Types Of Actuators Research Articles

Computational Analysis of Semi-Analytical Modeling Techniques for a Novel PM-Based Planar Actuator

A novel type of permanent magnet planar actuator is proposed which consists of a permanent magnet mover that interacts with individually mechanically controllable permanent magnets in the stator. A state of levitation and actuation is obtained by mechanically altering the orientation of the stator magnets to control the forces and torques on the mover. To design and control the actuator, fast and accurate electromagnetic models are required. In this study, the harmonic modeling technique is applied to rotating and translating cuboidal and cylindrical permanent magnets and is compared to the equivalent charge model in terms of accuracy and computational effort. The models are compared for a finite stator topology which demonstrates that the harmonic model has a substantial computational advantage over the equivalent charge method in a non-periodic system while both models are in good agreement in terms of accuracy.

Reconfiguration control allocation of actuator faults for tailless aircraft with low aspect ratio

The triaxial attitude control of the tailless aircraft depends heavily on the effectiveness of the actuators. Still, the actuators have redundancy characteristics, cross-coupling of rudder effect, and so on. Therefore, the reconfigurable control allocation of the tailless aircraft under typical actuator faults is deeply studied in this paper. The effectiveness and rationality of the incremental control allocation method based on quadratic programming are thoroughly verified for application to maximize the residual control ability of the aircraft, ensure that the aircraft can still complete the flight mission typically, and guarantee flight safety. According to the research principle of surface failures from slight to severe, three typical rudder surface faults are designed successively: Efficiency loss of single actuator, single actuator stuckness, and double actuators combined stuckness. On this basis, the mechanism of reconfiguration allocation after actuator failures is studied, and the residual control ability of the actuator after loss is fully explored. What’s more, the range of allowable reduction of efficiency of each actuator and the acceptable stuck angle range of each actuator are explored, and the most severe failure in the combination of double actuators stuck is obtained. The attitude controller is designed with incremental backstepping (IBKS). The reconstruction allocation adopts a quadratic programming allocation method based on an effective set solver, which can be seamlessly connected with the IBKS method to improve the control accuracy and disturbance immunity effectively.

SoJel –A 3D printed jellyfish-like robot using soft materials for underwater applications

Mass manufactured, biologically inspired soft robots are needed for safe robot-animal interactions. The key challenges are the design and manufacture of high-performance robots that meet stringent requirements in ocean environments. This work describes a 92% 3D-printed jellyfish-inspired soft robot, SoJel, which uses soft polymers for the bell and sensors. We show how slight variations in geometry affects the swimming performance of the robot, which demonstrates the need for advanced or custom-made 3D printers that avoid the difficulties in realizing controlled geometries by using traditional molding and casting techniques. The design reproduces important kinematic patterns of natural jellyfish, like the bell bending angle, actuation duty cycle, and bell kinematics. This work builds on previous generations of jellyfish-inspired robots that employed various types of actuators, but is largely polymer based, so it avoids metallic components that are susceptible to corrosion in the ocean. The realized cost of transport and vertical swimming height of robots powered by coiled nickel-titanium actuators are comparable to previous designs, however, the present robots have advantages in ease of design and manufacturing. A variety of soft robots and flexible structures can potentially be fabricated using this design principle. Flexible 3D-printed soft sensors enable us to determine the bending angles for motion estimation and control. Energy harvesting from water oscillation or free vibration is demonstrated using a twistron harvester and a piezoelectric composite integrated into the robot, which can be used for powering electronics, such as a LED for display and communication.

Characteristic Analysis of Heterochiral TCP Muscle as a Extensile Actuator for Soft Robotics Applications

A soft actuator is an essential component in a soft robot that enables it to perform complex movements by combining different fundamental motion modes. One type of soft actuator that has received significant attention is the twisted and coiled polymer artificial muscle (TCP actuator). Despite many recent advancements in TCP actuator research, its use as an extensile actuator is less common in the literature. This works introduces the concept of using TCP actuators as thermal-driven extensile actuators for robotics applications. The low-profile actuator can be easily fabricated to offer two unique deformation capabilities. Results from the characterization indicate that extensile actuators, made with various rod diameters and under different load conditions, display remarkable elongation deformation. Additionally, a proof-of-concept soft-earthworm robot was developed to showcase the potential application of the extensile actuator and to demonstrate the benefits of combining different types of motion modes.

