Actuation Approach Research Articles

External Steering of Vine Robots via Magnetic Actuation.

This article explores the concept of external magnetic control for vine robots to enable their high curvature steering and navigation for use in endoluminal applications. Vine robots, inspired by natural growth and locomotion strategies, present unique shape adaptation capabilities that allow passive deformation around obstacles. However, without additional steering mechanisms, they lack the ability to actively select the desired direction of growth. The principles of magnetically steered growing robots are discussed, and experimental results showcase the effectiveness of the proposed magnetic actuation approach. We present a 25-mm-diameter vine robot with an integrated magnetic tip capsule, including 6 degrees of freedom (DOF) localization system and camera, and demonstrate a minimum bending radius of 3.85 cm with an internal pressure of 30 kPa. Furthermore, we evaluate the robot's ability to form tight curvature through complex navigation tasks, with magnetic actuation allowing for extended free-space navigation without buckling. The suspension of the magnetic tip was also validated using the 6 DOF localization system to ensure that the shear-free nature of vine robots was preserved. Additionally, by exploiting the magnetic wrench at the tip, we showcase preliminary results of vine retraction. The findings contribute to the development of controllable vine robots for endoluminal applications, providing high tip force and shear-free navigation.

Towards Implantable Artificial Muscles: Epoxy Based Bilayer Thermal Actuators with Ambient Activation Temperatures

AbstractThe development of soft and biocompatible actuators is a current challenge in the fast‐growing field of soft robotics. A variety of shape‐memory and thermal actuators are currently being explored for application in these areas, especially to produce actuators that can operate at biocompatible temperatures for in vivo applications. Here we detail the synthesis of epoxy based materials, a class of materials not fully explored for soft actuators. By careful tuning of polymer composition by variation of monomer feed ratios, we show tuneable glass transition temperatures (Tgs) of these materials. Ambient temperature (30–60 °C) thermal actuators were then realised by casting of bilayers of epoxy resins with varying Tgs. Differences in thermal expansion when the Tg was reached lead to actuation in a specific direction. With optimisation, actuation in both the external‐heated and joule‐heated NiChrome‐epoxy actuators were able to occur at physiological temperatures (36–40 °C), previously unreported in the literature. For the joule‐heated NiChrome–epoxy actuators surface temperatures remained under 40 °C during actuation at low operating voltages (<2 V). Higher force and power output could be achieved in a repeatable fashion at higher driving voltages without loss of displacement, but also leading to higher surface temperatures. These materials and the actuation approach present an exciting opportunity to develop future implantable actuators to solve significant challenges related to quality of life and an ageing population.

The Design and Investigation of Hybrid a Microfluidic Micromixer

Today, microfluidics has become a revolutionary interdisciplinary topic with considerable attention in a wide range of biotechnology applications. In this research work, a numerical investigation of a microfluidic micromixer is carried out using a hybrid actuation approach with different micropillar shapes and gaps. For this purpose, COMSOL Multiphysics v.5.2. is used with three different physics, such as thermoviscous acoustic physics to solve acoustic governing equations, laminar physics to solve fluid flow governing equations, and diluted transport species to solve mixing governing equations. The simulations were carried out at different Reynolds numbers such as 2, 4, 6, 8, 10, and 12 with an oscillation frequency of 15 kHz. The results were in the form of acoustic characteristics such as acoustic pressure, acoustic velocity, acoustic stream, mixing index, and fluid flow behaviour at various Reynolds numbers. The results revealed that the inclusion of micropillars improved the mixing performance and strength of the acoustic field, resulting in an improvement of the mixing performance compared to the case without micropillars. In addition, the mixing performance is also investigated at different Reynolds numbers, and a higher mixing index is investigated at lower Reynolds numbers. Moreover, it was also investigated that blade-shaped micropillars with 0.150 mm gaps deliver the best results compared to the other cases, and the maximum and minimum values of the mixing index are 0.97 and 0.72, respectively, at Reynolds number 2. The main reason behind this larger mixing index at low Reynolds numbers is due to the inclusion of micropillars that enhance the diffusion rate and contact area, leading to the homogenisation of the heterogeneous fluids in the microchamber. The obtained results can be extremely helpful for the design and modifications of a hybrid microfluidics micromixer.

