Smart Actuators Research Articles

Hysteresis online identification approach for smart material actuators with different input signals and external disturbances

Hysteresis online identification approach for smart material actuators with different input signals and external disturbances

Programmable Mechanical Metamaterials with Tailorable Negative Poisson's Ratio and Arbitrary Thermal Expansion in Multiple Thermal Deformation Modes.

Mechanical metamaterials pave a way for designing and optimizing microstructure topology to achieve counterintuitive deformation including negative Poisson's ratio (NPR) and negative thermal expansion (NTE). Previous studies were always limited to single anomalous mechanical or thermal deformation, but current applications for high-precision mechanical or optical equipment always require their combination and customized and anisotropic deformation parameters. This work develops programmable two-dimensional (2D) mechanical metamaterials based on chiral and antichiral structures constructed with curved bimaterial strips to produce tailorable NPR and arbitrary thermal deformation. The coefficient of thermal expansion of the mechanical metamaterials is tunable on a large scale across negative, near-zero, and positive values depending on the bimaterial configurations and geometrical parameters of curved strips, while the value of NPR is mainly determined by the radian. Furthermore, it is programmable by coding the unit cells to exhibit customized and anisotropic thermal deformation combining homogeneous, gradient, and shear modes. The proposed mechanical metamaterials are fabricated by multimaterial three-dimensional (3D) printing, and the unusual deformation modes are verified experimentally, which is well in agreement with the results of finite element analysis. This work demonstrates a feasible approach to achieving customized mechanical and thermal deformation through easy block building for specific engineering applications including eliminating thermal stress, shape morphing, and smart actuators.

A novel nature-inspired anisotropic hydrogel with programmable shape deformations

Stimulus-responsive anisotropic hydrogels have attracted tremendous attention in the fields of actuators, soft robots, and artificial muscles due to their ability to perform complex programmable motions. However, it is still challenging to construct anisotropic hydrogels via a simple way without the assistance of external fields. Inspired by gradient dissolved oxygen in seawater, we proposed a novel simple structure programming strategy to prepare anisotropic hydrogels using low-cost natural oxygen as the driving force. Encouragingly, this strategy, which relied on the asymmetric inhibitory behavior of natural gradient dissolved oxygen toward radical polymerization and electrostatic attraction between polyelectrolyte chains, enabled the obtained anisotropic hydrogels with both gradient structure and phase-separated structure. It is found that this complex asymmetric structure allowed anisotropic hydrogels be capable of complex deformations under different environmental conditions (temperature, pH), such as blooming and wilting flower shapes. Additionally, a humidity alarm and a four-armed hydrogel gripper were successfully constructed based on the designed anisotropic hydrogel, which indicated that our work provides a new strategy for the field of smart actuator fabrication.

Network of selectively compliant actuators based on shape memory alloys and polymers for a reconfigurable sandwich panel

Shape memory alloys (SMA) allow for the realization of smart actuators capable of achieving large stresses and large strains but highly demanding in terms of power input. This work presents a solution integrating shape memory polymers (SMP) in a novel type of selectively compliant actuator to reduce the power input of SMAs. The thermally induced variation in stiffness of the SMP is used to achieve large deformations by temporarily increasing the compliance of the actuator and to lock the actuator in a deformed state by restoring the initial stiffness. The behavior of the actuator is simulated taking into account the viscoelastic behavior of the SMP and validated through a comparison with experimental results. The latter show that the proposed actuator can achieve a maximum contraction of 3.0% and hold a contraction of about 1.6% multiple times without constantly powering the SMA. Finally, a reconfigurable sandwich panel is considered as possible application. A distributed actuator network is implemented in the face sheets of the panel and a digital image correlation system is used to prove the capability of the proposed structure of undergoing large deformations, holding a deformed shape without consuming energy, and recovering its initial shape. A further development of this panel might find application as support structure for morphing aerodynamic surfaces or reconfigurable antennas.

