric barrier discharge plasma actuator is a promising flow control device that uses surface discharge. The actuator generates an electrohydrodynamic force and Joule heating that contribute to the flow control. Thus, it is important to investigate the electrohydrodynamic and thermal effects on [...] Read more.
The dielectric barrier discharge plasma actuator is a promising flow control device that uses surface discharge. The actuator generates an electrohydrodynamic force and Joule heating that contribute to the flow control. Thus, it is important to investigate the electrohydrodynamic and thermal effects on the air flow. To this end, the flow velocity field, density field, and surface temperature distribution induced by an alternating current dielectric barrier discharge plasma actuator were experimentally examined, adopting particle image velocimetry, the background oriented schlieren technique, and an infrared camera. These experiments were conducted for plate- and wire-exposed electrode plasma actuators to investigate the effect of the shape of the exposed electrode. It was confirmed that the topology of the discharge is different between the two types of plasma actuators. This results in a difference in the spatial distributions of the velocity and density fields between the two actuators. In particular, we clarified that there is an obvious difference in the peak position of the density and temperature distribution between the two actuators. We also confirmed that the difference in the spatial distribution of the vertical velocity makes the above difference. Full article
(This article belongs to the Special Issue Dielectric Barrier Discharge Plasma Actuator for Active Flow Control)
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11 pages, 28380 KiB  
Article
Study on Properties of Potassium Sodium Niobate Coating Prepared by High Efficiency Supersonic Plasma Spraying
by Longlong Zhou, Xuewu Li, Dongyu He, Weiling Guo, Yanfei Huang, Gengchao He, Zhiguo Xing and Haidou Wang
Actuators 2022, 11(2), 28; https://doi.org/10.3390/act11020028 - 18 Jan 2022
Cited by 38 | Viewed by 3450
Abstract
In order to realize the construction of environmentally friendly potassium sodium niobate ceramic coating on metal surface, potassium sodium niobate ceramic coating was prepared by supersonic plasma spraying technology. The morphology, element extension and phase structure of such coating were investigated. The dielectric [...] Read more.
In order to realize the construction of environmentally friendly potassium sodium niobate ceramic coating on metal surface, potassium sodium niobate ceramic coating was prepared by supersonic plasma spraying technology. The morphology, element extension and phase structure of such coating were investigated. The dielectric and ferroelectric properties were also analyzed. The results show that the coating has good quality and tetragonal phase structure. When test frequency ≥ 2 MHz, the dielectric constant is stable at about 300, and also dielectric loss is stable at about 0.05. The coating exhibits good hysteresis loops under different applied electric fields. When the applied electric field is 16 KV/cm, residual polarization value of as-prepared coating reaches 17.02 μC·cm−2. Full article
(This article belongs to the Special Issue Shape Memory Alloys and Piezoelectric Materials and Their Applications)
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14 pages, 1654 KiB  
Article
An Enhanced Sliding Mode Speed Control for Induction Motor Drives
by Fahimeh Shiravani, Patxi Alkorta, Jose Antonio Cortajarena and Oscar Barambones
Actuators 2022, 11(1), 18; https://doi.org/10.3390/act11010018 - 10 Jan 2022
Cited by 18 | Viewed by 3629
Abstract
In this paper, an enhanced Integral Sliding Mode Control (ISMC) for mechanical speed of an Induction Motor (IM) is presented and experimentally validated. The design of the proposed controller has been done in the d-q synchronous reference frame and indirect Field Oriented Control [...] Read more.
In this paper, an enhanced Integral Sliding Mode Control (ISMC) for mechanical speed of an Induction Motor (IM) is presented and experimentally validated. The design of the proposed controller has been done in the d-q synchronous reference frame and indirect Field Oriented Control (FOC). Global asymptotic speed tracking in the presence of model uncertainties and load torque variations has been guaranteed by using an enhanced ISMC surface. Moreover, this controller provides a faster speed convergence rate compared to the conventional ISMC and the Proportional Integral methods, and it eliminates the steady-state error. Furthermore, the chattering phenomenon is reduced by using a switching sigmoid function. The stability of the proposed controller under parameter uncertainties and load disturbances has been provided by using the Lyapunov stability theory. Finally, the performance of this control method is verified through numerical simulations and experimental tests, getting fast dynamics and good robustness for IM drives. Full article
(This article belongs to the Special Issue New Control Schemes for Actuators)
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11 pages, 3777 KiB  
Article
Haptic Interface with Twin-Driven MR Fluid Actuator for Teleoperation Endoscopic Surgery System
by Takehito Kikuchi, Tetsumasa Takano, Akinori Yamaguchi, Asaka Ikeda and Isao Abe
Actuators 2021, 10(10), 245; https://doi.org/10.3390/act10100245 - 23 Sep 2021
Cited by 15 | Viewed by 3115
Abstract
Magnetorheological fluids (MRFs) are composite materials made of ferromagnetic particles, medium oils, and several types of additives. We have developed an actuation system for the fine haptic control of leader-follower robots. In this study, we developed a haptic interface with two link-type twin-driven [...] Read more.
