Actuation Capabilities Research Articles

Heat-stimuli controllability of shape memory thermoplastic epoxy filaments by adding polyethylene glycol

This study prepared shape-memory thermoplastic epoxy (TEP)-polyethylene glycol (PEG) filaments for the first time, and the heat-stimuli controllability of shape memory function was innovatively endowed by adding PEG in an environmentally friendly way. PEG regulates the glass transition temperature of PEG-modified thermoplastic epoxy (TEP–PEG) without interfering with the polymerization reaction of epoxy. The melt spinning temperature of TEP–PEG is also reduced from 300 °C to 220 °C, and the spinning effect is improved. After PEG modification, Young's modulus of TEP–PEG filaments drawn from TEP–PEG pellets was higher at room temperature. The developed TEP–PEG filaments have excellent shape memory effect with high shape recovery rates of 93.1%–99.0%, and shape fixation rates ranging from 95.8% to 99.1% are also improved after PEG modification. Furthermore, TEP–PEG filaments have controllable stimuli temperatures of shape memory ranging from 69 °C to 105 °C. Additionally, the recovery stress of TEP–PEG filaments after PEG modification was increased to 1.77 MPa, and the recovery temperature of the maximum recovery stress is reduced from 97 °C to 58 °C as PEG content increases to 15 wt%. The problems of difficult melt processing and uncontrollable stimuli temperature for TEP were solved in this study. The developed TEP-PEG filaments with heat-stimuli controllability of the shape memory function demonstrated excellent thermal actuation capabilities and have shown greater application potential in thermal actuation, smart textiles, and artificial muscles.

Dual driven mechanism (hygro‐redox) semi‐interpenetrating polymer network composite film (polyaniline‐polyacrylic acid/sulfonated poly (ether ether ketone)) for artificial muscles

AbstractDifferent weight ratios of polyaniline (PANI) to poly (acrylic acid) (PAA) were synthesized as interpenetrating polymer networks and blended with sulfonated poly (ether ether ketone) (SPEEK). In‐situ polymerization was performed by chemical oxidation of aniline in the presence of PAA. The composites showed actuation capability in the presence of fuel/air and moisture. Mechanical testing indicated that samples with higher concentration of PAA were stronger. For instance, PANI1PAA2SPEEK3 breaks at 8.4 MPa and has a failure strain of 2.5%, which is higher than PANI3PAA1SPEEK3 at 7 MPa and 2%. However, higher amount of PAA resulted in a lower electrochemical conductivity of 1.52 × 10−2 S/cm for the former and 1.8 × 10−2 S/cm for the latter. Intermolecular interaction at the optimum composition is necessary to induce forward and reverse bending of catalyst coated composite under exposure of fuel and air. In addition, the formation of compact structures and rough surfaces resulted in the maximal contractile strain of 1% for PANI3PAA1SPEEK3 based on moisture actuation.

Bioinspired Structures for Soft Actuators

AbstractBiological organisms present marvelous morphing behaviors from the quiescent blooming of flowers to the energetic wing‐flapping of birds that have always inspired humans to design better‐engineered products. The diversity of natural motion is attributed primarily to the intricate and hierarchical structure of actuators that are self‐assembled from nanoscale structures to superstructures. Compared to the biological actuators, their manmade counterparts, often with significantly limited capabilities, are fabricated from various materials with relatively simple structures using limited fabrication techniques. With the rapid developments in technologies that require soft robotics and human‐machine interfaces, there is increasing demand for soft actuators with improved capabilities such as larger output force, repeatability, and a more comprehensive range of motion. Biological actuators provide critical insights into the structure‐function relationship and offer exciting concepts to advance the science and technology of artificial soft actuators. Here, the design approaches found in natural actuation systems are discussed from the nanoscale to the highest levels in the structural hierarchy and the physical principles involved in their diverse actuation capabilities. In that context, finally, the fabrication techniques that have been utilized for manmade soft actuators, with a focus on the advantages, challenges, and concepts for potential future developments are reviewed.

