Bidirectional Actuator Research Articles

Design and Applications of High Force Generation in 3D-Printed Pneumatic Artificial Muscles

Increasing the force generation and scalability of soft pneumatic actuators poses significant challenges in robotics applications, especially where high load capacities and precise control are required. This paper presents UniBPAM, a novel, scalable soft pneumatic actuator optimized through 3D printing to enhance force generation. By analyzing design parameters, such as the number of sides, height, and origami factor, UniBPAM achieved a 21.48% increase in force generation. Scalable across diameters from 36 to 144 mm, the actuator demonstrated the ability to lift up to 57 kg with 84.9% strain at larger scales. Additionally, the BiBPAM variant enables bidirectional actuation in robotic joints via motion control, which is realized through PID systems, making it suitable for various robotic applications.

Superhydrophobic asymmetric pH-responsive soft actuators: Implications for the development of anti-fouling medical devices

Biomedical engineering strives for innovation to enhance the safety and effectiveness of medical tools, such as catheters and stents that need to be operated in confined spaces, with precise drug delivery control and should possess anti-fouling properties. Soft actuators with superhydrophobic surfaces can provide adaptable shape change together with non-fouling attributes required for medical devices. In this study, we have developed a Janus film with a hydrophilic solvent-responsive bottom and superhydrophobic top surface using a self-assembly strategy. The devised new strategy involves the dispersal of modified silica nanoparticles into a homogeneous solution, where they were segregated from the polymer matrix and self-assembled to form a superhydrophobic layer on the surface with a water contact angle of >150°. The resulting asymmetric actuator demonstrated bidirectional actuation in solvents with extreme pH values i.e., pH 1 and 13. It could be tailored for specific hydrophilicity by adjusting the ratio of dispersed superhydrophobic and hydrophilic silica nanoparticles in the polymer solution. These films exhibited exceptional chemical stability against strong acids, alkaline solutions, ethanol, and salt, as well as mechanical stability against abrasion from sandpaper. In vitro studies confirmed their superior anti-fouling and anti-bacterial properties. Furthermore, actuation of printed 3D structures with different patterns was demonstrated, showcasing the possibility of developing these superhydrophobic asymmetric surfaces via 3D printing and their potential as cardiovascular stents.

Design and application of bidirectional soft actuator with multiangle chambers

Purpose This study aims to introduce a novel bidirectional soft actuator as an enhancement to conventional pneumatic network actuators. This improvement involves integrating air chambers positioned at specific angles to improve stability, adaptability and grasping efficiency in various environments. Design/methodology/approach The design approach incorporates air chambers positioned at a 45° angle relative to the horizontal direction at the actuator's terminus, along with additional chambers at a 90° angle. Mathematical models are developed for longitudinal and transverse bending, as well as for obliquely connected cavities, based on the assumption of piecewise constant curvature. Analyses are conducted on output forces, bending characteristics and end contact areas for both transverse and longitudinal ends. Findings The proposed soft actuator surpasses traditional pneumatic network actuators in gripping area due to the inclusion of a diagonal air cavity and a transverse pneumatic network structure at the terminus. As a result, it provides torsion and gripping force in both directions. Testing on a dedicated platform with two variants of grippers demonstrates superior gripping force capability and performance in complex environments. Practical implications Through the design of multiangle chambers, the soft actuator exhibits diverse driving angles and morphological variations, offering innovative design perspectives for industrial grasping. Social implications The design of multiangle chambers facilitates personalized configurations of soft actuators by researchers, enabling tailored angles for specific interaction environments to achieve desired functionalities. This approach offers novel insights into soft actuator design, addressing more prevalent industrial grasping challenges. Originality/value This study introduces a novel soft actuator design that significantly enhances gripping capabilities in comparison to conventional pneumatic network actuators. The incorporation of specific air chamber configurations and mathematical modeling provides valuable insights for the development of adaptable and efficient robotic grippers for industrial and household applications.