Simulation-Driven Universal Surrogates of Coupled Mechanical Systems: Real-Time Simulation of a Forestry Crane

Abstract Preparing simulation-driven surrogates for a coupled mechanical system can be challenging because the associated mechanical and actuator dynamics demand high-fidelity numerical solutions. Proposed here is a universal hydraulic surrogate (UHS), which can provide solutions to high-fidelity mechanical systems with a universal actuator in a surrogate-assisted monolithic approach. The UHS acts as an alternative to the standard lumped fluid theory by eliminating the hydraulic pressures differential equations. A surrogate-assisted universal actuator uses an approximated model to define hydraulic force in high-fidelity mechanical systems. The approximated force model was developed through training against the dynamics of a one-dimensional (1D) hydraulic cylinder and spring-damper. A covariance matrix adaption evolutionary strategy (CMA-ES) was used as an optimization algorithm to minimize differences between the standard dynamics and UHS approaches at the position and velocity levels. The robustness of resulting UHS was validated to predict the behaviors of the simple four-bar mechanism and the forestry crane. The focus was on numerical accuracy and computational efficiency. The maximum percent normalized root mean square error (PN-RMSE) between the states of the approximated force model and lumped fluid theory were approximately 2.04% and 6.95%, respectively. The proposed method was approximately 52 times faster than the standard lumped fluid theory method. By providing accurate predictions outside the training data, the simulation-driven UHS promises better computational performance leading to real-time simulation solutions for the coupled mechanical systems. The UHS can be applied in simulation, optimization, control, state and parameter estimation, and Artificial Intelligence (AI) implementations for coupled mechanical systems.

Fingertip dynamic response simulated across excitation points and frequencies

Predicting how the fingertip will mechanically respond to different stimuli can help explain human haptic perception and enable improvements to actuation approaches such as ultrasonic mid-air haptics. This study addresses this goal using high-fidelity 3D finite element analyses. We compute the deformation profiles and amplitudes caused by harmonic forces applied in the normal direction at four locations: the center of the finger pad, the side of the finger, the tip of the finger, and the oblique midpoint of these three sites. The excitation frequency is swept from 2.5 to 260 Hz. The simulated frequency response functions (FRFs) obtained for displacement demonstrate that the relative magnitudes of the deformations elicited by stimulating at each of these four locations greatly depend on whether only the excitation point or the entire finger is considered. The point force that induces the smallest local deformation can even cause the largest overall deformation at certain frequency intervals. Above 225 Hz, oblique excitation produces larger mean displacement amplitudes than the other three forces due to excitation of multiple modes involving diagonal deformation. These simulation results give novel insights into the combined influence of excitation location and frequency on the fingertip dynamic response, potentially facilitating the design of future vibration feedback devices.

Nature-inspired miniaturized magnetic soft robotic swimmers

State-of-the-art biomedical applications such as targeted drug delivery and laparoscopic surgery are extremely challenging because of the small length scales, the requirements of wireless manipulation, operational accuracy, and precise localization. In this regard, miniaturized magnetic soft robotic swimmers (MSRS) are attractive candidates since they offer a contactless mode of operation for precise path maneuvering. Inspired by nature, researchers have designed these small-scale intelligent machines to demonstrate enhanced swimming performance through viscous fluidic media using different modes of propulsion. In this review paper, we identify and classify nature-inspired basic swimming modes that have been optimized over large evolutionary timescales. For example, ciliary swimmers like Paramecium and Coleps are covered with tiny hairlike filaments (cilia) that beat rhythmically using coordinated wave movements for propulsion and to gather food. Undulatory swimmers such as spermatozoa and midge larvae use traveling body waves to push the surrounding fluid for effective propulsion through highly viscous environments. Helical swimmers like bacteria rotate their slender whiskers (flagella) for locomotion through stagnant viscid fluids. Essentially, all the three modes of swimming employ nonreciprocal motion to achieve spatial asymmetry. We provide a mechanistic understanding of magnetic-field-induced spatiotemporal symmetry-breaking principles adopted by MSRS for the effective propulsion at such small length scales. Furthermore, theoretical and computational tools that can precisely predict the magnetically driven large deformation fluid–structure interaction of these MSRS are discussed. Here, we present a holistic descriptive review of the recent developments in these smart material systems covering the wide spectrum of their fabrication techniques, nature-inspired design, biomedical applications, swimming strategies, magnetic actuation, and modeling approaches. Finally, we present the future prospects of these promising material systems. Specifically, synchronous tracking and noninvasive imaging of these external agents during in vivo clinical applications still remains a daunting task. Furthermore, their experimental demonstrations have mostly been limited to in vitro and ex vivo phantom models where the dynamics of the testing conditions are quite different compared the in vivo conditions. Additionally, multi-shape morphing and multi-stimuli-responsive modalities of these active structures demand further advancements in 4D printing avenues. Their multi-state configuration as an active solid-fluid continuum would require the development of multi-scale models. Eventually, adding multiple levels of intelligence would enhance their adaptivity, functionalities, and reliability during critical biomedical applications.