Bioinspired soft robots based on organic polymer-crystal hybrid materials with response to temperature and humidity

The capability of stimulated response by mechanical deformation to induce motion or actuation is the foundation of lightweight organic, dynamic materials for designing light and soft robots. Various biomimetic soft robots are constructed to demonstrate the vast versatility of responses and flexibility in shape-shifting. We now report that the integration of organic molecular crystals and polymers brings about synergistic improvement in the performance of both materials as a hybrid materials class, with the polymers adding hygroresponsive and thermally responsive functionalities to the crystals. The resulting hybrid dynamic elements respond within milliseconds, which represents several orders of magnitude of improvement in the time response relative to some other type of common actuators. Combining molecular crystals with polymers brings crystals as largely overlooked materials much closer to specific applications in soft (micro)robotics and related fields.

Soft and lightweight fabric enables powerful and high-range pneumatic actuation.

Soft structures and actuation allow robots, conventionally consisting of rigid components, to perform more compliant, adaptive interactions similar to living creatures. Although numerous functions of these types of actuators have been demonstrated in the literature, their hyperelastic designs generally suffer from limited workspaces and load-carrying capabilities primarily due to their structural stretchability factor. Here, we describe a series of pneumatic actuators based on soft but less stretchable fabric that can simultaneously perform tunable workspace and bear a high payload. The motion mode of the actuator is programmable, combinable, and predictable and is informed by rapid response to low input pressure. A robotic gripper using three fabric actuators is also presented. The gripper demonstrates a grasping force of over 150 N and a grasping range from 70 to 350millimeters. The design concept and comprehensive guidelines presented would provide design and analysis foundations for applying less stretchable yet soft materials in soft robots to further enhance their practicality.

State of the Art in Wearable Wrist Exoskeletons Part I: Background Needs and Design Requirements

Despite an increase in the use of exoskeletons, particularly for medical and occupational applications, few studies have focused on the wrist, even though it is the fourth most common site of musculoskeletal pain in the upper limb. The first part of this paper will present the key challenges to be addressed to implement wrist exoskeletons as wearable devices for novel rehabilitation practices and tools in the occupational/industrial sector. Since the wrist is one of the most complex joints in the body, an understanding of the bio-mechanics and musculo-skeletal disorders of the wrist is essential to extracting design requirements. Depending on the application, each wrist exoskeleton has certain specific design requirements. These requirements have been categorized into six sections: purpose, kinematics, dynamics, rigidity, ergonomics, and safety. These form the driving factors behind the choice of a design depending on the objectives. Different design architectures are explored, forming the basis for the various technical challenges that relate to: actuation type, power source, power transmission, sensing, and control architecture. This paper summarizes, in a systematic approach, all the current technologies adopted, analyzes their benefits and limitations, and finally proposes future perspectives.

Active fault-tolerant control scheme for four-wheel independent drive electric vehicles under actuator faults

For chassis-by-wire in four-wheel independent drive electric vehicles (4WID-EVs), a large number of controllable actuators with control systems and electrical systems make the vehicle more sensitive to the failure of electronic components in actuators. When actuator faults occur, the stability and handling performance of 4WID-EVs will deteriorate, even affecting the driving safety. To handle this problem, the typical actuator faults of 4WID-EVs and their characteristics are firstly analyzed in detail. After that, a control-oriented uncertain 7 degrees of freedom vehicle dynamics model is established. Then, a modified sliding mode active fault tolerant control (FTC) scheme with layered architecture is proposed, which contains the upper and lower layers. In the upper layer, a modified sliding mode controller with a nonlinear extended state observer is designed to track the reference states under the influence of model uncertainty. In the lower layer, an improved torque distribution algorithm is proposed to compensate for the limited direct yaw moment caused by in-wheel motor faults. Comparison works are carried out both in simulation and experiment. Simulation results show that the proposed method improves performance by 80.5% and 70.2% compared with existing FTC method under 2 fault conditions, respectively. Furthermore, real vehicle experiments also indicate that the proposed method improves performance by 59.6% and 74.4% under two pre-set fault conditions, respectively. The proposed method might provide a theoretical reference for actual controller design in 4WID-EVs.