Magnetorheological fluids (MRFs) are composite materials made of ferromagnetic particles, medium oils, and several types of additives. We have developed an actuation system for the fine haptic control of leader-follower robots. In this study, we developed a haptic interface with two link-type twin-driven MR fluid actuators and two MR fluid brakes for a teleoperation endoscopic surgery system and conducted evaluation tests for a remote operational task with a leader-follower robot system. For evaluations, we adopted the NASA-TLX questionnaire as a subjective assessment method. According to the experimental results, the total success rates were 0.462, 0.333, and 0.591, for the first haptic, middle no-haptic, and second haptic phases, respectively. The force information of the haptic forceps helped users to perceive grasping sensation on their fingers. Statistical analyses on the answers to the questionnaire indicate no significant differences. However, a decreasing tendency in the mental stress in the complicated manipulation tasks for fragile objects is observed. Full article
(This article belongs to the Special Issue Smart Materials for Smart Actuators and Semi-active Components)
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21 pages, 8072 KiB  
Article
Intelligent Vehicle Lateral Control Method Based on Feedforward + Predictive LQR Algorithm
by Tao Yang, Ziwen Bai, Zhiqiang Li, Nenglian Feng and Liqing Chen
Actuators 2021, 10(9), 228; https://doi.org/10.3390/act10090228 - 9 Sep 2021
Cited by 45 | Viewed by 5438
Abstract
Aiming at the problems of control stability of the intelligent vehicle lateral control method, single test conditions, etc., a lateral control method with feedforward + predictive LQR is proposed, which can better adapt to the problem of intelligent vehicle lateral tracking control under [...] Read more.
Aiming at the problems of control stability of the intelligent vehicle lateral control method, single test conditions, etc., a lateral control method with feedforward + predictive LQR is proposed, which can better adapt to the problem of intelligent vehicle lateral tracking control under complex working conditions. Firstly, the vehicle dynamics tracking error model is built by using the two degree of freedom vehicle dynamics model, then the feedforward controller, predictive controller and LQR controller are designed separately based on the path tracking error model, and the lateral control system is built. Secondly, based on the YOLO-v3 algorithm, the environment perception system under the urban roads is established, and the road information is collected, the path equation is fitted and sent to the control system. Finally, the joint simulation is carried out based on CarSim software and a Matlab/Simulink control model, and tested combined with hardware in the loop test platform. The results of simulation and hardware-in-loop test show that the transverse controller with feedforward + predictive LQR can effectively improve the accuracy of distance error control and course error control compared with the transverse controller with feedforward + LQR control, LQR controller and MPC controller on the premise that the vehicle can track the path in real time. Full article
(This article belongs to the Section Actuators for Land Transport)
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26 pages, 62480 KiB  
Review
Soft Exoskeletons: Development, Requirements, and Challenges of the Last Decade
by Alan Francisco Pérez Vidal, Jesse Yoe Rumbo Morales, Gerardo Ortiz Torres, Felipe de Jesús Sorcia Vázquez, Alan Cruz Rojas, Jorge Aurelio Brizuela Mendoza and Julio César Rodríguez Cerda
Actuators 2021, 10(7), 166; https://doi.org/10.3390/act10070166 - 19 Jul 2021
Cited by 56 | Viewed by 11201
Abstract
In this article, various investigations on soft exoskeletons are presented and their functional and structural characteristics are analyzed. The present work is oriented to the studies of the last decade and covers the upper and lower joints, specifically the shoulder, elbow, wrist, hand, [...] Read more.
In this article, various investigations on soft exoskeletons are presented and their functional and structural characteristics are analyzed. The present work is oriented to the studies of the last decade and covers the upper and lower joints, specifically the shoulder, elbow, wrist, hand, hip, knee, and ankle. Its functionality, applicability, and main characteristics are exposed, such as degrees of freedom, force, actuators, power transmission methods, control systems, and sensors. The purpose of this work is to show the current trend in the development of soft exoskeletons, in addition to specifying the essential characteristics that must be considered in its design and the challenges that its construction implies. Full article
(This article belongs to the Special Issue Actuators on Soft Exoskeletons)
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14 pages, 4171 KiB  
Article
Data-Driven Tuning of PID Controlled Piezoelectric Ultrasonic Motor
by Sarah Makarem, Bülent Delibas and Burhanettin Koc
Actuators 2021, 10(7), 148; https://doi.org/10.3390/act10070148 - 29 Jun 2021
Cited by 27 | Viewed by 5660
Abstract
Ultrasonic motors employ resonance to amplify the vibrations of piezoelectric actuator, offering precise positioning and relatively long travel distances and making them ideal for robotic, optical, metrology and medical applications. As operating in resonance and force transfer through friction lead to nonlinear characteristics [...] Read more.
