Actuation Capabilities Research Articles

Manufacturing thin ionic polymer metal composite for sensing at the microscale

Ionic polymer metal composites (IPMCs) are a class of materials with a rising appeal in biological micro-electromechanical systems (bio-MEMS) due to their unique properties (low voltage output, bio-compatibility, affinity with ionic medium). While tailoring and improving actuation capabilities of IPMCs is a key motivator in almost all IPMC manufacturing reports, very little efforts have been dedicated to sensing using IPMC thinner than 100 µm. Most reports on IPMC manufacturing and utilization rely on 180 µm-thick Nafion with platinum electrodes, too stiff for bio-MEMS applications. The same fabrication process on thinner membranes does yield in very poor electrodes and performance, and needs to be studied to increase flexibility and sensitivity in the microscale range. This study demonstrates an electroless Pt deposition method for fabricating bio-MEMS-suitable 50 µm-thick IPMC samples. First, we perform a comparative study on the platinum distribution within the Nafion backbone as well as on the surface for the standard electroless deposition recipe for thin (50 µm) and thick (180 µm) Nafion. We report strong differences in platinum distribution for thick and thin IPMC that experienced the same manufacturing process. By varying chemical concentrations from the standard recipe we obtain convenient platinum distribution on thin Nafion, with platinum mainly localized in proximity of surface, as well as electrodes with lower sheet resistance. We could measure the flexural rigidity as N·m2, 46 times lower than standard 180 µm-thick IPMC. The calculated sensitivity is 0.476 ± 0.02 mV mm−1 and the limit of detection for our sensor is 500 ± 20 µm. This procedure sets a milestone for manufacturing 50 µm-thick IPMC for transducers and sensors in bio-MEMS applications.

Self-Aware Artificial Coiled Yarn Muscles with Enhanced Electrical Conductivity and Durability via a Two-Step Process.

Muscles are capable of modulating the body and adapting to environmental changes with a highly integrated sensing and actuation. Inspired by biological muscles, coiled/twisted fibers are adopted that can convert volume expansion into axial contraction and offer the advantages of flexibility and light weight. However, the sensing-actuation integrated fish line/yarn-based artificial muscles are still barely reported due to the poor actuation-sensing interface with off-the-shelf fibers. We report herein artificial coiled yarn muscles with self-sensing and actuation functions using the commercially available yarns. Via a two-step process, the artificial coiled yarn muscles are proved to obtain enhanced electrical conductivity and durability, which facilitates the long-term application in human-robot interfaces. The resistivity is successfully reduced from 172.39 Ω·cm (first step) to 1.27 Ω·cm (second step). The multimode sense of stretch strain, pressure, and actuation-sensing are analyzed and proved to have good linearity, stability and durability. The muscles could achieve a sensitivity (gauge factor, GF) of the contraction strain perception up to 1.5. We further demonstrate this self-aware artificial coiled yarn muscles could empower non-active objects with actuation and real-time monitoring capabilities without causing damage to the objects. Overall, this work provides a facile and versatile tool in improving the actuation-sensing performances of the artificial coiled yarn muscles and has the potential in building smart and interactive soft actuation systems.

An at-scale tailless flapping wing hummingbird robot: II. Flight control in hovering and trajectory tracking

Flight control such as stable hovering and trajectory tracking of tailless flapping-wing micro aerial vehicles is a challenging task. Given the constraint on actuation capability, flight control authority is limited beyond sufficient lift generation. In addition, the highly nonlinear and inherently unstable vehicle dynamics, unsteady aerodynamics, wing motion caused body oscillations, and mechanism asymmetries and imperfections due to fabrication process, all pose challenges to flight control. In this work, we propose a systematic onboard control method to address such challenges. In particular, with a systematic comparative study, a nonlinear flight controller incorporating parameter adaptation and robust control demonstrates the preferred performances. Such a controller is designed to address time-varying system uncertainty in flapping flight. The proposed controller is validated on a 12-g at-scale tailless hummingbird robot equipped with two actuators. Maneuver experiments have been successfully performed by the proposed hummingbird robot, including stable hovering, waypoint and trajectory tracking, and stabilization under severe wing asymmetries.