Parametric instability in the neutron star extreme matter observatory

Parametric instability (PI), induced by the interaction between the cavity optical modes and acoustic modes of a mirror, is an inherent risk in interferometric gravitational wave detectors. The instability can result in exponential growth in acoustic mode amplitude and the saturation of detectors control systems. In this paper we analyse PI in the neutron star extreme matter observatory, a proposed high optical power (4.5 MW) detector, operating at cryogenic temperatures with silicon test masses (TMs), targeting high sensitivity between 1 and 4 kHz. Our results show that with current design parameters, approximately 16 unstable modes will arise per TM with maximum parametric gain ∼10. Varying the TM radius of curvature from the nominal values could eliminate PI, however not with current manufacture or actuator capability. PI mitigation will be required to suppress all unstable modes. This analysis identifies four optical modes and 16 acoustic modes dominating PI in NEMO paves the way for the design of PI mitigation strategies.

Simultaneous tip force and displacement sensing for AFM cantilevers with on-chip actuation: Design and characterization for off-resonance tapping mode

The use of integrated on-chip actuation simplifies the identification of a cantilever resonance, can improve imaging speed, and enables the use of smaller cantilevers, which is required for low-force imaging at high speed. This article describes a cantilever with on-chip actuation and novel dual-sensing capabilities for AFM. The dual-sensing configuration allows for tip displacement and tip force to be measured simultaneously. A mathematical model is developed and validated with finite element analysis. A physical prototype is presented, and its calibration and validation are presented. The cantilever is optimized for use in off-resonance tapping modes. Experimental results demonstrate an agreement between the on-chip sensors and external force and displacement measurements.

A soft syntactic foam actuator with high recovery stress, actuation strain, and energy output

Novel syntactic foams were prepared by incorporating three types of glass microbubbles in a crosslinked cis poly(1,4-butadiene) (cPBD) matrix. The as-prepared semi-crystalline polymer-based syntactic foams displayed a clear two-way shape memory effect (2W-SME) with remarkable strain actuation of about 56% expansion when the temperature drops from 60 °C to − 40 °C, and about 40% contraction when the temperature rises from − 40 °C to 60 °C, comparable to most pure two-way shape memory polymers. Compared to the pure cPBD, which was actuated under 0.32 MPa tensile stress, the foams were actuated under a much larger external tensile stress of up to 1.6 MPa, signifying its superior actuation capability. The energy output is also much higher for the syntactic foam, up to 0.83 MJ/m3, compared to 0.28 MJ/m3 for the pure cPBD. Furthermore, it has a working temperature below zero Celsius and may be actuated at temperatures lower than most other available shape memory polymer foams. With a low density, decent mechanical properties, and great actuation capability, these syntactic foams can be adopted for applications such as artificial muscles, biomedical devices, soft robots, sealants, and aerospace structures, which can be potentially manufactured by 3D printing.

Finite-horizon, energy-efficient trajectories in unsteady flows.

Intelligent mobile sensors, such as uninhabited aerial or underwater vehicles, are becoming prevalent in environmental sensing and monitoring applications. These active sensing platforms operate in unsteady fluid flows, including windy urban environments, hurricanes and ocean currents. Often constrained in their actuation capabilities, the dynamics of these mobile sensors depend strongly on the background flow, making their deployment and control particularly challenging. Therefore, efficient trajectory planning with partial knowledge about the background flow is essential for teams of mobile sensors to adaptively sense and monitor their environments. In this work, we investigate the use of finite-horizon model predictive control (MPC) for the energy-efficient trajectory planning of an active mobile sensor in an unsteady fluid flow field. We uncover connections between trajectories optimized over a finite-time horizon and finite-time Lyapunov exponents of the background flow, confirming that energy-efficient trajectories exploit invariant coherent structures in the flow. We demonstrate our findings on the unsteady double gyre vector field, which is a canonical model for chaotic mixing in the ocean. We present an exhaustive search through critical MPC parameters including the prediction horizon, maximum sensor actuation, and relative penalty on the accumulated state error and actuation effort. We find that even relatively short prediction horizons can often yield energy-efficient trajectories. We also explore these connections on a three-dimensional flow and ocean flow data from the Gulf of Mexico. These results are promising for the adaptive planning of energy-efficient trajectories for swarms of mobile sensors in distributed sensing and monitoring.