Hydrophilic/Hydrophobic SiO2 Nanoparticles Enabled Janus‐Type Paper through Commercial Glaco Spraying and Air‐Plasma Treatment

AbstractFunctional paper‐based microdevices have been receiving wide attention in the research areas of microfluidic chips, soft actuators, etc. This work introduces the design and fabrication of a Janus‐type paper in which one side of the paper remains hydrophilic and the other side is hydrophobic. Such Janus‐type paper is prepared by directly spraying hydrophobic Glaco solutions and following air plasma treatment. The former treatment can cover the paper fibers with numerous hydrophobic SiO2 nanoparticles. Through optimizing the fabrication parameters of the air plasma, it can penetrate the filter paper in a controllable depth, resulting in effectively regulating the hydrophobic particles into hydrophilic ones. Thereafter, the antirotation and interfacial stability of the Janus paper are investigated. Finally, a liquid storage and contamination‐free analysis devices are demonstrated on the Janus‐type paper platform. Noting that the commercially nonfluoride coating (Glaco) and mature plasma instrument together make the fabrication method simple, rapid, users/environmental‐friendly, and mass‐produced. The method provides a new route to fabricate Janus‐type paper for potential multifunctional applications in microfluidic chips and smart actuators, and may open up new avenue to prepare Janus films in a simple/rapid way.

3D Printing of Robotic Soft Grippers: Toward Smart Actuation and Sensing

AbstractUnlike traditional hard grippers, soft robotic grippers are commonly made of soft materials so that the soft grippers can produce motion via elastic deformations of their compliant components. The advantages of compliance allow soft grippers to effectively eliminate shocks caused by hard contact, which usually occurs when a hard robotic gripper manipulates a hard object. Until now, the soft robotic grippers are able to operate numerous objects with irregular geometries and different textures. Besides, with the help of embedded sensors, soft robotic grippers have facilitated the growing automation of many tasks, which are thought to be far too delicate for robotic manipulation. This paper reviews the advancement in soft robotic grippers. The paper first introduces the actuation technologies followed by the design and fabrication techniques. The use of 3D printing techniques in the fabrication of the soft gripper is also discussed. The Review then highlights the challenges and future outlook in the fabrication of soft grippers and sensors.

Laser powder bed fusion of diatom frustule inspired bionic NiTi lattice structures: compressive behavior and shape memory effect

This work aimed to propose a feasible lattice structure to fully exploit the advantages of NiTi shape memory alloy, providing more options for the development of functional components such as micro-vibration isolators and smart actuators in the aerospace field. Inspired from the Campylodiscus diatom frustule, the novel NiTi-based truss lattice structures were designed and fabricated by laser powder bed fusion. Four lattice structures with different ratios of traditional sharp angle (TSA) number to bionic arc angle (BAA) number (ξ TSA/BAA) were designed and the effect of the ξ TSA/BAA on the compressive behaviors and shape memory effect (SME) was experimentally investigated and the failure mechanism was revealed using finite element (FE) simulation. Results showed that all components possessed a nearly dense microstructure (>98%) and high dimensional accuracy (size error < 2.5%). As the ratio of the number of TSA to BAA decreased, the maximum first peak force decreased by 31.5%, and the elastic modulus Eϵ =0.2% decreased from 1.81 GPa to 1.19 GPa. And the failure modes changed from layer-by-layer failure to shear failure. The simulation results were in agreement with the experimental results and revealed that the ξ TSA/BAA affected the compressive behaviors by controlling the stress value and distribution of components. Results of SME tests showed that the introduction of BAA design can improve the recovery performance, and the ξ 0/6 component exhibited the largest recoverable ratio and the lowest accumulated residual strain.

Programmable shape deformation actuated bilayer hydrogel based on mixed metal ions

The intelligent hydrogel actuators that respond to temperature have great application prospects in many fields. At the same time, the intelligent hydrogel actuators still have challenges in driving force, deformation intensity, and programming deformation. Herein, we fabricated a bilayer hydrogel actuator using a two-step photopolymerization method, which consists of a poly(N-isopropylacrylamide)-chitosan-N-2-hydroxypropyl trimethylammonium chloride (PNIPAm-HACC) layer with an LCST-type volume phase change and an alginate-polyacrylamide (SA-PAm) layer. We employed mixed metal ions (trivalent/divalent cations) to cross-link alginate-based hydrogels to construct two-dimensional and three-dimensional cross-linked structure units, resulting in a synergistic effect. The Zn2+/Fe3+(1:1)-SA-PAm/PNIPAm-HACC bilayer-actuated hydrogels have excellent antibacterial properties, shape fixation (85.4 %), fatigue resistance, and reversibility, and showed rapid, reversible, and reproducible thermoresponsive bending/unbending properties, which can be prepared as an actuator, such as a gripper to capture, transport, and release an object, or a temperature-controlled device to turn on and off indicator lights. Overall, this hybrid ion-crosslinked bilayer hydrogel can provide new insights into the design and fabrication of smart actuators.