Design and Characterization of Multifunctional SMART Materials for Sensing and Actuation Applications

The field of materials science has experienced significant advancements, leading to the emergence of multifunctional SMART (Sensing, Measuring, Actuation, and Responsive Technologies) materials. These materials possess a distinctive set of properties that allow them to detect alterations in their surroundings and react accordingly by employing customised actuation mechanisms. The current study provides a full exposition on the design, synthesis, and characterisation of multifunctional SMART materials, with a specific focus on their applications in sensing and actuation. The design process include the meticulous identification and incorporation of diverse functional components, including piezoelectric materials, shape memory alloys, electroactive polymers, and nanomaterials, inside a composite matrix. The selection of these components is based on their unique physical and chemical characteristics, which enable them to detect external stimuli and demonstrate response behaviours. The amalgamation of various constituents inside a unified material framework yields a synergistic outcome, hence augmenting the holistic functionality of the SMART material. The research also explores the many uses of multifunctional SMART materials, encompassing areas such as structural health monitoring and biological devices. The capacity of these materials to detect alterations in temperature, strain, pressure, and other environmental factors, in conjunction with their actuation capabilities, presents novel opportunities for advancement in several disciplines.

Photomechanical response under physiological conditions of azobenzene-containing 4D-printed liquid crystal elastomer actuators.

Soft and mechanically responsive actuators hold the promise to revolutionize the design and manufacturing of devices in the areas of microfluidics, soft robotics and biomedical engineering. In many of these applications, the actuators need to operate in a wet environment that can strongly affect their performance. In this paper, we report on the photomechanical response in a biological buffer of azobenzene-containing liquid crystal elastomer (LCE)-based actuators, prepared by four-dimensional (4D) printing. Although the photothermal contribution to the photoresponse is largely cancelled by the heat withdrawing capacity of the employed buffer, a significant photoinduced reversible contraction, in the range of 7% of its initial length, has been achieved under load, taking just a few seconds to reach half of the maximum contraction. Effective photomechanical work performance under physiological conditions has, therefore, been demonstrated in the 4D-printed actuators. Advantageously, the photomechanical response is not sensitive to salts present in the buffer differently to hydrogels with responses highly dependent on the fluid composition. Our work highlights the capabilities of photomechanical actuators, created using 4D printing, when operating under physiological conditions, thus showing their potential for application in the microfluidics and biomedical fields.

Experimental investigations for the characterisation of an SMA-bias spring actuator in a flexible tube manipulator

The present article describes an application of shape memory alloy (SMA) spring-based actuator for the development of a flexible tube manipulator intended for tumour irradiation application. A constitutive model is proposed that incorporates the nonlinearity of SMA spring along with the loading history of material and predicts 4 N as the force generation capability of the SMA-bias spring actuator. The simulation results follow the characteristic profile of SMA in both normal as well as cyclic loading conditions. Further, experimental characterisation of the actuator is carried out to determine various parameters like modulus of rigidity, critical shear stresses, etc. and a proportional integral derivative (PID) controller is experimentally implemented which made the tip of the tube following a series of predefined points. The maximum positional error is around 5%, which shows the positional tracking ability of the developed manipulator and the maximum bending angle of the tube is 74.6°.

Sensor-Based Planning and Control for Robotic Systems: Introducing Clarity and Perceivability

In this paper, we first introduce an information measure, termed clarity, motivated by information entropy, and show that it has intuitive properties relevant to dynamic coverage control and informative path planning. Clarity defines on a scale of [0, 1] the quality of the information that we have about a variable of interest in an environment. Clarity lower bounds the expected estimation error of any estimator, and is used as the information metric in the notion of perceivability, which is defined later on and is the primary contribution of the paper. Perceivability captures whether a given robotic (or more generally, sensing and control) system has sufficient sensing and actuation capabilities to gather desired information about an environment. We show that perceivability relates to the reachability of an augmented system, which encompasses the robot dynamics and the clarity about the environment, and we derive the corresponding Hamilton-Jacobi-Bellman equations. Thus, we provide an algorithm to measure an environment’s perceivability, and obtain optimal controllers that maximize information gain. In simulations, we demonstrate how clarity is a useful concept for planning trajectories, how perceivability can be determined using reachability analysis, and how a Control Barrier Function controller can be used to design controllers to maintain a desired level of information.