Structural Design and Analysis of New Electromagnetic Actuator

active vibration control can effectively restrain low-frequency line spectrum vibration. As an output end of control force, an electromagnetic actuator has the problem of low precision of output force and zero drift. Therefore, a new type of electromagnetic actuator is designed in this paper. The parametric modeling of the magnetic circuit structure is carried out, and it is verified that the magnetostatic attraction in direct current (DC) magnetic circuit is zero. Then, a calculation method of electromagnetic force in alternating current/direct current (AC/DC) magnetic circuit is deduced. The mechanical-electrical-magnetic-thermal multi-physical coupling field simulation of the electromagnetic actuator is carried out, which shows that the improved magnetic circuit structure effectively solves the zero drift, improves the precision of output force of the actuator, and allows the actuator to have lower electromagnetic heat output and electromagnetic loss.

Analysis of a Soft Bio-Inspired Active Actuation Model for the Design of Artificial Vocal Folds

AbstractPhonation results from the passively induced oscillation of the vocal folds in the larynx, creating sound waves that are then articulated by the mouth and nose. Patients undergoing laryngectomy have their vocal folds removed and thus must rely on alternative sources of achieving the desired vibration of artificial vocal folds. Existing solutions, such as voice prostheses and the Electrolarynx, are limited by producing sufficient voice quality, for instance. In this paper, we present a mathematical analysis of a physical model of an active vocal fold prosthesis. The inverse dynamical equation of the system will help to understand whether specific types of soft actuators can produce the required force to generate natural phonations. Hence, this is referred to as the active actuation model. We present the analysis to replicate the vowels /a/, /e/, /i/, and /u/ and voice qualities of vocal fry, modal, falsetto, breathy, pressed, and whispery. These characteristics would be required as a first step to design an artificial vocal folds system. Inverse dynamics is used to identify the required forces to change the glottis area and frequencies to achieve sufficient oscillation of artificial vocal folds. Two types of ionic polymer-metal composite (IPMC) actuators are used to assess their ability to produce these forces and the corresponding activation voltages required. The results of our proposed analysis will enable research into the effects of natural phonation and, further, provide the foundational work for the creation of advanced larynx prostheses.

Cellular and Molecular Processes Are Differently Influenced in Primary Neural Cells by Slight Changes in the Physicochemical Properties of Multicore Magnetic Nanoparticles

Herein, we use two exemplary superparamagnetic iron oxide multicore nanoparticles (SPIONs) to illustrate the significant influence of slightly different physicochemical properties on the cellular and molecular processes that define SPION interplay with primary neural cells. Particularly, we have designed two different SPION structures, NFA (i.e., a denser multicore structure accompanied by a slightly less negative surface charge and a higher magnetic response) and NFD (i.e., a larger surface area and more negatively charged), and identified specific biological responses dependent on SPION type, concentration, exposure time, and magnetic actuation. Interestingly, NFA SPIONs display a higher cell uptake, likely driven by their less negative surface and smaller protein corona, more significantly impacting cell viability and complexity. The tight contact of both SPIONs with neural cell membranes results in the significant augmentation of phosphatidylcholine, phosphatidylserine, and sphingomyelin and the reduction of free fatty acids and triacylglycerides for both SPIONs. Nonetheless, NFD induces greater effects on lipids, especially under magnetic actuation, likely indicating a preferential membranal location and/or a tighter interaction with membrane lipids than NFA, in agreement with their lower cell uptake. From a functional perspective, these lipid changes correlate with an increase in plasma membrane fluidity, again larger for more negatively charged nanoparticles (NFD). Finally, the mRNA expression of iron-related genes such as Ireb-2 and Fth-1 remains unaltered, while TfR-1 is only detected in SPION-treated cells. Taken together, these results demonstrate the substantial impact that minor physicochemical differences of nanomaterials may exert in the specific targeting of cellular and molecular processes. A denser multicore structure generated by autoclave-based production is accompanied by a slight difference in surface charge and magnetic properties that become decisive for the biological impact of these SPIONs. Their capacity to markedly modify the lipidic cell content makes them attractive as lipid-targetable nanomedicines.