The driving characteristics of bidirectional SMA wire actuators - Theoretical modeling and experimental testing

Bidirectional shape memory alloy (SMA) wire actuators play a critical role in driving applications thanks to their characteristics in memory shaping and good overall performance. SMA wire actuators were often studied at a single load type, and there is no comprehensive comparison investigation of different SMA wire actuators in the literature. In this paper, the driving characteristics of four available types of SMA wire actuators, namely, dead-load, biased spring, differential type, and biased superelastic SMA wire actuators are modelled mathematically and then tested in laboratory settings. The characteristics of SMA wire actuators are quantitatively measured and then compared under a range of application scenarios. The output displacement and thermal-electric models of NiTi SMA wires are derived based on the Brinson constitutive model with stress effects in consideration. A customized SMA wire actuator test device is developed to evaluate the theocratical models and benchmark testing four types of SMA wires and their driving characteristics, including structure, design, displacement, response and recovery time, energy efficiency and hysteresis properties. The SMA wire phase transformation characteristics of the four actuators are tested under different activation currents, and then quantitatively compared. In conclusion, this paper adds theoretical and experimental significance to the literature on SMA wire actuators. The reference value on the phase transformation characteristics of SMA wires can be used to guide SMA application in industrial designs and enable theoretical studies in complementary research areas.

Super-Flexible Water-Proof Actuators.

Humidity-responsive materials hold broad application prospects in sensing, energy production, and other fields. Particularly, humidity-sensitive, flexibility, and water resistance are pivotal factors in the development of optimized humidity-responsive materials. In this study, hydrophobic linear polyurethane and hydrophilic 4-vinylphenylboronic acid (4-VPBA) form a semi-intercross cross-linking network. This copolymer of polyurethane exhibits excellent humidity-sensitive, mechanical properties, and water resistance. Its maximum tensile strength and maximum elongation can reach 40.56MPa and 543.47%, respectively. After being immersed in water at various temperatures for 15 days, it exhibited a swelling ratio of only 3.28% in water at 5°C and 9.58% in water at 70°C. While the presence of 4-VPBA network imparts humidity-sensitive, reversible, and multidirectional bending abilities, under the stimulus of water vapor, it can bend 43° within 1.4s. The demonstrated material surpasses current bidirectional humidity actuators in actuating ability. Based on these characteristics, automatically opening waterproof umbrellas and windows, as well as bionic-arms, crawling robots, and self-propelled boats, are successfully developed.

Shape‐Memory Alloy‐Based Auxetic Smart Metamaterials: Enabling Inherently Bidirectional Actuation

Auxetic metamaterials, characterized by their negative Poisson's ratio, have garnered significant interest in various fields due to their unique mechanical properties. This article presents a pioneering approach to the development of auxetic smart metamaterials using shape memory alloy (SMA) as the core material. As SMAs can be Joule heated to change between their low‐ and high‐temperature phases to trigger the actuation of the structure, the auxetic smart metamaterial can actively modify its shape and stiffness to produce bidirectional actuation with a single power input and using a single bias mechanical element. The proposed active auxetic metamaterial consists of an SMA plate patterned with auxetic cuts, creating hinges that modulate the deformation of the structure to produce an auxetic behavior. This work looks at the impact of different geometric parameters on the behavior of the structure, including its generated force, its maximum strain, and its Poisson's ratio. The study also investigates the effect of the number of segmented units, revealing that designs with more segmented units suffer from stress concentrations near attachment points, limiting their advantages. This article shows that smart materials can help imbue metamaterials such as auxetic metamaterials with active properties to facilitate their implementation in future robotic applications.