High actuation capability and smooth-deformation piezo morphing wing based on multi-layer parallel pre-compressed MFC bimorph

A single macro-fiber composite (MFC) unimorph or bimorph wing can only be applied to micro aerial vehicles (MAV) at speeds lower than 20 m/s owing to its relatively small output work. In this study, a high-actuation MFC pre-compressed bimorph actuator (MFC-PBA) multilayer parallel morphing wing is proposed for application in high-speed miniature unmanned aerial vehicles (mini-UAVs). The morphing wing adopts the proposed ribs with an arc groove and three parallel layers of MFC-PBAs to improve the output work and guarantee smooth morphing wing surface. The large deformation finite element (FE) models of a single MFC-PBA and its multilayer parallel morphing wing are established to evaluate the output deformation and output force. Subsequently, a prototype of the morphing wing is fabricated, and the actuation capabilities of the single MFC-PBAs and morphing wing are tested. The experimental and FE simulation results satisfactorily agree. The results show that at the peak driving voltage, with axial compression forces of 18 and 27 N applied to the side and middle MFC-PBAs, respectively, the deflection angle of the morphing wing reaches ±12°, which is twice that of the morphing wing without compression; and its blocking force is maintained at 1.682 N; thus, its output work has doubled. The multiphysics model of the proposed morphing wing under airflow is established to evaluate the deformation capability. The results show that the present morphing wing achieves a deflection of 5.04° on the side of the incoming flow direction, and a unit lift of 249.1 N/m at an air speed of 40 m/s and angle of attack of 15°. Consequently, the proposed morphing wing exhibits a high deformation capability. We expect the proposed morphing wing will be used for the flight control of mini-UAVs at higher speeds and larger sizes.

Recent Developments on Dielectric Barrier Discharge (DBD) Plasma Actuators for Icing Mitigation

Ice accretion is a common issue on aircraft flying in cold climate conditions. The ice accumulation on aircraft surfaces disturbs the adjacent airflow field, increases the drag, and significantly reduces the aircraft’s aerodynamic performance. It also increases the weight of the aircraft and causes the failure of critical components in some situations, leading to premature aerodynamic stall and loss of control and lift. With this in mind, several authors have begun to study the thermal effects of plasma actuators for icing control and mitigation, considering both aeronautical and wind energy applications. Although this is a recent topic, several studies have already been performed, and it is clear this topic has attracted the attention of several research groups. Considering the importance and potential of using dielectric barrier discharge (DBD) plasma actuators for ice mitigation, we aim to present in this paper the first review on this topic, summarizing all the information reported in the literature about three major subtopics: thermal effects induced by DBD plasma actuators, plasma actuators’ ability in deicing and ice formation prevention, and ice detection capability of DBD plasma actuators. An overview of the characteristics of these devices is performed and conclusions are drawn regarding recent developments in the application of plasma actuators for icing mitigation purposes.