Adaptive Magnetoactive Soft Composites for Modular and Reconfigurable Actuators

AbstractMagnetoactive soft materials, typically composed of magnetic particles dispersed in a soft polymer matrix, are finding many applications in soft robotics due to their reversible and remote shape transformations under magnetic fields. To achieve complex shape transformations, anisotropic, and heterogeneous magnetization profiles must be programmed in the material. However, once programmed and assembled, magnetic soft actuators cannot be easily reconfigured, repurposed, or repaired, which limits their application, their durability, and versatility in their design. Here, magnetoactive soft composites are developed from squid‐derived biopolymers and NdFeB microparticles with tunable ferromagnetic and thermomechanical properties. By leveraging reversible crosslinking nanostructures in the biopolymer matrix, a healing‐assisted assembly process is developed that allows for on‐demand reconfiguration and magnetic reprogramming of magnetoactive composites. This concept in multi‐material modular actuators is demonstrated with programmable deformation modes, self‐healing properties to recover their function after mechanical damage, and shape‐memory behavior to lock in their preferred configuration and un‐actuated catch states. These dynamic magnetic soft composites can enable the modular design and assembly of new types of magnetic actuators, not only eliminating device vulnerabilities through healing and repair but also by providing adaptive mechanisms to reconfigure their function on demand.

Modular Soft Robot with Origami Skin for Versatile Applications.

Recent advances in soft robotics demonstrate the requirement of modular actuation to enable the rapid replacement of actuators for maintenance and functionality extension. There remain challenges to designing soft actuators capable of different motions with a consistent appearance for simplifying fabrication and modular connection. Origami structures reshaping along with their unique creases became a powerful tool to provide compact constraint layers for soft pneumatic actuators. Inspired by Waterbomb and Kresling origami, this article presents three types of vacuum-driven soft actuators with a cubic shape and different origami skins, featuring contraction, bending, and twisting-contraction combined motions, respectively. In addition, these modular actuators with diversified motion patterns can be directly fabricated by molding silicone shell and constraint layers together. Actuators with different geometrical parameters are characterized to optimize the structure and maximize output properties after establishing a theoretical model to predict the deformation. Owing to the shape consistency, our actuators can be further modularized to achieve modular actuation via mortise and tenon-based structures, promoting the possibility and efficiency of module connection for versatile tasks. Eventually, several types of modular soft robots are created to achieve fragile object manipulation and locomotion in various environments to show their potential applications.

A Review of Actuators in Ankle-Foot Rehabilitation Therapy

Ankle injury is one of the physical injuries that commonly occur during physical related activities, especially in sports. Currently, there are established treatments for ankle rehabilitation at the hospital. This treatment involves range of motion exercises and endurance exercises. However, current treatment requires patients to visit to hospital frequently which is very repetitive in nature. Ankle rehabilitation robots are developed to enhance ankle strength, flexibility and proprioception after injury and promote motor learning and ankle plasticity in patients with drop foot. This article reviews the types of actuators used in ankle rehabilitation and discusses the evolution of industrial robotics towards rehabilitation.

“Water to the ropes”: A predictive model for the supercontraction stress of spider silks

When humidified at different moisture conditions, restrained spider silk fibers can exhibit a very high supercontraction phenomenon. The hydration water molecules induce a Hydrogen-bonds disruption process that, due to entropic effects, decreases the natural – zero force – end-to-end chains length. By considering a bundle of macromolecules, we describe supercontraction as a possible actuation system and determine the maximum actuation force depending on the silk properties at the molecular scale and on the constraining system representing other silk threads or the actuated device. The comparison with experimental results of Argiope trifasciata silk fibers show the effectiveness of the proposed model in quantitatively predicting the experimental actuation properties. The considered historical case study of obelisk rescue in Saint Peter’s Square (Rome) through ropes hydration is discussed evidencing the optimal performances of this natural material adopted as moisture powered actuator: we obtain a work density of 2.19 kJ/m3 making spider silk the most performant hydration driven active material. Moreover we obtain a power density of the order of 730 W/kg about three times the most performant carbon nanotube actuators making such material very competitive as compared with all types of actuators. The analytic description of the macroscopic actuation parameters from microscale properties shows the possibility of adopting our approach also in the field of bioinspired artificial silks design, possibly considering also important non-linear effects in the actuated system.

Skin‐Mountable Vibrotactile Stimulator Based on Laterally Multilayered Dielectric Elastomer Actuators