A modern Blackboard Architecture implementation with external command execution capability

A modern implementation of a simplified version of the Blackboard Architecture is presented herein. It uses a rule-fact-action network and a round-robin rule processing engine. It also includes external command actuation capabilities for action nodes, making it highly extensible. The implementation is modular so components (such as the rule processing engine) could be readily replaced, if desired, while utilizing other system functionality. The implementation features a command processor interface, allowing systems to be implemented without the need to write any procedural code. The network can be developed and run using the simplified command processor language created especially for this use.

Magnetic Miniature Actuators with Six‐Degrees‐of‐Freedom Multimodal Soft‐Bodied Locomotion

Magnetic miniature robots (MMRs) are mobile actuators that can exploit their size to noninvasively access highly confined, enclosed spaces. By leveraging on such unique abilities, MMRs have great prospects to transform robotics, biomedicine, and materials science. As having high dexterity is critical for MMRs to enable their targeted applications, existing MMRs have developed numerous soft‐bodied gaits to locomote in various environments. However, there exist two critical limitations that have severely restricted their dexterity: 1) MMRs capable of multimodal soft‐bodied locomotion have only demonstrated five‐degrees‐of‐freedom (five‐DOF) motions because the sixth‐DOF rotation about their net magnetic moment axis is uncontrollable; 2) six‐DOF MMRs have only realized one mode of soft‐bodied, swimming locomotion. Herein, a six‐DOF MMR is proposed that can execute seven modes of soft‐bodied locomotion and perform 3D pick‐and‐place operations. By optimizing its harmonic magnetization profile, the MMR can produce 1.41–63.9‐fold larger sixth‐DOF torque than existing MMRs with similar profiles, without compromising their traditional five‐DOF actuation capabilities. The proposed MMR demonstrates unprecedented dexterity: it can jump through narrow slots to reach higher grounds; use precise orientation control to roll, two‐anchor crawl, and swim across tight openings with strict shape constraints; and perform undulating crawling across three different planes in convoluted channels. An interactive preprint version of the article can be found at: https://www.authorea.com/doi/full/10.22541/au.164087652.25227465.

Effects of Inflation Pressure and Wall Thickness on Gripping Force of Semi-Cylindrical Shaped Soft Actuator: Numerical Investigation

Soft robotics using Pneumatic Network actuators (Pneu-Net) is a developing field that has a promising future for variety of applications involving delicate operations such as biomedical assistance. The interaction between geometry and the performance of the actuator is an important topic which has been studied by many researchers in this field. However, there is a lack of investigation on the relationship between gripping capability and geometrical parameters of soft actuators. Especially, there is a need to shed more light on the effects of wall thicknesses on the gripping force developed. In the present study, a semi-cylindrical chambered PneuNet soft actuator is numerically investigated to evaluate the effects of pressure and wall thickness variations on its performance characteristics. The results revealed that increasing the restraining layer thickness (RLT) aids the bending capability of the actuator whereas increasing the chamber wall thickness reduces it. Therefore, maximum bending of the actuator is achieved at the combinations of minimum wall thickness and maximum RLT. At these geometrical configurations of maximum bending, the deformation-pressure relationships followed a sigmoidal function and tended towards linearity with increasing wall thickness and decreasing RLT. The gripping force showed an exponential increase with increasing working pressures and wall thicknesses. The maximum gripping force increased cubically with increasing wall thicknesses at their respective maximum working pressures, which was modeled using a polynomial regression model (R2=99.79%).