Design space and manufacturing of programmable 4D printed continuous flax fibre polylactic acid composite hygromorphs

The work describes the exploration of the design space by fabrication, modelling and testing of bio-based and humidity-triggered 4D printed shape-changing biocomposites. The aim is to broaden the understanding of the control actuation via printing path tailoring and unlock new potential applications for biomaterials and autonomous actuator design. The composites are made with continuous flax yarns and polylactic acid matrix filaments and exhibit moisture-induced actuation. The actuation capability is first demonstrated by printing a calla lily flower-inspired configuration subjected to 98% relative humidity. This structure did not however achieve the anticlastic double curvature and large actuation targeted. To resolve these issues, cross-ply composite architectures with bent filaments deposited in one layer have then been developed. The amplitude for curvature control ranges obtained were 1.9*10−3mm−1 and 7.9*10−3mm−1 depending on the position on the specimen. Other cross-ply hygromorphs solutions are also proposed, with the orientation of their passive layers ([0°]2) tilted by α degrees (stacking sequence: [-α,α, 90°]). The largest actuation curvature was obtained when α=40°, which increased by 0.0072 mm−1 when compared to α = 0°. The hygromorphs presented in this work are modelled using in an in–house filament scale finite element model able to capture the complexity of the printed hygromorphs architectures.

Development of a novel parallel soft manipulator with sensing capabilities

It is challenging to equip a soft manipulator with sensors without compromising its mechanical properties. In this paper, we explain the design, analysis, and building of an innovative, low-cost soft parallel manipulator with sensing and actuation capabilities. Innovative bubble artificial muscle actuators serve as the connecting rod and contraction type actuator for the manipulator, as well as an opto-mechanical tactile sensor (TacTip) for objects detection. We propose a simulation method for the key structural design parameters of TacTip, and the influence of TacTip’s pin height, pin diameter, and surrounding pin angle on perceptual sensing has been examined via testing, which can provide a design guideline for the TacTip’s the structure. The impact of the counterweight on the soft parallel manipulator end-ascending effector’s and descending velocity, as well as its vertical and horizontal workspace, has been the topic of dynamic tests using a range of counterweights. The soft parallel manipulator’s workspace has been analyzed. In addition, an innovative, cost-effective, and simple soft-smart parallel robotic manipulator (PSM) control system has been built, and a demonstration of the detection and movement of the soft parallel manipulator is shown. The results demonstrate that the soft parallel manipulator described in this research is capable of detecting motion and collisions. It is anticipated that this soft-smart PSM would expand the employment of optical tactile sensors and artificial muscle actuators in material handling and size/shape sorting assembly lines.

Review on Research Progress of Hydraulic Powered Soft Actuators

Soft actuators have received extensive attention in robotics and smart device applications due to their distinctive dexterity and compliance. Among them, hydraulic soft actuators play an important role in the area because they have much higher specific power and power density than other types such as pneumatic soft actuators. Nevertheless, the deformation of flexible materials in soft actuators brings about inherent hysteresis and nonlinearity, which severely hinders them from producing the desired movement in the presence of advanced control strategies. In this paper, previous research efforts made to enhance the driving capability and actuation efficiency of hydraulic soft actuators are illustrated and analyzed from the three aspects of architecture, materials, and control strategy. Meanwhile, the issues and challenges that have emerged when developing hydraulic soft actuators are discussed. Finally, the potential future development of hydraulic powered soft actuators is discussed.

A pendulum actuator for environmental vibration isolation based on magnetostrictive composite material

In precision optical experiments, optical devices are usually suspended by pendulum systems to isolate environmental vibration. However, a traditional pendulum vibration isolator only isolates the horizontal vibration. Here, a new type of pendulum actuator, which bases on giant magnetostrictive composite material, is proposed to achieve environmental vibration isolation. The core element in actuator is a flexible wire, which is made of a thin quartz fiber embedded in epoxy resin-bonded magnetostrictive composite material with Terfenol-D particles. The designed flexible wire is deformable in vertical direction and capable to isolate the vertical vibration. The experiments are performed to verify the performance of the actuator. The response of the actuator shows great linearity with a sensitivity of 0.78 μm/A to the driving current. It also shows a large elongation range up to 5.9 μm in the linear area. Furthermore, performance of actuator on environmental vibration isolation is tested. The peak-to-peak value of vibration along vertical direction can be reduced by 17.5 dB with no negative impact on vibration along horizontal direction, which corroborates the capability of the novel pendulum actuator to isolate the environmental vibration in precision measurement.