Air-Coupled Broadband Impact-Echo Actuation Using Supersonic Jet Flow

The impact-echo method (IE) is a non-destructive testing method commonly used in civil engineering. We propose a completely new approach for air-coupled actuation based on supersonic jet flow. The impinging jet sound generates continuously high sound pressures with a broad frequency bandwidth. This novel concept of utilising aeroacoustic sound for air-coupled IE was evaluated on two concrete specimens and validated using a classical IE device with physical contact. The results show a high agreement with the expected frequencies. Delaminations are correctly detected in depth and size. This proves the high reliability of air-coupled IE based on supersonic jet flow.Graphic abstract

Design Optimization of Piezocomposites Using a Homogenization Model: From Analytical Model to Experimentation.

In the process of activating non-conductive smart-structures using piezoelectric patches, one possible method is to add a conductive layer to ensure electrical contact of both electrodes of the ceramic. Therefore, depending on the stiffness and the thickness of this layer, changes in the overall piezoelectric properties lead to a loss in the electromechanical coupling that can be implemented. The purpose of this work is to study the impact of this added electrode layer depending on its thickness. A model of the effect of this layer on the piezoelectrical coefficients has been derived from the previous approach of Hashimoto and Yamagushi and successfully compared to experimental data. This global model computes the variation of all the piezoelectric coefficients, and more precisely of k31 or d31 for various brass electrode volumes relative to the ceramic volume. A decrease in the lateral electromechanical coupling factor k31 was observed and quantified. NAVY II PZT piezoelectric transducers were characterized using IEEE standard methods, with brass electrode thicknesses ranging from 50 to 400 microns. The model fits very well as shown by the results, leading to good expectations for the use of this design approach for actuators or sensors embedded in smart-structures.

SonoTransformers: Transformable acoustically activated wireless microscale machines

Shape transformation, a key mechanism for organismal survival and adaptation, has gained importance in developing synthetic shape-shifting systems with diverse applications ranging from robotics to bioengineering. However, designing and controlling microscale shape-shifting materials remains a fundamental challenge in various actuation modalities. As materials and structures are scaled down to the microscale, they often exhibit size-dependent characteristics, and the underlying physical mechanisms can be significantly affected or rendered ineffective. Additionally, surface forces such as van der Waals forces and electrostatic forces become dominant at the microscale, resulting in stiction and adhesion between small structures, making them fracture and more difficult to deform. Furthermore, despite various actuation approaches, acoustics have received limited attention despite their potential advantages. Here, we introduce "SonoTransformer," the acoustically activated micromachine that delivers shape transformability using preprogrammed soft hinges with different stiffnesses. When exposed to an acoustic field, these hinges concentrate sound energy through intensified oscillation and provide the necessary force and torque for the transformation of the entire micromachine within milliseconds. We have created machine designs to predetermine the folding state, enabling precise programming and customization of the acoustic transformation. Additionally, we have shown selective shape transformable microrobots by adjusting acoustic power, realizing high degrees of control and functional versatility. Our findings open new research avenues in acoustics, physics, and soft matter, offering new design paradigms and development opportunities in robotics, metamaterials, adaptive optics, flexible electronics, and microtechnology.