High-Power Shape Memory Alloy Catapult Actuator for High-Speed and High-Force Applications

Nickel-Titanium (NiTi) based shape memory alloy (SMA) wires are already often used in industrial actuator applications. Their high energy density allows to build light-weight actuator systems with high forces using small installation spaces. Combined with the biocompatibility of NiTi, a huge field of applications can be covered by SMA actuated systems. In systems like emergency brakes or switch disconnectors, which require high forces as well as high actuation speed, the high-power capability of NiTi actuators is exploited. The presented work details the development and characterization of a giant power catapult demonstrator, that combines the high-speed and high-force capability of SMA wires. To illustrate the vast force, speed, and power potential of SMA wires, a bowling ball is launched from its resting position vertically into the air using SMA wires. For demonstration purposes a target altitude for the bowling ball of 500 mm is chosen. With the height and the overall accelerated mass given, an actuation force <i>F</i> &#x2245; 920 N is needed. The instantaneous energy release from the designed power source results in the targeted flight height and an overall peak power of <i>P</i> &#x2245; 0.5 MW.

Сегнетоэлектрические полимеры с улучшенными характеристиками

This article offers a short overview of the unique properties of PVDF-based electroactive polymers and their applications. Ferroelectric materials are widely used in modern electronics. Relaxor-ferroelectric terpolymers are multifunctional materials with high electrostrictive strain which, in turn, leads to large actuation capability. The terpolymer with clorofluoroethylene shows relaxor-ferroelectric behavior with vanishing hysteresis effect but considerably higher polarization. Therefore, such material is a potential candidate for energy-storage devices (supercapacitors).

Inequality Constrained Optimal Control for Rope-Assisted ASV Docking Maneuvers

In difficult whether conditions the complexity of docking maneuvers of autonomous surface vessels (ASVs) increases. Docking maneuvers take place in proximity to piers and other vessels. The slow speed at which the maneuvers take place decreases the maneuverability of the vessel and environmental disturbances such as wind and waves increase in effect. In these scenarios ropes can be utilized to support the maneuver and compensate for the compromised actuation capabilities. The modeling of the modified mechanics plays a center role. It has been shown in previous work that this setup, connecting the vessel to the pier with a constant distance (e.g. with a rod) can be modeled using the concept of differential-algebraic equations (DAEs). With the adapted vessel dynamics a trajectory generation problem can be solved using optimal control theory. Here, a direct numerical method, in this case a full discretization of the optimal control problem (OCP), is used. The contribution in this paper allows for slackness in the rope. This is done by using a smooth penalty function, as well as solving a complementary problem. Both methods lead to feasible solutions. The penalty function shows are more smooth behavior but suffers from numerical robustness in comparison to the linear complementary solution.

Optimizing the Sensory Apparatus of Voxel-Based Soft Robots Through Evolution and Babbling

The behavior of biological and artificial agents strongly depends, in general, on the data acquired through sensors while interacting with the environment. The sensory apparatus, namely the location and kind of sensors, has therefore a great impact on an agent’s ability of exhibiting complex behaviors. Considering the case of robots, sensors are usually a design choice that is hard to take, due to the complexity of the robotic structure and a potentially large number of possible combinations. Here, we explore the possibility of using evolutionary algorithms to automatically design (and optimizing their use) the sensors of voxel-based soft robots (VSRs), a kind of robots composed of multiple deformable components. We chose these robots due to their intrinsic modularity, which allows to freely shape the robot body, brain, and sensory apparatus. We consider a set of sensors that allow agents to sense themselves and their environment and we show, experimentally, that the effectiveness of the sensory apparatus depends on the body shape and the actuation capability. Then, we show that evolutionary optimization is able to evolve effective sensory apparatuses, even with constraints on the availability of sensors. We also consider how information from sensors can be exploited more efficiently by introducing the concept of “sensor babbling”, which aims to enhance the robots’ perception and, hence, their performances.