Bidirectional Neuronal Actuation by Uncaging with Violet and Green Light

AbstractWe have developed a photochemical protecting group that enables wavelength selective uncaging using green versus violet light. Change of the exocyclic oxygen of the laser dye coumarin‐102 to sulfur, gave thio‐coumarin‐102, a new chromophore with an absorption ratio at 503/402 nm of 37. Photolysis of thio‐coumarin‐102 caged γ‐aminobutyric acid was found to be highly wavelength selective on neurons, with normalized electrical responses >100‐fold higher in the green versus violet channel. When partnered with coumarin‐102 caged glutamate, we could use whole cell violet and green irradiation to fire and block neuronal action potentials with complete orthogonality. Localized irradiation of different dendritic segments, each connected to a neuronal cell body, in concert with 3‐dimenional Ca2+ imaging, revealed that such inputs could function independently. Chemical signaling in living cells always involves a complex balance of multiple pathways, use of (thio)‐coumarin‐102 caged compounds will enable arbitrarily timed flashes of green and violet light to interrogate two independent pathways simultaneously.

Bidirectional Neuronal Actuation by Uncaging with Violet and Green Light.

We have developed a photochemical protecting group that enables wavelength selective uncaging using green versus violet light. Change of the exocyclic oxygen of the laser dye coumarin-102 to sulfur, gave thio-coumarin-102, a new chromophore with an absorption ratio at 503/402 nm of 37. Photolysis of thio-coumarin-102 caged γ-aminobutyric acid was found to be highly wavelength selective on neurons, with normalized electrical responses >100-fold higher in the green versus violet channel. When partnered with coumarin-102 caged glutamate, we could use whole cell violet and green irradiation to fire and block neuronal action potentials with complete orthogonality. Localized irradiation of different dendritic segments, each connected to a neuronal cell body, in concert with 3-dimenional Ca2+ imaging, revealed that such inputs could function independently. Chemical signaling in living cells always involves a complex balance of multiple pathways, use of (thio)-coumarin-102 caged compounds will enable arbitrarily timed flashes of green and violet light to interrogate two independent pathways simultaneously.

Bioinspired Bidirectional Stiffening Soft Actuators Enable Versatile and Robust Grasping.

The bending stiffness modulation mechanism for soft grippers has gained considerable attention to improve grasping versatility, capacity, and stability. However, lateral stability is usually ignored or hard to achieve at the same time with good bending stiffness modulation performance. Therefore, this article presents a bioinspired bidirectional stiffening soft actuator (BISA), enabling compliant and stable performance. BISA combines the air tendon actuation (ATA) and a bone-like structure (BLS). The ATA is the main actuation of the BISA, and the bending stiffness can be modulated with a maximum stiffness of about 0.7 N/mm and a maximum magnification of three times when the bending angle is 45°. Inspired by the morphological structure of the phalanx, the lateral stiffness can be modulated by changing the pulling force of the BLS. The actuator with BLSs can improve the lateral stiffness by about 3.9 times compared to the one without BLSs. The maximum lateral stiffness can reach 0.46 N/mm. And the lateral stiffness can be modulated by decoupling about 1.3 times (e.g., from 0.35 to 0.46 N/mm when the bending angle is 45°). The test results show that the influence of the rigid structures on bending is small with about 1.5 mm maximum position errors of the distal point of the actuator in different pulling forces. The advantages brought by the proposed method enable versatile four-finger grasping. The performance of this gripper is characterized and demonstrated on multiscale, multiweight, and multimodal grasping tasks.

The platform for remote driving of a biomimetic propulsor and measurement of longitudinal and lateral forces generated by the propulsor

The performance characterization of a biomimetic propulsor for a swimming or flying robot typically requires measurement of the longitudinal and lateral forces generated by the propulsion of the propulsor. The propulsor can be either a tail (without or with a peduncle) or a morphing fin (wing), with multiple degrees of freedom (DOFs), and ideally the driving motors are designed to mount outside the propulsor to reduce the mass inertia and moment of inertia of the propulsor. In this article, we design and provide a robust and versatile platform that incorporate the mechanical two-DOFs lever unit and the measurement unit, as well as the configurable driving unit. The two-DOFs lever unit enables the freedoms of the longitudinal and lateral movements but are tightly constrained by the measurement unit that is fixed on the platform carriage for measurement of the longitudinal and lateral forces generated by the propulsor. The driving unit has the motors and the cable-driven modules that are configurable for bidirectional remote actuation, which is plug-and-play and flexible for different types and different numbers of motors. An experiment of the peduncle and the tail for propulsion is illustrated with this platform. The design here also serves as a design guidance for a platform for morphing wings.