Dynamic AIE crosslinks in liquid crystal networks: visualizing for actuation‐guiding, re‐bonding for actuation‐altering

AbstractCovalent adaptable liquid crystal networks (CALCNs) are highly potential actuating materials due to their actuation properties and shape reprogrammability. Given the importance of network crosslinking state in a CALCN actuator, we sought an all‐in‐one strategy to probe and visualize its dynamic network while ensuring actuation and reprogramming. Here, tetraphenylethylene derivatives were incorporated into liquid crystal networks via the Diels–Alder (DA) reaction, acting simultaneously as reversible crosslinkers and aggregation‐induced emission (AIE) fluorescent probes. The thermally tunable fluorescence of the resulting network can correlate to and thus visualize the actuator's crosslinking status, actuation capability and temperature in real‐time and in situ, yielding an intriguing actuation limit‐alerting function. Furthermore, we verified unprecedented reprogrammability of the AIE‐type CALCNs through both associative and dissociative exchange mechanisms of DA chemistry.

Dynamic AIE crosslinks in liquid crystal networks: visualizing for actuation-guiding, re-bonding for actuation-altering.

Covalent adaptable liquid crystal networks (CALCNs) are highly potential actuating materials due to their actuation properties and shape reprogrammability. Given the importance of network crosslinking state in a CALCN actuator, we sought an all-in-one strategy to probe and visualize its dynamic network while ensuring actuation and reprogramming. Here, tetraphenylethylene derivatives were incorporated into liquid crystal networks via the Diels-Alder (DA) reaction, acting simultaneously as reversible crosslinkers and aggregation-induced emission (AIE) fluorescent probes. The thermally tunable fluorescence of the resulting network can correlate to and thus visualize the actuator's crosslinking status, actuation capability and temperature in real-time and in situ, yielding an intriguing actuation limit-alerting function. Furthermore, we verified unprecedented reprogrammability of the AIE-type CALCNs through both associative and dissociative exchange mechanisms of DA chemistry.

Magnetorheological Fluid-Based Bending Actuator for Magnetic Sensing

Magnetorheological (MR) fluids have applications in diverse areas such as automobile suspension, architecture, and vibration control due to their fast response, wide range of controllability, and temperature resistance. However, traditional MR fluids-based applications for robotics lack the capability of sensing that can provide information about the environment. In this letter, we present a MR fluid-based bending actuator for magnetic sensing by integrating a strain gage into the actuator. Its deflection can be detected by reading the change of resistance when the actuator deflects under different external magnetic fields. Subsequently, we obtain the relationship between the magnetic flux density and the deflection by deriving an analytical model. To demonstrate the magnetic actuation capability of the actuator, we fabricate a fish-like robot whose tail is composed of the actuator. We further conduct simulations and experiments to validate the analytical model of magnetic sensing. This model shows good agreement with the simulation and experiment results. We validate the actuator for magnetic sensing by demonstrating that it can exhibit a good tracking response of dynamic signals (maximum absolute error smaller than 2.5 mT). The results illustrate that the MR fluid-based bending actuator has the potential to use in the environmental inspection.

Manufacturing smart surfaces with embedded sensors via magnetron sputtering and laser scribing

Magnetron Sputtering (MS) together with patterning via Laser Scribing allows manufacturing of thin film sensors/actuators embedded on the surface of components. These transducers add active monitoring and/or actuation capabilities to the piece, hence they are termed smart surfaces. To embed the sensors/actuators, the target surface is coated by MS with a 2 – 3 µm insulator layer (usually a metal oxide such as SiO2, Si3N4 or Al2O3), and afterwards with a 0.5 – 2.0 µm metallic conductor layer. Alternatively, a 15 µm dielectric lacquer deposited by spray coating is used as the insulator layer. The conductor is then selectively removed by LS without removing the insulator to draw a circuit completely isolated from the piece. The scribing of the circuits is done with a femtosecond laser (λ = 517 nm) that allows extremely quick (∼200 mm/s) and accurate manufacturing of a sensor in a few seconds with ∼30 µm space resolution. The type of sensor is determined by the selection of the conductor(s) and insulator(s) materials and the shape of the circuit, and can be manufactured to match the specifications of the application by modifying the MS and LS parameters. In this work two types of embedded sensors were manufactured and tested: Resistive temperature detectors made of Al, Ti, W or Cu, and strain gauges made of NiCr. These embedded sensors can measure with a high degree of precision as they are directly connected with the piece without adhesives or polymer foils, and even without humidity, organics, or oxygen in between. In addition, this technology allows lo locate sensors in components with complex geometries, in places difficult to access with a traditional sensor, and as the sputtered sensors are only a few micrometres-thick they do not affect the dimensional tolerance of the piece.