Ultrasonic motors employ resonance to amplify the vibrations of piezoelectric actuator, offering precise positioning and relatively long travel distances and making them ideal for robotic, optical, metrology and medical applications. As operating in resonance and force transfer through friction lead to nonlinear characteristics like creep and hysteresis, it is difficult to apply model-based control, so data-driven control offers a good alternative. Data-driven techniques are used here for iterative feedback tuning of a proportional integral derivative (PID) controller parameters and comparing between different motor driving techniques, single source and dual source dual frequency (DSDF). The controller and stage system used are both produced by the company Physik Instrumente GmbH, where a PID controller is tuned with the help of four search methods: grid search, Luus–Jaakola method, genetic algorithm, and a new hybrid method developed that combines elements of grid search and Luus–Jaakola method. The latter method was found to be quick to converge and produced consistent result, similar to the Luus–Jaakola method. Genetic Algorithm was much slower and produced sub optimal results. The grid search has also proven the DSDF driving method to be robust, less parameter dependent, and produces far less integral position error than the single source driving method. Full article
(This article belongs to the Special Issue Piezoelectric and Electrostrictive Materials in Mechatronics, Precision Engineering and Vibration Control)
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26 pages, 6749 KiB  
Review
Current Trends and Prospects in Compliant Continuum Robots: A Survey
by Shiyao Li and Guangbo Hao
Actuators 2021, 10(7), 145; https://doi.org/10.3390/act10070145 - 28 Jun 2021
Cited by 42 | Viewed by 7326
Abstract
Compliant continuum robots (CCRs) have slender and elastic bodies. Compared with a traditional serial robot, they have more degrees of freedom and can deform their flexible bodies to go through a constrained environment. In this paper, we classify CCRs according to basic transmission [...] Read more.
Compliant continuum robots (CCRs) have slender and elastic bodies. Compared with a traditional serial robot, they have more degrees of freedom and can deform their flexible bodies to go through a constrained environment. In this paper, we classify CCRs according to basic transmission units. The merits, materials and potential drawbacks of each type of CCR are described. Drive systems depend on the basic transmission units significantly, and their advantages and disadvantages are reviewed and summarized. Variable stiffness and intrinsic sensing are desired characteristics of CCRs, and the methods of obtaining the two characteristics are discussed. Finally, we discuss the friction, buckling, singularity and twisting problems of CCRs, and emphasise the ways to reduce their effects, followed by several proposing perspectives, such as the collaborative CCRs. Full article
(This article belongs to the Special Issue Soft and Compliant Actuators and Their Robotic Applications)
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19 pages, 2635 KiB  
Article
Improved Sliding Mode-Active Disturbance Rejection Control of Electromagnetic Linear Actuator for Direct-Drive System
by Yingtao Lu, Cao Tan, Wenqing Ge, Bo Li and Jiayu Lu
Actuators 2021, 10(7), 138; https://doi.org/10.3390/act10070138 - 22 Jun 2021
Cited by 18 | Viewed by 3351
Abstract
The electromagnetic linear actuator is used as the core drive unit to achieve high precision and high response in the direct-drive actuation system. In order to improve the response performance and control accuracy of the linear drive unit, an improved sliding mode-active disturbance [...] Read more.
The electromagnetic linear actuator is used as the core drive unit to achieve high precision and high response in the direct-drive actuation system. In order to improve the response performance and control accuracy of the linear drive unit, an improved sliding mode-active disturbance rejection control (ISM-ADRC) method was proposed. A motor model was established based on improved LuGre dynamic friction. The position loop adopts the improved integral traditional sliding mode control based on an extended state observer, and the current loop adopts PI control. The stability of the system is verified based on the Lyapunov theory. A nonlinear dilated state observer is used to effectively observe the electromagnetic linear actuator position and velocity information while estimating and compensating the internal and external uncertainty perturbations. At the same time, the saturation function sat(s) is used to replace the sign(s) and introduce the power function of the displacement error variable. The improved integral sliding mode control law further improves the response speed and control accuracy of the controller while reducing the jitter inherent in the conventional sliding mode. Simulation and experimental data show that the proposed improved sliding mode-active disturbance rejection control reduces the 8-mm step response time of the electromagnetic linear actuator by 21.9% and the steady-state error by less than 0.01 mm compared with the conventional sliding-mode control, while the system has 49.4% less adjustment time for abrupt load changes and is more robust to different loads and noise. Full article
(This article belongs to the Section Actuators for Land Transport)
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16 pages, 1847 KiB  
Article
Effects of Ferroelectric Fillers on Composite Dielectric Elastomer Actuator
by Stanislav Sikulskyi, Danayit T. Mekonnen, Abdullah El Atrache, Eduardo Divo and Daewon Kim
Actuators 2021, 10(7), 137; https://doi.org/10.3390/act10070137 - 22 Jun 2021
Cited by 17 | Viewed by 3725
Abstract
Integrating nano- to micro-sized dielectric fillers to elastomer matrices to form dielectric composites is one of the commonly utilized methods to improve the performance of dielectric elastomer actuators (DEAs). Barium titanate (BaTiO3) is among the widely used ferroelectric fillers for this [...] Read more.