Structure design and advantage research for bidirectional synchronous force-increasing EMB actuator

Electro-Mechanical Brake (EMB) can provide an ideal brake actuator for the active braking system of intelligent vehicles and the decoupled regenerative braking system of new energy vehicles. In order to solve the problem of large volume, weight, and axial size of the existing EMB actuator, a novel bidirectional synchronous force-increasing EMB (BSF-EMB) actuator scheme is proposed. Based on the maximum required braking force of the target vehicle under emergency braking conditions and the limitation of installation space in the wheel hub. The rotary motor and the ball screw are selected, the force-increasing mechanism parameters calculation and structure design are completed. In order to minimize the difference between the force-increasing ratio of the two-stage force-increasing mechanism and the lever force-increasing mechanism. The parameters of the force-increasing mechanism are optimized based on the weight adaptive particle swarm optimization algorithm. The three-dimensional model of the EMB actuator is established. In addition, when the required braking force is the same, the mass and volume of the BSF-EMB actuator can be decreased by about 43.4% and 55.8%, compared with the existing planetary gear force-increasing EMB (PGF-EMB) actuator scheme. Therefore, the BSF-EMB actuator can effectively decrease the unsprung mass of the vehicle and resolve the issue of limited installation space in the wheel hub of compact vehicles. The EMB models for two EMB actuator structures are built based on MATLAB/Simulink, and the EMB braking response speed and tracking performance of braking force are compared. The simulation results show that the braking response speed of the BSF-EMB actuator can be increased by 11%, 10.6%, 12.7%, and 14% compared to the PGF-EMB actuator under emergence braking condition and other three general service braking conditions, and the braking force adjustment is more precise. Finally, the effectiveness for the control strategy is verified by hardware in loop (HIL) experiment under sin wave input condition for braking force. The related research can provide reference for the design and application of EMB.

Repeatedly Programmable Liquid Crystal Dielectric Elastomer with Multimodal Actuation.

Dielectric elastomers (DEs) are actuatable under an electric field, whose large strain and fast response speed compare favorably with natural muscles. However, the actuation of DE-based devices is generally limited to a single mode and cannot be reconfigured after fabrication, which pales in comparison to biological counterparts given the ability to alter actuation modes according to external conditions. To address this, liquid crystal dielectric elastomers (LC-DEs) that can alter the dielectric actuation modes based on the thermally triggered shape-changing are prepared. Specifically, the two shapes through the LC phase transition possess different bending stiffness, which leads to distinct actuation modes after an electric field is applied. Moreover, the two shapes can be individually programmed/reprogrammed, that is, the one before the transition is regulated through force-directed solvent evaporation and the one after the transition is via bond exchange-enabled stress relaxation. As such, the multimodal dielectric actuation behaviors upon temperature change can be readily diversified. Meanwhile, the space charge mechanism endows LC-DEs with the significantly reduced driving e-field (8 V µm-1) and bidirectional actuation manners. It is believed this unique adaptivity in the actuation modes under a low electric field shall offer versatile designs for practical soft robots.

Design of auxetic cellular structures for in-plane response through out-of-plane actuation of stimuli-responsive bridge films

In this work, we propose novel designs of cellular structures exhibiting unconventional in-plane actuation responses to external stimuli. We strategically introduce stimuli-responsive bilayer bridge films within conventional honeycombs to achieve the desired actuation. The films are incorporated such that, in response to an external field (thermal, electric, chemical, etc), the bridge film bends out-of-plane, activating the honeycomb in the plane. The conventional out-of-plane deformation of the bridge film can lead to interesting and unconventional actuation in the plane. An analytical model of this coupled unit cell behavior is developed using curved beam theory, and the model is validated against finite element simulations. Several applications of such designs are presented. Unit cell architectures exhibiting both positive and negative macroscopic actuation are proposed, and the criterion for achieving such actuation is derived analytically. Furthermore, we demonstrate that by altering the topology, unidirectional and bidirectional negative actuation can be achieved. We also propose designs that result in the negative actuation of the structure with both monotonically increasing and monotonically decreasing stimuli. Finally, by combining two macroscopic structures with positive and negative actuation, we design actuators/sensors that bend in the plane in response to a stimulus.