Design and performance analysis of a novel class of SMA-driven rotational mechanisms/joints

AbstractThe rotational joint plays a vital role in the industrial and civil areas, which is typically utilized to achieve the relative rotation between the adjacent parts. Generally, structuring a conventional rotational joint involves the bulk actuators (e.g., motor and hydraulic cylinders) and complex structures, bringing difficulty for miniaturing the dimension. In this paper, a class of novel rotational mechanisms, which were constructed by the combination of compliant mechanisms (e.g., cartwheel pivot and multileaf pivot) and intelligent actuator (e.g., shape memory alloy (SMA) wire and spring), was proposed to reduce the complexity of the conventional rotational joints. As the case study, a novel SMA wire-driven flexural rotational mechanism (SDFRM), which is constructed by the cartwheel pivot and SMA wire, was developed to demonstrate the feasibility of combining the compliant mechanism and smart actuator. After establishing the static model of the cartwheel pivot and the thermal effect model of the SMA wire, the overall model of SDFRM was developed for the comprehensive performance analysis and the control system design. After that, the model validation and experiments were performed with the proposed prototype and control system. It can be seen from the experimental results that the proposed model can be validated within the error of 3.8%. In addition, the performance study on SDFRM indicates that the prototyped SDFRM system can track the given trajectories within the error of 0.2 mm in the workspace. As a result, the proposed concept was demonstrated as an effective way to reduce the dimension and weight of the conventional rotational joint.

Octopus Inspired Hydrogel Actuator with Synergistic Structural Color and Shape Change

AbstractLiving organisms in nature, such as chameleon and octopus, have amazing performances by changing their color and shape simultaneously for camouflage. Inspired by the camouflage behaviors of octopus, an intelligent hydrogel actuator with tunable structural color is presented in this work. The actuator is fabricated by a typical bilayer of active poly(N‐isopropylacrylamide) (PNIPAM) hydrogel layer and inert poly(acrylamide‐acrylic acid) hydrogel layer, which endows the actuator shape‐changing by temperature stimulus. The only difference about this actuator is a thin layer of thermoresponsive microgels film embedded into the PNIPAM hydrogel layer, and thus tunable structural color can be displayed with the shape‐changing of the actuator. This makes the preparation procedure straightforward and environment‐friendly. Moreover, when multi‐wall carbon nanotubes are incorporated into the hydrogel, the color and shape of the hydrogel can be controlled via remote near‐infrared irradiation. This smart hydrogel actuator would be of benefit in various fields such as grippers, and soft robots with dynamic camouflage.

Intelligent controller for robust orientation control of smart actuator based parallel manipulator

Flexible parallel manipulators can be used as an orienting device due to its precise positioning ability. The flexibility demands the use of non-conventional actuators and noncontact type/flexible sensors for feedback measurement. This study proposes a novel 2 Degree of Freedom (DoF) parallel manipulator actuated by shape memory alloy springs (SMA) which could be used as an orienting device for a table top Cartesian robot. To mitigate the use of contact type sensor, model based feedback is proposed to obtain SMA length for the feedback control. The inclusion of SMA actuators to parallel mechanism imposes control challenges due to nonlinearities, coupling effects, and disturbances. This work also proposes a novel control scheme based on concept of partition control law to control the SMA spring position without the use of any complex mathematical model. The proposed controller is a combination of two parts Fuzzy PID servo control and the time delay estimation (TDE) based auxiliary control. The fuzzy PID control handles the error tracking and the auxiliary control tries to cancel the nonlinearities and disturbances, thus enhancing the robustness. The performance of the proposed controller is tested for a complex trajectory under disturbances and the results are compared with existing nonlinear controllers which proves superior nature of the proposed controller.

Hierarchically Structured Hydrogel Actuator for Microplastic Pollutant Detection and Removal

The aquatic microplastic pollution has aroused worldwide concerns due to its potential risk to biological and ecological health, especially the microplastic compound pollutants (MCPs) with amplified biotoxicity. Self-powered soft robots integrating with simultaneous MCP detection and removal capacities represent an intelligent way to clear the contaminants from water, but it is still challenging to implement these properties in one single actuating material. Here, we propose a smart light-driven hydrogel actuator with hierarchical interpenetrating networks consisting of covalently bonded polyethyleneimine and polydopamine copolymers, graphene oxide nanosheets, and poly(N-isopropylacrylamide) hydrogels, which function as adsorbents for MCPs, photothermal converters, and actuating matrix, respectively. Thanks to the integrative hierarchical structure design, the resulted actuator can behave like a soft swimming robot to simultaneously identify and adsorb MCPs, which successfully incorporates multiple functionalities without compromising the responsiveness. The hydrogel actuator features an ultralow detection limit (0.98 μM for the ferric ion), excellent adsorbing selectivity (97.09% for ferric ion-adsorbed MCPs), high adsorption (94.63%) and desorption efficiency (99.12%), and multiple and untethered photothermal actuation performances. We believe this work will shed light on a promising construction strategy of intelligent soft robots for environmental remediation applications.