Reversible shape transition of nanostructure-induced bistable shells based on pneumatic actuations

Shape reconfiguration is a crucial feature in aerodynamic applications of bistable shells, especially for nanostructure-induced bistable shells, which offer good load-bearing capacities. Traditional actuation methods using smart materials are not powerful enough to trigger the transition of the nanostructured bistable shells. This study proposes a pneumatic actuation approach based on analytical and numerical investigations on their transition characteristics. Two distinct transition paths are theoretically identified, dependent on the nanostructured region ratio and pneumatic region ratio. With the guidance from the theoretical models, custom-made pneumatic suction cups are employed to achieve wireless and automatic reconfigurations of the nanostructured bistable shells. This pneumatic shape morphing provides a valuable approach for creating adaptive surfaces in aerodynamic applications.

Multiple Magneto-Optical Microrobotic Collectives with Selective Control in Three Dimensions Under Water.

Inspired by natural swarms, various methods are developed to create artificial magnetic microrobotic collectives. However, these magnetic collectives typically receive identical control inputs from a common external magnetic field, limiting their ability to operate independently. And they often rely on interfaces or boundaries for controlled movement, posing challenges for independent, three-dimensional(3D) navigation of multiple magnetic collectives. To address this challenge, self-assembled microrobotic collectives are proposed that can be selectively actuated in a combination of external magnetic and optical fields. By harnessing both actuation methods, the constraints of single actuation approaches are overcome. The magnetic field excites the self-assembly of colloids and maintains the self-assembled microrobotic collectives without disassembly, while the optical field drives selected microrobotic collectives to perform different tasks. The proposed magnetic-photo microrobotic collectives can achieve independent position and path control in the two-dimensional (2D) plane and 3D space. With this selective control strategy, the microrobotic collectives can cooperate in convection and mixing the dye in a confined space. The results present a systematic approach for realizing selective control of multiple microrobotic collectives, which can address multitasking requirements in complex environments.

Self‐Sustained and Coordinated Rhythmic Deformations with SMA for Controller‐Free Locomotion

This study presents a modular, electronics‐free, and fully onboard control and actuation approach for shape memory alloy (SMA)‐based soft robots to achieve locomotion tasks. This approach exploits the nonlinear mechanics of compliant curved beams and carefully designed mechanical control circuits to create and synchronize rhythmic deformation cycles, mimicking the central pattern generators prevalent in animal locomotions. More specifically, the study elucidates a new strategy to amplify the actuation performance of the shape memory coil actuator by coupling it to a carefully designed, monostable curve beam with a snap‐through buckling behavior. Such SMA‐curved beam assembly is integrated with an entirely mechanical circuit featuring a slider mechanism. This circuit can automatically cut off and supply current to the SMA according to its deformation status, generating a self‐sustained rhythmic deformation cycle using a simple DC power supply. Finally, this study presents a new strategy to coordinate (synchronize) two rhythmic deformation cycles from two robotic modules to achieve efficient crawling locomotion but still use a single DC power. This work represents a significant step toward fully autonomous, electronics‐free SMA‐based locomotion robots with fully onboard actuation and control.

Aeroengine Actuator Fault Detection and Estimation Via Combined Model Observers

Accurate diagnosis of faults in aeroengines is crucial for enhancing reliability and reducing operational and maintenance costs. This paper proposes a fault diagnosis approach for aeroengine actuators that utilizes a combination of model observers. Firstly, the faults of aeroengine actuators are described, and their representation as Aero-engine State Variable Model (SVM) is elaborated on. Secondly, a Luneberger model observer is designed to detect actuator faults using observer residuals. Thirdly, Adaptive Thau Observers (ATO) are developed to accurately estimate the offset value of actuator faults. Finally, the proposed fault diagnostics solution is tested and validated using a benchmark aeroengine model-CMAPSS 40. Fault diagnostics results under two fault scenarios demonstrate the Effectiveness of the proposed approach.