A Sea-Anemone-Inspired, Multifunctional, Bistable Gripper.

The growing need for soft robots with secure, adaptive, and autonomous functioning in unforeseen environments favors designs with multiple functionalities. This has driven soft robotic grippers to be explored to integrate perceptual capability for augmented multifunctionality. In nature, sea anemones can detect and catch preys of various shapes and sizes effectively with extremely simple bodies because of the efficient coupling of sensing and actuation capability. Inspired by their body structures, we present a bistable gripper with multifunctionality that includes sensing (proprioceptive and exteroceptive) and multimodal gripping (grasping and pinching). The gripper exploits an array of tapered pins on the external surface of a dome membrane for gripping and a set of cylindrical markers on the internal surface of the membrane for optical sensing. The membrane is bistable and can settle in either of two equilibrium states "natural" and "retracted." Gripping functionality is achieved by the centripetal enveloping movement of the pins, along with the passive snap-through process of the membrane. By analyzing the distribution of markers within the view of an embedded camera, sophisticated sensing functionality can be achieved. We first characterized each function separately and then implemented an object handling system, combining the sensing and gripping functionality, to demonstrate the potential for more advanced robotic applications. This work delivers a compact universal gripper design with an efficient and elegant integration of multifunctionality.

Ethanol Phase Change Actuator Based on Thermally Conductive Material for Fast Cycle Actuation.

Artificial muscle actuator has been devoted to replicate the function of biological muscles, playing an important part of an emerging field at inter-section of bionic, mechanical, and material disciplines. Most of these artificial muscles possess their own unique functionality and irreplaceability, but also have some disadvantages and shortcomings. Among those, phase change type artificial muscles gain particular attentions, owing to the merits of easy processing, convenient controlling, non-toxic and fast-response. Herein, we prepared a silicon/ethanol/(graphene oxide/gold nanoparticles) composite elastic actuator for soft actuation. The functional properties are discussed in terms of microstructure, mechanical properties, thermal imaging and mechanical actuation characteristics, respectively. The added graphene oxide and Au nanoparticles can effectively accelerate the heating rate of material and improve its mechanical properties, thus increasing the vaporization rate of ethanol, which helps to accelerate the deformation rate and enhance the actuation capability. As part of the study, we also tested the performance of composite elastomers containing different concentrations of graphene oxide to identify GO-15 (15 mg of graphene oxide per 7.2 mL of material) flexible actuators as the best composition with a driving force up to 1.68 N.

Smart actuation of liquid crystal elastomer elements: cross-link density-controlled response

Liquid crystal elastomers (LCEs) exhibit some remarkable physical properties, such as the reversible large mechanical deformation induced by proper environmental stimuli of different nature, such as the thermal stimulus, allowing their use as soft actuators. The unique features displayed by LCE are originated from their anisotropic microstructure characterized by the preferential orientation of the mesogen molecules embedded in the polymer network. An open issue in the design of LCEs is how to control their actuation effectiveness: the amount of mesogens molecules, how they are linked to the network, the nematic order degree, the cross-link density are some controllable parameters whose spatial distribution, in general, cannot be tuned except for the last one. In this paper, we develop a theoretical micromechanical-based framework to model and explore the effect of the network cross-link density on the mechanical actuation of LCE elements. In this context, the light-induced polymerization (photopolymerization) for obtaining the elastomers’ cross-linked network is of particular interest, being suitable for precisely tuning the cross-link density distribution within the material. This technology enables to obtain a molecular-scale architected LCEs, allowing the optimal design of the obtainable actuation. The possibility to properly set the cross-link density arrangement within the smart structural element (LCE microstructure design and optimization), represents an intriguing way to create molecular-scale engineered LCE elements having a material microstructure encoding the desired actuation capabilities.