Ultrafast Bi-Directional Bending Moisture-Responsive Soft Actuators through Superfine Silk Rod Modified Bio-Mimicking Hierarchical Layered Structure.

Development of stimulus-responsive materials is crucial for novel soft actuators. Among these actuators, the moisture-responsive actuators are known for their accessibility, eco-friendliness, and robust regenerative attributes. A major challenge of moisture-responsive soft actuators (MRSAs) is achieving significant bending curvature within short response times. Many plants naturally perform large deformation through a layered hierarchical structure in response to moisture stimuli. Drawing inspiration from the bionic structure of Delosperma nakurense (D. nakurense) seed capsule, here the fabrication of an ultrafast bi-directional bending MRSAs is reported. Combining a superfine silk fibroin rod (SFR) modified graphene oxide (GO) moisture-responsive layer with a moisture-inert layer ofreduced graphene oxide (RGO), this actuator demonstrated large bi-directional bending deformation (-4.06±0.09 to 10.44±0.00cm-1) and ultrafast bending rates (7.06cm-1s-1). The high deformation rate is achieved by incorporating the SFR into the moisture-responsive layers, facilitating rapid water transmission within the interlayer structure. The complex yet predictable deformations of this actuator are demonstrated that can be utilized in smart switch, robotic arms, and walking device. The proposed SFR modification method is simple and versatile, enhancing the functionality of hierarchical layered actuators. It holds the potential to advance intelligent soft robots for application in confined environments.

Design, modeling, and control of a novel soft-rigid knee joint robot for assisting motion

AbstractThis paper presents the design, modeling, and control of a novel soft-rigid knee joint robot (SR-KR) for assisting motion. SR-KR is proposed to assist patients with knee joint injuries conducting gait training and completing walking movements. SR-KR consists of a novel soft-rigid bidirectional curl actuator, a thigh clamping structure, and a crus clamping structure. The actuating part of SR-KR is composed of soft materials, which ensures the wearing comfort and safety, while the wearing parts contain rigid structure, which ensures the efficient transmission of torque. The bending deformation model of SR-KR is established, which reveal the relationship among SR-KR’s bending curvature, working pressure, and output torque. Experiments show that SR-KR can provide more than 26.3 Nm torque for knee joint motion in human gait range. A double closed loop servo control system including attitude servo and pressure servo is built to better apply SR-KR. Mechanical property test, trajectory-driven test, and lower limb wearing test have been conducted, which show that SR-KR has ability to assist in lower limb motion and has potential in the fields of rehabilitation and human enhancement.

Experiments and study of a low-frequency, high-speed bi-directional piezoelectric stick-slip actuator

Experiments and study of a low-frequency, high-speed bi-directional piezoelectric stick-slip actuator

Piezoelectric actuation combined with ultrasound for enhancing drug delivery in gastric mucosa phantom in vitro

In recent years, treatments for gastrointestinal malignant tumors have attracted a lot of attention. However, due to size limitations and the working environment of gastrointestinal peristalsis, traditional treatment methods have poor efficacy. Herein, we proposed a novel drug release method of piezoelectric actuation combined with ultrasound in the endoscope biopsy channel. A bidirectional piezoelectric actuator was manufactured and inserted into the endoscope with an ultrasonic transducer, adjusting the distance between the transducer and the lesion. A gastric mucosa phantom was fabricated and a finite element (FE) model was established for ultrasound thermal calculation. For enhancing the drug release rate, a pulse-echo method was conducted using a Laboratory Virtual Instrument Engineering Workbench (LabVIEW) program for real-time monitoring and feedback. The results of FEM calculations show that the temperature in the phantom can reach the melting-phase transition temperature of the TSL (41 ± 1 °C). The drug release rate can increase from 2.2 × 10−4 mg min−1 to 39.2 × 10−4 mg min−1 with our actuator, the latter is nearly 18 times the former. Furthermore, the drug release rate can be increased to a maximum value of 45.8 × 10−4 mg min−1 by optimizing the driving parameter of our actuator. Therefore, our method has a bright application in targeted drug delivery of major gastrointestinal diseases in the future.