Integrating nano- to micro-sized dielectric fillers to elastomer matrices to form dielectric composites is one of the commonly utilized methods to improve the performance of dielectric elastomer actuators (DEAs). Barium titanate (BaTiO3) is among the widely used ferroelectric fillers for this purpose; however, calcium copper titanate CaCu3Ti4O12 (CCTO) has the potential to outperform such conventional fillers. Despite their promising performance, CCTO-based dielectric composites for DEA application are studied to a relatively lower degree. Particularly, the composites are characterized for a comparably small particle loading range, while critical DEA properties such as breakdown strength and nonlinear elasticity are barely addressed in the literature. Thus, in this study, CCTO was paired with polydimethylsiloxane (CH3)3SiO[Si(CH3)2O]nSi(CH3)3 (PDMS), Sylgard 184, to gain a comprehensive understanding of the effects of particle loading and size on the dielectric composite properties important for DEA applications. The dielectric composites’ performance was described through the figures of merit (FOMs) that consider materials’ Young’s modulus, dielectric permittivity, and breakdown strength. The optimum amounts of the ferroelectric filler were determined through the FOMs to maximize composite DEA performance. Lastly, electromechanical testing of the pre-stretched CCTO-composite DEA validated the improved performance over the plain elastomer DEA, with deviations from prediction attributed to the studied composites’ nonlinearity. Full article
(This article belongs to the Special Issue Electroactive Polymer Actuators)
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22 pages, 2401 KiB  
Article
Control of a Rehabilitation Robotic Device Driven by Antagonistic Soft Actuators
by Haozhen Chi, Hairong Su, Wenyu Liang and Qinyuan Ren
Actuators 2021, 10(6), 123; https://doi.org/10.3390/act10060123 - 7 Jun 2021
Cited by 9 | Viewed by 4213
Abstract
Stroke is becoming a widely concerned social problem, and robot-assisted devices have made considerable contributions in the training and treatment of rehabilitation. Due to the compliance and continuous deformation capacity, rehabilitation devices driven by soft actuators are attached to widespread attention. Considering the [...] Read more.
Stroke is becoming a widely concerned social problem, and robot-assisted devices have made considerable contributions in the training and treatment of rehabilitation. Due to the compliance and continuous deformation capacity, rehabilitation devices driven by soft actuators are attached to widespread attention. Considering the large output force of pneumatic artificial muscle (PAM) and the biological musculoskeletal structure, an antagonistic PAM-driven rehabilitation robotic device is developed. To fulfill the need for control of the proposed device, a knowledge-guided data-driven modeling approach is used and an adaptive feedforward–feedback control approach is presented to ensure the motion accuracy under large deformation motion with high frequency. Finally, several simulations and experiments are carried out to evaluate the performance of the developed system, and the results show that the developed system with the proposed controller can achieve expected control performance under various operations. Full article
(This article belongs to the Special Issue Robot Control in Human-Machine Systems)
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23 pages, 9501 KiB  
Review
Review of Magnetoelectric Sensors
by Junqi Gao, Zekun Jiang, Shuangjie Zhang, Zhineng Mao, Ying Shen and Zhaoqiang Chu
Actuators 2021, 10(6), 109; https://doi.org/10.3390/act10060109 - 24 May 2021
Cited by 53 | Viewed by 6614
Abstract
Multiferroic magnetoelectric (ME) materials with the capability of coupling magnetization and electric polarization have been providing diverse routes towards functional devices and thus attracting ever-increasing attention. The typical device applications include sensors, energy harvesters, magnetoelectric random access memories, tunable microwave devices and ME [...] Read more.
Multiferroic magnetoelectric (ME) materials with the capability of coupling magnetization and electric polarization have been providing diverse routes towards functional devices and thus attracting ever-increasing attention. The typical device applications include sensors, energy harvesters, magnetoelectric random access memories, tunable microwave devices and ME antennas etc. Among those application scenarios, ME sensors are specifically focused in this review article. We begin with an introduction of materials development and then recent advances in ME sensors are overviewed. Engineering applications of ME sensors are followed and typical scenarios are presented. Finally, several remaining challenges and future directions from the perspective of sensor designs and real applications are included. Full article
(This article belongs to the Special Issue Advances in Piezoelectric Actuators 2022)
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11 pages, 1950 KiB  
Article
A Sensorized Soft Pneumatic Actuator Fabricated with Extrusion-Based Additive Manufacturing
by Antonia Georgopoulou, Lukas Egloff, Bram Vanderborght and Frank Clemens
Actuators 2021, 10(5), 102; https://doi.org/10.3390/act10050102 - 10 May 2021
Cited by 37 | Viewed by 6010
Abstract
Soft pneumatic actuators with a channel network (pneu-net) based on thermoplastic elastomers are compatible with fused deposition modeling (FDM). However, conventional filament-based fused deposition modeling (FDM) printers are not well suited for thermoplastic elastomers with a shore hardness (Sh < 70A). Therefore, in [...] Read more.