Chemical sensing and actuation properties of polypyrrole coated fibers

Designing complex electrochemical artificial muscles aims towards novel devices which besides excellent actuation capabilities should also present the ability to self-sense the modification of environmental parameters. In order to improve efficiency, mimicking the structure of natural muscles, synthetic actuators should have a similar fibrillary morphology. The importance of using materials based on fiber building blocks in actuators aimed at soft robotics field was demonstrated in the present report by comparing a fibrillary artificial muscle with one based on a classical film structure. Nylon electrospun fiber meshes and films were covered in the same conditions with a thin polypyrrole (PPy) layer. The fibrillary electrospun web morphology mimics that of natural muscles and the structure performs a fast, ample bending movement in liquid electrolyte when switching an applied electric potential between −0.6 and +0.6 V. Using the same actuation conditions, no movement of a film based artificial muscle was observed. In order to check the sensing ability of both fibrillary and film like electroactive architectures, their response i.e. PPy reaction when potential cycles were applied in different concentrations of LiClO4 electrolyte were recorded. The obtained results suggest that the ion exchange of the fibrillary artificial muscle is more efficient due to its higher active surface and such devices could work also as dual device (sensor/artificial muscle).

Bionic design and performance research of tracheal stent based on shape memory polycaprolactone

Trachea injury caused by tracheomalacia, stenosis or atresia can result in severe dyspnea, even asphyxia. With the development of trachea reconstruction technology, trachea stents have become an alternative treatment method. Here, we fabricated a kind of shape memory PCL/Fe3O4 composites (SMPC-PCL) by mixing different weight fractions of benzoyl peroxide and Fe3O4 nanoparticles. The addition of magnetic nanoparticles endowed SMPC-PCL with the capability of remote non-contact actuation, which exhibited unique advantages in minimally invasive implantation and adaptive ability. Further, based on fully observing the unique reticular structure of glass sponges, two types of biomimetics stents were designed and fabricated, and the mechanical properties were thoroughly investigated by experiments and finite element analysis. The minimally invasive implant performance and biological characterization were carried out to evaluate its availability. The excellent mechanical properties, minimally invasive implant performance and biological properties suggest the application potential in tracheal stents.

4D Printing of Freestanding Liquid Crystal Elastomers via Hybrid Additive Manufacturing.

Liquid crystal elastomers (LCE) are appealing candidates among active materials for 4D printing, due to their reversible, programmable and rapid actuation capabilities. Recent progress has been made on direct ink writing (DIW) or Digital Light Processing (DLP) to print LCEs with certain actuation. However, it remains a challenge to achieve complicated structures, such as spatial lattices with large actuation, due to the limitation of printing LCEs on the build platform or the previous layer. Herein, a novel method to 4D print freestanding LCEs on-the-fly by using laser-assisted DIW with an actuation strain up to -40% is proposed. This process is further hybridized with the DLP method for optional structural or removable supports to create active 3D architectures in a one-step additive process. Various objects, including hybrid active lattices, active tensegrity, an actuator with tunable stability, and 3D spatial LCE lattices, can be additively fabricated. The combination of DIW-printed functionally freestanding LCEs with the DLP-printed supporting structures thus provides new design freedom and fabrication capability for applications including soft robotics, smart structures, active metamaterials, and smart wearable devices.