Multi-stimuli-responsive Ti3C2TX MXene-based actuators actualizing intelligent interpretation of traditional shadow play

For smart devices, there is a growing demand for multi-functional soft actuators, nevertheless, well-developed actuators always respond to single stimulus, and it is still challenging to achieve the application diversity standards. Herein, a bidirectional multi-stimuli responsive soft actuator based on Ti3C2TX MXene-cellulose nanowhiskers (CNWs)-polyvinyl alcohol (PVA)/polydimethylsiloxane (PDMS) multilayer membranes is proposed (MXCP-P). By grafting CNWs onto MXene nanosheets, a freestanding composite film with gradient layered structure was prepared. Due to the hygroscopicity among MXene nanosheets, increased interlayer space is in favor of adsorption/desorption of water molecules, causing invertible shape change and humidity-driven deformation with a rapid response. Based on high photothermal conversion capacity of MXene and large difference of coefficient of thermal expansion between PDMS and MXene, the MXCP-P achieves an ultra-large amplitude and fast response driven by natural light. A Venus flytrap soft robot is constructed with good actuation behaviors. The MXCP-P film was employed as actuators in the opera of The Male Phoenix Pursui from Han Dynasty and in shadow puppetry “Monkey King Subdus the White-Bone Demon” of China, both exhibiting excellent performances towards humidity and light stimuli synchronously. This paper inspires a new strategy for multi-stimuli responsive soft bionic robots and intelligent traditional shadow play.

Electrospun Nanofibrous UV Filters with Bidirectional Actuation Properties Based on Salmon Sperm DNA/Silk Fibroin for Biomedical Applications.

In this study, we dissolved Bombyx mori degummed silk [i.e., silk fibroin (SF)] and salmon sperm deoxyribonucleic acid (DNA) in water and used a bioinspired spinning process to obtain an electrospun nanofibrous SF-based patch (ESF). We investigated the bidirectional macroscale actuation behavior of ESF in response to water vapor and its UV-blocking properties as well as those of ESF/DNA films. Fourier transform infrared (FTIR) results suggest that the formation of β-sheet-rich structures promotes the actuation effect. ESF/DNA film with high-ordered and β-sheet-rich structures exhibits higher electrical conductivity and is water-insoluble. Given the intrinsic ability of both SF and DNA to absorb UV radiation, we performed biological experiments on the viability of keratinocyte HaCaT cells after exposure to solar spectrum components. Our findings indicate that the ESF/DNA patch is photoprotective and can increase the cellular viability of keratinocytes after UV exposure. Furthermore, we demonstrated that ESF/DNA patches treated with water vapor can serve as suitable scaffolds for tissue engineering and can improve tissue regeneration when cellularized with HaCaT cells. The 3D shape morphing capability of these patches, along with their potential as UV filters, could offer significant practical advantages in tissue engineering.

Ultrathin internal dielectric electrostatic actuator for reduced pull-in voltage and bidirectional actuation

Direction and analog deflection control, as well as low voltage digital switching are the most desirable attributes in electrostatic actuators for current MEMS applications. In this work we show how internal dielectric transduction can be used to reduce pull-in voltages without reducing the air gap, and to effect bi-directional actuation. The actuator is a metal–dielectric–metal sandwich. For hybrid actuation to achieve reduced pull-in, the device has a thick bottom metal and a thin top metal, while for the upward actuator the device has a thick top metal and a thin bottom metal. An out-of-plane deflection of 108 nm is achieved using 5 V applied voltage for the upward actuator, while the hybrid actuator shows over 50% reduction in pull-in voltage from 1.26 V to 0.62 V.