4D-actuators by 3D-printing combined with water-based curing

The shape and the actuation capability of state of the art robotic devices typically relies on multimaterial systems from a combination of geometry determining materials and actuation components. Here, we present multifunctional 4D-actuators processable by 3D-printing, in which the actuator functionality is integrated into the shaped body. The materials are based on crosslinked poly(carbonate-urea-urethane) networks (PCUU), synthesized in an integrated process, applying reactive extrusion and subsequent water-based curing. Actuation capability could be added to the PCUU, prepared from aliphatic oligocarbonate diol, isophorone diisocyanate (IPDI) and water, in a thermomechanical programming process. When programmed with a strain of εprog= 1400% the PCUU networks exhibited actuation apparent by reversible elongation ε'rev of up to 22%. In a gripper a reversible bending ε'rev(bend) in the range of 37–60% was achieved when the actuation temperature (Thigh) was varied between 45 °C and 49 °C. The integration of actuation and shape formation could be impressively demonstrated in two PCUU-based reversible fastening systems, which were able to hold weights of up to 1.1 kg. In this way, the multifunctional materials are interesting candidate materials for robotic applications where a freedom in shape design and actuation is required as well as for sustainable fastening systems.

A Soft Pneumatic Two-Degree-of-Freedom Actuator for Endoscopy.

The rise of soft robotics opens new opportunities in endoscopy and minimally invasive surgery. Pneumatic catheters offer a promising alternative to conventional steerable catheters for safe navigation through the natural pathways without tissue injury. In this work, we present an optimized 6 mm diameter two-degree-of-freedom pneumatic actuator, able to bend in every direction and incorporating a 1 mm working channel. A versatile vacuum centrifugal overmolding method capable of producing small geometries with a variety of silicones is described, and meter-long actuators are extruded industrially. An improved method for fiber reinforcement is also presented. The actuator achieves bending more than 180° and curvatures of up to 0.1 mm−1. The exerted force remains below 100 mN, and with no rigid parts in the design, it limits the risks of damage on surrounding tissues. The response time of the actuator is below 300 ms and therefore not limited for medical applications. The working space and multi-channel actuation are also experimentally characterized. The focus is on the study of the influence of material stiffness on mechanical performances. As a rule, the softer the material, the better the energy conversion, and the stiffer the material, the larger the force developed at a given curvature. Based on the actuator, a 90 cm long steerable catheter demonstrator carrying an optical fiber is developed, and its potential for endoscopy is demonstrated in a bronchial tree phantom. In conclusion, this work contributes to the development of a toolbox of soft robotic solutions for MIS and endoscopic applications, by validating and characterizing a promising design, describing versatile and scalable fabrication methods, allowing for a better understanding of the influence of material stiffness on the actuator capabilities, and demonstrating the usability of the solution in a potential use-case.

An enhanced flexoelectric dielectric elastomer actuator with stretchable electret

Actuation has been applied with dielectric elastomers (DE) in soft robotics and bio-mimic devices due to their ultra-large deformation range, easy patterning, light weight, and they are highly expected for high electro-mechanical efficiency and low stimulating power. Flexoelectricity describes the strain gradient-induced electric polarization, which is strongly related to geometry and deformation ranges. The electro-mechanical coupling effect with flexoelectricity in elastomeric materials are then highly expected. In this work, elastic modulus gradient of a DE actuator is designed for bending motion by flexoelectricity, and electric charge is inserted and immobilized inside the material to further enhance the electro-mechanical capability. Elastic modulus gradient is designed, and electric charges are immobilized to enlarge the electro-mechanical coupling efficiencies of this flexoelectric actuator. The bending angle of the actuator is inversely proportional to the cube of general thickness of actuator, and the immobilized electric charge extensively enlarged the actuation capability. With elastic modulus gradient and electret, the actuating bending angle is enlarged with low stimulating voltage. This work provides an enhanced flexoelectric actuating method with material and mechanical design, and highlights low-voltage actuating approach with piezoelectric-like effect of stretchable electrets.