Soft pneumatic actuators with a channel network (pneu-net) based on thermoplastic elastomers are compatible with fused deposition modeling (FDM). However, conventional filament-based fused deposition modeling (FDM) printers are not well suited for thermoplastic elastomers with a shore hardness (Sh < 70A). Therefore, in this study, a pellet-based FDM printer was used to print pneumatic actuators with a shore hardness of Sh18A. Additionally, the method allowed the in situ integration of soft piezoresistive sensing elements during the fabrication. The integrated piezoresistive elements were based on conductive composites made of three different styrene-ethylene-butylene-styrene (SEBS) thermoplastic elastomers, each with a carbon black (CB) filler with a ratio of 1:1. The best sensor behavior was achieved by the SEBS material with a shore hardness of Sh50A. The dynamic and quasi-static sensor behavior were investigated on SEBS strips with integrated piezoresistive sensor composite material, and the results were compared with TPU strips from a previous study. Finally, the piezoresistive composite was used for the FDM printing of soft pneumatic actuators with a shore hardness of 18 A. It is worth mentioning that 3 h were needed for the fabrication of the soft pneumatic actuator with an integrated strain sensing element. In comparison to classical mold casting method, this is faster, since curing post-processing is not required and will help the industrialization of pneumatic actuator-based soft robotics. Full article
(This article belongs to the Special Issue 3D Printable Soft Robotics and Soft Actuators)
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26 pages, 3365 KiB  
Review
A Review of Piezoelectric Material-Based Structural Control and Health Monitoring Techniques for Engineering Structures: Challenges and Opportunities
by Abdul Aabid, Bisma Parveez, Md Abdul Raheman, Yasser E. Ibrahim, Asraar Anjum, Meftah Hrairi, Nagma Parveen and Jalal Mohammed Zayan
Actuators 2021, 10(5), 101; https://doi.org/10.3390/act10050101 - 10 May 2021
Cited by 75 | Viewed by 9563
Abstract
With the breadth of applications and analysis performed over the last few decades, it would not be an exaggeration to call piezoelectric materials “the top of the crop” of smart materials. Piezoelectric materials have emerged as the most researched materials for practical applications [...] Read more.
With the breadth of applications and analysis performed over the last few decades, it would not be an exaggeration to call piezoelectric materials “the top of the crop” of smart materials. Piezoelectric materials have emerged as the most researched materials for practical applications among the numerous smart materials. They owe it to a few main reasons, including low cost, high bandwidth of service, availability in a variety of formats, and ease of handling and execution. Several authors have used piezoelectric materials as sensors and actuators to effectively control structural vibrations, noise, and active control, as well as for structural health monitoring, over the last three decades. These studies cover a wide range of engineering disciplines, from vast space systems to aerospace, automotive, civil, and biomedical engineering. Therefore, in this review, a study has been reported on piezoelectric materials and their advantages in engineering fields with fundamental modeling and applications. Next, the new approaches and hypotheses suggested by different scholars are also explored for control/repair methods and the structural health monitoring of engineering structures. Lastly, the challenges and opportunities has been discussed based on the exhaustive literature studies for future work. As a result, this review can serve as a guideline for the researchers who want to use piezoelectric materials for engineering structures. Full article
(This article belongs to the Special Issue Vibration Control and Structure Health Monitoring)
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21 pages, 7895 KiB  
Article
Design, Manufacturing, and Characterization of Thin, Core-Free, Rolled Dielectric Elastomer Actuators
by Julian Kunze, Johannes Prechtl, Daniel Bruch, Bettina Fasolt, Sophie Nalbach, Paul Motzki, Stefan Seelecke and Gianluca Rizzello
Actuators 2021, 10(4), 69; https://doi.org/10.3390/act10040069 - 30 Mar 2021
Cited by 26 | Viewed by 5949
Abstract
In this work, we develop a coreless rolled dielectric elastomer actuator (CORDEA) to be used as artificial muscles in soft robotic structures. The new CORDEA concept is based on a 50 µm silicone film with screen-printed electrodes made of carbon black suspended in [...] Read more.
In this work, we develop a coreless rolled dielectric elastomer actuator (CORDEA) to be used as artificial muscles in soft robotic structures. The new CORDEA concept is based on a 50 µm silicone film with screen-printed electrodes made of carbon black suspended in polydimethylsiloxane. Two printed silicone films are stacked together and then tightly rolled in a spiral-like structure. Readily available off-the-shelf components are used to implement both electrical and mechanical contacts. A novel manufacturing process is developed to enable the production of rolled actuators without a hollow core, with a focus on simplicity and reliability. In this way, actuator systems with high energy density can be effectively achieved. After presenting the design, an experimental evaluation of the CORDEA electromechanical behavior is performed. Finally, actuator experiments in which the CORDEA is pre-loaded with a mass load and subsequently subject to cycling voltage are illustrated, and the resulting performance is discussed. Full article
(This article belongs to the Special Issue Electroactive Polymer Actuators)
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19 pages, 3728 KiB  
Article
Universal Control of Permanent Magnet Synchronous Motors with Uncertain Dynamics
by Rishil Kirankumar Lakhe, Hicham Chaoui, Mohamad Alzayed and Shichao Liu
Actuators 2021, 10(3), 49; https://doi.org/10.3390/act10030049 - 3 Mar 2021
Cited by 14 | Viewed by 5333
Abstract
This paper focuses on the universal control design of permanent magnet synchronous motors (PMSMs) with uncertain system dynamics. In vector control, classical proportional-integral (PI) controllers are used to control d-q axis currents and speed of the PMSM. This paper uses two control methods: [...] Read more.