AbstractSkin‐stimulation technology has attracted intense attention for virtual/augmented reality applications and tactile‐feedback systems. However, bulky, heavy, and stiff characteristics of existing skin‐stimulating devices limit their wearability and comfort, thus disturbing the immersive experience of users. This study presents a new type of thin and lightweight dielectric elastomer actuator for developing a skin‐mountable vibrotactile stimulator. A new methodology is suggested to enhance the operating efficiency of dielectric elastomer actuators based on a laterally aligned dielectric multilayer structure (≈900 layer) with short dielectric distance (≈10 µm) and a soft elastomer/ionic liquid composite with low modulus and high dielectric constant. With the improved structural/material properties, the flexible actuator exhibits high displacements at low operating voltage (<200 V) over a wide frequency range (≈800 Hz). Therefore, the finger‐band type vibrotactile stimulator based on the laterally multilayered dielectric elastomer actuators can exert indentations that have the ability of stimulating all mechanoreceptors in human skin over the full perception frequency/amplitude range. In addition, the actuator shows a high electromechanical stability for long‐term operation due to time‐efficient and precise fabrication process using sophisticated photolithography and secondary sputtering. Therefore, this vibrotactile stimulator shows high promise for use in tactile‐assistive devices, tactile communications, haptic feedback, and beyond.

Actuation response of typical biased shape memory alloy wire under variable electric heating rates: Experimental investigation and modeling

Electric heating is commonly used to induce the inverse martensitic transformation in shape memory alloy (SMA) wire actuators. Different actuation responses can be achieved when adjusting the heating currents. In this study, typical biased NiTi SMA wire actuators were tested under the heating currents of 1.5 A, 3 A, 4 A, and 5 A. It was found that SMA wire actuators under three typical biases (dead weight, linear spring, dead weight & linear spring) behaved differently as the heating current increased. Moreover, under dead weight bias and mixed bias, high heating currents tended to cause dynamic responses during actuation. The maximum inertia load induced by dynamic responses was 2.65 times as much as the static load. In contrast, the actuation response under linear spring bias was relatively steady. A model based on the SMA constitutive equation and the dynamic equation was also established, which was capable of simulating the dynamic actuation responses of SMA wire actuators under high electric heating rates.

Modeling of bonding piezoelectric stack using conductive adhesive with metal-coated polymer fillers

Bonding piezoelectric stack (BPS) is a common type of piezoelectric stack actuator (PSA) with an adhesive bonding layer. The regular bonding layer in BPS is produced by the dielectric materials, which may lead to electric energy dissipation and thus decrease the displacement of BPS. The dissipation can be compensated by substituting the regular bonding with the conductive adhesive (CA) using the conductive fillers, say, the metal-coated polymer fillers. In order to verify the feasibility of using this new BPS for piezoelectric devices and model-based controller designs, this paper establishes a novel BPS model using CA with metal-coated polymer fillers. In this paper, a dielectric model and a Kelvin–Voigt model are used to describe BPS’s electric and mechanical behaviors using regular bonding. A brief particle-bonding model is used to switch the BPS model using the regular bonding to the model using CA with metal-coated polymer fillers. The theoretical simulation and the experiment results demonstrate that the model has more than 97% accuracy. The results indicate that the dynamic model can accurately predict the displacement of BPS when the CA is used in conjunction with metal-coated polymer fillers and other metal-coated fillers, which can be used to design large-scale piezoelectric devices.

A New Type of Electric Servo Actuator with an Energy Recovery Link and Its Dynamic and Energy Consumption Characteristics Analysis

A New Type of Electric Servo Actuator with an Energy Recovery Link and Its Dynamic and Energy Consumption Characteristics Analysis

Fiber-reinforced liquid crystalline elastomer composite actuators with multi-stimulus response properties and multi-directional morphing capabilities

Liquid crystalline elastomers (LCEs) are promising materials for soft actuations. LCE composites (LCECs), via the inclusion of fillers into LCEs, bring diverse functionalities and stimuli-responsive capabilities. It is still a challenge to improve the mechanical properties of LCEC and ensure that the material can perform reversible transformations. Here we present a cost-effective LCEC design and fabrication method by dispersing continuous carbon fibers and carbon nanotubes into LCEs, forming a new type of LCEC actuator. We found that through adjusting the angle (such as 45° and 90°) between the carbon fiber and the stretching axis of LCEC matrix, complex deformable geometries can be easily achieved including bending and twisting structures with enhanced storage modulus (400.9 MPa at 25 °C). Furthermore, the LCEC actuators could be driven by various stimuli including heat (120 °C), light (800 mW cm−2), and electricity (2.0 V). As a result, our new LCEC actuator outperforms other LCE actuators by having the largest number of morphing geometries and stimulus-responsive modes. Our LCEC design and manufacturing strategy represents a promising general methodology that can be easily extended to other continuous fibers (such as glass fiber, aramid fiber, etc.) filled LCECs, bringing even rich shape-changing capabilities that are needed for soft robots and beyond.