Soft Optical Waveguides for Biomedical Applications, Wearable Devices, and Soft Robotics: A Review

In the domains of biomedical applications, wearable devices, and soft robotics, recent advancements have underscored the potential of soft, stretchable, and biocompatible devices. The design of optical soft devices has emerged as an ideal candidate for many applications owing to their high flexibility and immunity to electromagnetic interference. In this review, recent advances in soft optical waveguides, including advanced material selection, fabrication strategies, and characterization, are discussed. Herein, a comprehensive summary of the soft‐waveguide sensing strategies and actuation approaches are provided. Furthermore, the extensive applications of soft optical waveguides in the fields of biomedicine, wearable devices, and soft robotics are explored. Lastly, the challenges and opportunities for the future of soft optical waveguides, including multimodal sensing, algorithm optimization, and manufacturing scalability, are discussed.

Triple-Responsive Soft Actuator with Plastically Retentive Deformation and Magnetically Programmable Recovery.

Multistimuli responsiveness and programmable shape recovery are crucial for soft actuators in soft robotics, electronics, and wearables. However, existing strategies for actuation cannot attain power-free shape retention after removing the external energy supply. Here, a self-assembled density deposition method was developed to fabricate an electrothermal-NIR-magnetic triple-response actuator which was composed of cellulose nanofiber/poly(vinyl alcohol)/liquid metal (CNF/PVA/LM) and magnetic polydimethylsiloxane (MPDMS) layer. Interestingly, the large deformation can be controllably fixed and the temporary configuration will be programmable recovered under a magnetic field due to the thermal-plastic transferring behavior of the CNF/PVA/LM. Rolling robot prepared based on soft actuators exhibits good ability to avoid obstacles. In addition, the object handling and programmable release capabilities of the carrier robots demonstrate that this actuation approach will contribute to a better understanding of how to more rationally utilize various stimuli for application purposes.

Diagnostic Signal Method for Fault Identification of Electro-Hydraulic Servo Actuators

In this paper, we develop a fault identification approach for electro-hydraulic servo actuators based on injecting a pre-defined diagnostic signal into the system and then extracting fault-related features from the phase space topology. Next, we build regression models using an artificial neural network, which maps the feature space to fault space to identify the faults represented by the system’s parameters. The performance of the proposed fault identification approach is evaluated when the degradation of permanent armature occurs. The effect of parametric faults on the dynamics is studied and discussed. The different excitation of the system is considered, and the robustness of the proposed method under the condition of noise is also explored. The obtained results indicate the effectiveness of injected diagnostic signals in enriching the dynamics of the system and increasing the quality of extracted features and the accuracy of trained artificial neural networks.

Hybrid-excited magneto-responsive soft actuators for grasping and manipulation of objects

Magneto-responsive soft actuators have attracted significant attention due to their non-contact nature and exceptional responsiveness. However, existing actuation methods relying on a single magnetic source, such as permanent magnets or electromagnets, suffer from an imbalance between flexible regulation and low energy operation. In this study, we propose a novel hybrid-excited magnetic actuation approach that leverages the synergy between permanent magnets and electromagnets. By utilizing the static magnetic field generated by permanent magnets to stabilize the deformation state of soft actuators, and employing the pulsed magnetic field generated by electromagnets to regulate the deformation, we achieve a harmonious combination of flexibility and energy efficiency. Furthermore, we introduce a two-step magnetization method that enhances the deformability of multi-arm soft actuators, enabling complete closure after deformation. To exemplify the practical implications, we develop a magnetic soft gripper system capable of versatile object manipulation, offering precise control over the grasping and releasing processes without the need for electrical energy consumption. Experimental results demonstrate the exceptional performance of the soft gripper, including a high lifting ratio (larger than 50), fast (<0.05s) and adjustable response. Moreover, we substantiate its potential in real-world scenarios through targeted delivery of single objects with different physical features and simultaneous manipulation of multiple objects with selective capability. This research presents a significant advancement in the field of magneto-responsive soft actuators, offering novel design principles, improved performance, and promising applications across various domains.