This paper focuses on the universal control design of permanent magnet synchronous motors (PMSMs) with uncertain system dynamics. In vector control, classical proportional-integral (PI) controllers are used to control d-q axis currents and speed of the PMSM. This paper uses two control methods: conventional field-oriented vector control and simplified control. First, all the control gains are determined for numerous PMSMs with various power ratings using an empirical study and generalized mathematical expressions are derived for each of the gains. Then, these expressions are used for automatic gain calculation for various PMSMs with a wide power-rating range. In vector control, the control gains are determined using only the motor power ratings. In the simplified control, generalized control gain expressions are obtained using the number of pole pairs and the flux linkage. Compared to the vector control, the simplified control method provides much simpler generalized mathematical expressions. Validation is carried out in MATLAB/Simulink environment using various PMSMs from 0.2 HP to 10 HP, and results show accurate tracking of reference speed and d-q axis reference currents. Thus, the proposed gain scheduling approach is effective and can be used for self-commissioning motor drives. Full article
(This article belongs to the Section Actuators for Land Transport)
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11 pages, 2694 KiB  
Article
Piezoelectric MEMS Linear Motor for Nanopositioning Applications
by Víctor Ruiz-Díez, Jorge Hernando-García, Javier Toledo, Abdallah Ababneh, Helmut Seidel and José Luis Sánchez-Rojas
Actuators 2021, 10(2), 36; https://doi.org/10.3390/act10020036 - 18 Feb 2021
Cited by 15 | Viewed by 5473
Abstract
This paper reports the design, fabrication, and performance of piezoelectric bidirectional conveyors based on microelectromechanical systems (MEMS) and featuring 3D-printed legs in bridge resonators. The structures consisted of aluminum-nitride (AlN) piezoelectric film on top of millimeter-sized rectangular thin silicon bridges and two electrode [...] Read more.
This paper reports the design, fabrication, and performance of piezoelectric bidirectional conveyors based on microelectromechanical systems (MEMS) and featuring 3D-printed legs in bridge resonators. The structures consisted of aluminum-nitride (AlN) piezoelectric film on top of millimeter-sized rectangular thin silicon bridges and two electrode patches. The position and size of the patches were analytically optimized for travelling or standing wave generation, while the addition of 3D-printed legs allowed for a controlled contact and amplified displacement, a further step into the manufacturing of efficient linear motors. Such hybrid devices have recently demonstrated the conveyance of sliders of several times the motor weight, with speeds of 1.7 mm/s by travelling waves generated at 6 V and 19.3 kHz. In this paper both travelling and standing wave motors are compared. By the optimization of various aspects of the device such as the vibrational modes, leg collocation and excitation signals, speeds as high as 35 mm/s, and payloads above 10 times the motor weight were demonstrated. The devices exhibited a promising positional resolution while actuated with only a few sinusoidal cycles in an open-loop configuration. Discrete steps as low as 70 nm were measured in the conveyance of 2-mg sliders. Full article
(This article belongs to the Special Issue Selected Papers from the 1st International Electronic Conference on Actuator Technology: Materials, Devices and Applications (IeCAT))
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17 pages, 4812 KiB  
Article
Torque Characteristics Analysis of a Magnetorheological Brake with Double Brake Disc
by Guoliang Hu, Lifan Wu and Linsen Li
Actuators 2021, 10(2), 23; https://doi.org/10.3390/act10020023 - 27 Jan 2021
Cited by 31 | Viewed by 4879
Abstract
Magnetorheological (MR) brake is a sort of electromagnetic brake that uses the controllable output characteristics of MR fluid for braking. In this paper, an MR brake with a double brake disc was developed to improve the braking performance of conventional MR brakes. The [...] Read more.
Magnetorheological (MR) brake is a sort of electromagnetic brake that uses the controllable output characteristics of MR fluid for braking. In this paper, an MR brake with a double brake disc was developed to improve the braking performance of conventional MR brakes. The effective damping gaps were increased from the traditional two sections to four sections by increasing the single brake disc of the conventional MR brake to a double brake disc. By reasonably arranging the non-magnetic sleeve inside the MR brake, the magnetic flux lines were better guided to the effective damping gaps, which increased the utilization rate of the magnetic field, effectively enhanced the braking performance, and also reduced the braking power consumption. The structure and working principle of the MR brake with double brake disc were discussed. The magnetic field of the proposed MR brake was analyzed by ANSYS software, and the theoretical result of braking performance was obtained by combining the established mechanical model. The braking performance test rig was setup to investigate the torque performance of the MR brake. The experimental results show that the maximum braking torque is 18.01 N·m at the applied current of 2.0 A and the rotational speed of 400 r·min−1, and the simulation values are basically verified. In addition, the results indicate that the constant torque characteristic of the MR brake is relatively stable, and the torque is almost unaffected by the changes of rotational speed. The results can provide some guidance for the structural design and optimization of the MR actuators. Full article
(This article belongs to the Section Actuators for Land Transport)
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12 pages, 8895 KiB  
Article
Analysis of the Nonlinear Response of Piezo-Micromirrors with the Harmonic Balance Method
by Andrea Opreni, Nicolò Boni, Roberto Carminati and Attilio Frangi
Actuators 2021, 10(2), 21; https://doi.org/10.3390/act10020021 - 25 Jan 2021
Cited by 30 | Viewed by 5486
Abstract
In this work, we address the simulation and testing of MEMS micromirrors with hardening and softening behaviour excited with patches of piezoelectric materials. The forces exerted by the piezoelectric patches are modelled by means of the theory of ferroelectrics developed by Landau–Devonshire and [...] Read more.
In this work, we address the simulation and testing of MEMS micromirrors with hardening and softening behaviour excited with patches of piezoelectric materials. The forces exerted by the piezoelectric patches are modelled by means of the theory of ferroelectrics developed by Landau–Devonshire and are based on the experimentally measured polarisation hysteresis loops. The large rotations experienced by the mirrors also induce geometrical nonlinearities in the formulation up to cubic order. The solution of the proposed model is performed by discretising the device geometry using the Finite Element Method, and the resulting large system of coupled differential equations is solved by means of the Harmonic Balance Method. Numerical results were validated with experimental data collected on the devices. Full article
(This article belongs to the Special Issue Feature Papers to Celebrate the SCIE Coverage)
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23 pages, 4289 KiB  
Article
Active Disturbance Rejection Control for Position Tracking of Electro-Hydraulic Servo Systems under Modeling Uncertainty and External Load
by Manh Hung Nguyen, Hoang Vu Dao and Kyoung Kwan Ahn
Actuators 2021, 10(2), 20; https://doi.org/10.3390/act10020020 - 22 Jan 2021
Cited by 32 | Viewed by 5368
Abstract
In this paper, an active disturbance rejection control is designed to improve the position tracking performance of an electro-hydraulic actuation system in the presence of parametric uncertainties, non-parametric uncertainties, and external disturbances as well. The disturbance observers (Dos) are proposed to estimate not [...] Read more.
In this paper, an active disturbance rejection control is designed to improve the position tracking performance of an electro-hydraulic actuation system in the presence of parametric uncertainties, non-parametric uncertainties, and external disturbances as well. The disturbance observers (Dos) are proposed to estimate not only the matched lumped uncertainties but also mismatched disturbance. Without the velocity measurement, the unmeasurable angular velocity is robustly calculated based on the high-order Levant’s exact differentiator. These disturbances and angular velocity are integrated into the control design system based on the backstepping framework which guarantees high-accuracy tracking performance. The system stability analysis is analyzed by using the Lyapunov theory. Simulations based on an electro-hydraulic rotary actuator are conducted to verify the effectiveness of the proposed control method. Full article
(This article belongs to the Special Issue Advanced Fluid Power Systems and Actuators)
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10 pages, 2473 KiB  
Article
High-Speed, Helical and Self-Coiled Dielectric Polymer Actuator
by Johannes Mersch, Markus Koenigsdorff, Andreas Nocke, Chokri Cherif and Gerald Gerlach
Actuators 2021, 10(1), 15; https://doi.org/10.3390/act10010015 - 15 Jan 2021
Cited by 11 | Viewed by 4384
Abstract
Novel actuator materials are necessary to advance the field of soft robotics. However, since current solutions are limited in terms of strain, strain rate, or robustness, a new actuator type was developed. In its basic configuration, this actuator consisted of four layers and [...] Read more.
Novel actuator materials are necessary to advance the field of soft robotics. However, since current solutions are limited in terms of strain, strain rate, or robustness, a new actuator type was developed. In its basic configuration, this actuator consisted of four layers and self-coiled into a helix after pre-stretching. The actuator principle was a dielectric polymer actuator. Instead of an elastomer, a thin thermoplastic film, in this case polyethylene, was used as the dielectric and the typically low potential strain was amplified more than 40 times by the helical set-up. In a hot press, the thermoplastic film was joined together with layers of carbon black employed as electrodes and a highly elastic thermoplastic polyurethane film. Once the stack was laser cut into thin strips, they were then stretched over the polyethylene (PE) film’s limit of elasticity and released, thus forming a helix. The manufactured prototype showed a maximum strain of 2% while lifting six times its own weight at actuation frequencies of 3 Hz, which is equivalent to a strain rate of 12%/s. This shows the great potential of the newly developed actuator type. Nevertheless, materials, geometry as well as the manufacturing process are still subject to optimization. Full article
(This article belongs to the Special Issue Polymeric Actuators 2020)
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17 pages, 25523 KiB  
Article
Design of a 2DoF Ankle Exoskeleton with a Polycentric Structure and a Bi-Directional Tendon-Driven Actuator Controlled Using a PID Neural Network
by Taehoon Lee, Inwoo Kim and Yoon Su Baek
Actuators 2021, 10(1), 9; https://doi.org/10.3390/act10010009 - 4 Jan 2021
Cited by 21 | Viewed by 6006
Abstract
Lower limb exoskeleton robots help with walking movements through mechanical force, by identifying the wearer’s walking intention. When the exoskeleton robot is lightweight and comfortable to wear, the stability of walking increases, and energy can be used efficiently. However, because it is difficult [...] Read more.