Fusion Hybrid Linear Actuator: Concept and Disturbance Resistance Evaluation

The response of robot actuators to various dynamic interactions during contact tasks is not trivial because there exists a tradeoff between actuator-thrust force density and back-drivability. Although hybrid actuation approaches are promising, complex transmission mechanisms are necessary to synthesize forces from heterogeneous actuators. This study presents a novel concept of a fusion hybrid linear actuator to address the fundamental problems in conventional hybrid actuation approaches. The concept embodies an integrated structure of an air cylinder and a linear motor and shares the moving spaces of the piston and moving part of the linear motor inside the compact housing of the actuator. Herein, the design strategy requirements and its structural optimization processes are discussed. A kinetic friction model of a pneumatic cylinder that considers a piston structure is proposed to improve the force characteristics during dynamic interaction. Furthermore, a quantitative benchmark test is developed to maintain the contact force constant against a load actuator, to evaluate the disturbance resistance under a wide range of target contact force conditions. The concept and performance were validated by experiments comparing the proposed hybrid actuation condition with conventional pneumatic actuation conditions.

A Compliant Manipulator for Confined Space Tissue Diagnostics: Kinematic and Force Analyses and Initial Characterization Experiments

Abstract Minimally invasive procedures employ continuum manipulators, however internal human anatomy presents challenges relating to size, dexterity, and workspace for these manipulators. This manuscript presents modeling, kinematic analysis, prototyping, and characterization of a micro-robotic manipulator for transurethral palpation of bladder tissue. The proposed micro-robot consists of two subsystems: a tendon-driven continuum segment with an elastic tube encompassing each joint for compliance and structural integrity, and a hyper-spherical joint ensuring higher dexterity and manipulability with a comprehensive actuation and modeling approach. The forward kinematics follow the Denavit-Hartenberg formulation. A developed differential Jacobian inverse kinematics formulation prevents motion singularities for desired poses while operating in the confined space. The simulated kinematic results confirm the dexterity and reach of the proposed micro-robot. A strain energy quasi-static model is developed for a single continuum module. The model is evaluated for tension-bend angle relationships as function of tube material and geometry, and joint length. Limited functionality continuum modules (4mm outside diameter) with four different joint lengths, (3, 6, 9, 12) mm, are prototyped for tension-bend angle characterization using a computer vision outfitted experimental setup. An equivalent shear modulus relationship for the elastic tube for selected joint length values and bend angles is developed using experimental results. The tension-bend angle response is nonlinear and function of tube properties, joint geometry, and their interactions. The comparison of the experimental and quasi-static model results shows high fidelity for use in predicting the robot continuum segment behavior.

Wireless Power Transfer to Electrothermal Liquid Crystal Elastomer Actuators.

Wireless actuation of electrically driven soft actuators is of paramount importance for the development of bioinspired soft robotics without physical connection or on-board batteries. Here, we demonstrate untethered electrothermal liquid crystal elastomer (LCE) actuators based on emerging wireless power transfer (WPT) technology. We first design and fabricate electrothermal LCE-based soft actuators that consist of an active LCE layer, a conductive liquid metal-filled polyacrylic acid (LM-PA) layer, and a passive polyimide layer. LM can function not only as an electrothermal transducer to endow resulting soft actuators with electrothermal responsiveness but also as an embedded sensor to track the resistance changes. Various shape-morphing and locomotive modes such as directional bending, chiral helical deformation, and inchworm-inspired crawling can be facilely obtained through appropriately controlling the molecular alignment direction of monodomain LCEs, and the reversible shape-deformation behaviors of resulting soft actuators can be monitored in real-time through resistance changes. Interestingly, untethered electrothermal LCE-based soft actuators have been achieved by designing a closed conductive LM circuit within the actuators and combining it with inductive-coupling WPT technology. When the resulting soft actuator approaches a commercially available wireless power supply system, an induced electromotive force can be generated within the closed LM circuit, which results in Joule heating and wireless actuation. As proof-of-concept illustrations, wirelessly driven soft actuators that can exhibit programmable shape-morphing behaviors are demonstrated. The research disclosed herein can provide insights into the development of bioinspired somatosensory soft actuators, battery-free wireless soft robots, and beyond.