Lower limb exoskeleton robots help with walking movements through mechanical force, by identifying the wearer’s walking intention. When the exoskeleton robot is lightweight and comfortable to wear, the stability of walking increases, and energy can be used efficiently. However, because it is difficult to implement the complex anatomical movements of the human body, most are designed simply. Due to this, misalignment between the human and robot movement causes the wearer to feel uncomfortable, and the stability of walking is reduced. In this paper, we developed a two degrees of freedom (2DoF) ankle exoskeleton robot with a subtalar joint and a talocrural joint, applying a four-bar linkage to realize the anatomical movement of a simple 1DoF structure mainly used for ankles. However, bidirectional tendon-driven actuators (BTDAs) do not consider the difference in a length change of both cables due to dorsiflexion (DF) and plantar flexion (PF) during walking, causing misalignment. To solve this problem, a BTDA was developed by considering the length change of both cables. Cable-driven actuators and exoskeleton robot systems create uncertainty. Accordingly, adaptive control was performed with a proportional-integral-differential neural network (PIDNN) controller to minimize system uncertainty. Full article
(This article belongs to the Special Issue Actuators on Soft Exoskeletons)
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17 pages, 7104 KiB  
Article
Self-Healing and High Interfacial Strength in Multi-Material Soft Pneumatic Robots via Reversible Diels–Alder Bonds
by Seppe Terryn, Ellen Roels, Joost Brancart, Guy Van Assche and Bram Vanderborght
Actuators 2020, 9(2), 34; https://doi.org/10.3390/act9020034 - 30 Apr 2020
Cited by 45 | Viewed by 8679
Abstract
In new-generation soft robots, the actuation performance can be increased by using multiple materials in the actuator designs. However, the lifetime of these actuators is often limited due to failure that occurs at the weak multi-material interfaces that rely almost entirely on physical [...] Read more.
In new-generation soft robots, the actuation performance can be increased by using multiple materials in the actuator designs. However, the lifetime of these actuators is often limited due to failure that occurs at the weak multi-material interfaces that rely almost entirely on physical interactions and where stress concentration appears during actuation. This paper proposes to develop soft pneumatic actuators out of multiple Diels–Alder polymers that can generate strong covalent bonds at the multi-material interface by means of a heat–cool cycle. Through tensile testing it is proven that high interfacial strength can be obtained between two merged Diels–Alder polymers. This merging principle is exploited in the manufacturing of multi-material bending soft pneumatic actuators in which interfaces are no longer the weakest links. The applicability of the actuators is illustrated by their operation in a soft hand and a soft gripper demonstrator. In addition, the use of Diels–Alder polymers incorporates healability in bending actuators. It is experimentally illustrated that full recovery of severe damage can be obtained by subjecting the multi-material actuators to a healing cycle. Full article
(This article belongs to the Special Issue Pneumatic Soft Actuators)
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30 pages, 4306 KiB  
Review
Review of Modeling and Control of Magnetostrictive Actuators
by Valerio Apicella, Carmine Stefano Clemente, Daniele Davino, Damiano Leone and Ciro Visone
Actuators 2019, 8(2), 45; https://doi.org/10.3390/act8020045 - 29 May 2019
Cited by 86 | Viewed by 16499
Abstract
Magnetostrictive actuators play an important role in the perception of usefulness of smart materials and devices. Their applications are potentially wider than that of piezoelectric actuators because of the higher energy density and intrinsic robustness. However, the non-negligible hysteresis and complexity of their [...] Read more.
Magnetostrictive actuators play an important role in the perception of usefulness of smart materials and devices. Their applications are potentially wider than that of piezoelectric actuators because of the higher energy density and intrinsic robustness. However, the non-negligible hysteresis and complexity of their characteristics make the design and control quite difficult and has limited their diffusion in industrial applications. Nevertheless, the scientific literature presents a wide offer of results in design and geometries, modeling and control that may be exploited for applications. This paper gives a reasoned review of the main results achieved in the literature about design, modeling and control of magnetostrictive actuators exploiting the direct effects of magnetostriction (Joule and Wiedemann). Some perspectives and challenges about magnetostrictive actuators development are also gathered. Full article
(This article belongs to the Special Issue Smart Materials-Based Actuators)
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28 pages, 11227 KiB  
Article
Conductive Fabric Heaters for Heat-Activated Soft Actuators
by Mark Cartolano, Boxi Xia, Aslan Miriyev and Hod Lipson
Actuators 2019, 8(1), 9; https://doi.org/10.3390/act8010009 - 21 Jan 2019
Cited by 28 | Viewed by 14327
Abstract
We examine electrically conductive fabrics as conductive heaters for heat-activated soft actuators. We have explored various fabric designs optimized for material properties, heat distribution and actuation/de-actuation characteristics of the soft actuators. We implemented this approach in the silicone/ethanol composite actuators, in which ethanol [...] Read more.
We examine electrically conductive fabrics as conductive heaters for heat-activated soft actuators. We have explored various fabric designs optimized for material properties, heat distribution and actuation/de-actuation characteristics of the soft actuators. We implemented this approach in the silicone/ethanol composite actuators, in which ethanol undergoes a thermally-induced phase change, leading to high actuation stress and strain. Various types of conductive fabrics were tested, and we developed a stretchable kirigami-based fabric design. We demonstrate a fabric heater that is capable of cyclic heating of the actuator to the required 80 °C. The fabric with the special kirigami design can withstand temperatures of up to 195 °C, can consume up to 30 W of power, and allows the actuator to reach >30% linear strain. This technology may be used in various systems involving thermally-induced actuation. Full article
(This article belongs to the Special Issue New Materials and Designs for Soft Actuators)
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