Experimental analysis of fiber-reinforced laminated composite plates with embedded SMA wire actuators

Shape memory alloy (SMA) wires are effective smart actuators since they provide relatively large actuation force and strain in a very limited space. Embedding SMA wires in flexible laminated composite plates or shells allows for creating active structures for morphing applications. However, the design of such structures is challenging due to the nonlinear thermomechanical coupling of SMA materials, the adhesion of the SMA actuators to the resin, the effect of temperature on the adhesion strength, the heat transfer between the SMA wires and the surrounding laminate, and the convection boundary conditions. This paper presents an experimental analysis of smart fiber-reinforced composite laminated plates with embedded SMA wires, focusing on the relationship between the applied electric current, measured temperature of the SMA wires, and the resulting tip deflection. A temperature-based control method was developed to achieve the required wire temperature and tip deflection as quickly as possible. Results showed that the fiber-orientation angle of the composite plies and the convection boundary conditions have significant effects on the structure’s actuation. With cyclic actuation, damage starts around the heated SMA wires and can grow to cause delamination at areas between neighboring SMA wires and yielding of the matrix material, resulting in permanent deformation.

New Challenges towards Smart Systems’ Efficiency by Digital Twin in Water Distribution Networks

Nowadays, in the management of water distribution networks (WDNs), particular attention is paid to digital transition and the improvement of the energy efficiency of these systems. New technologies have been developed in the recent years and their implementation can be crucial to achieve a sustainable level of water networks, namely, in water and energy losses. In particular, Digital Twins (DT) represents a very innovative technology, which relies on the integration of virtual network models, optimization algorithms, real time data collection, and smart actuators information with Geographic Information System (GIS) data. This research defines a new methodology for an efficient application of DT expertise within water distribution networks. Assuming a DMA of a real water distribution network as a case study, it was demonstrated that a fast detection of leakage along with an optimal setting of pressure control valves by means of DT together with an optimization procedure can ensure up to 28% of water savings, contributing to significantly increase the efficiency of the whole system.

Dual‐responsive smart actuator based on Ti3C2Tx/polymer bilayer structure for bionic applications

Intelligent actuators are emerging smart electronic devices, that sense external stimuli (such as light, heat, electricity, et al.) and convert them into mechanical energy. They have been widely used in biomedicine, micro or biomimetic robots, artificial muscles, switches, and microsensors. MXenes are a series of new two-dimensional materials. Among them, a representative MXene is Ti3C2Tx. Compared with other MXenes, Ti3C2Tx has the advantages of high thermal conductivity, adjustable structure, chemical stability, surface hydrophilicity, and et al. To date, Ti3C2Tx has been extensively researched. Many kinds of research have been achieved in the fields of sewage treatment, flexible sensors, electromagnetic interference shielding, energy storage/conversion, etc. However, the application of Ti3C2Tx in multi-responsive actuators is rarely mentioned. Here, we propose a bilayer actuator fabricated by a simple hot pressing method that can respond to the stimuli of electricity and light. Thanks to the high electrical conductivity, strong light absorption ability, and low thermal expansion coefficient of Ti3C2Tx, the Ti3C2Tx/polymer actuator driven by the dual stimuli of electricity and light can be obtained when combined with polymer film with a large thermal expansion coefficient. When a driven voltage of 6 V is applied to the Ti3C2Tx/polymer actuator, it will bend toward the direction of the Ti3C2Tx layer, with a bending curvature of 0.5 cm-1. The Ti3C2Tx/polymer actuator can also exhibit a large (0.51 cm-2) and reversible bending deformation under near-infrared light (500 mW cm-2) irradiation. In addition, an electric-driven smart gripper and a light-driven bionic worm were designed to demonstrate the actions of moving objects and crawling. These results not only provide new inspiration for using Ti3C2Tx to design high-performance soft actuators but also reveal the potential of Ti3C2Tx -based actuators in smart devices.

Finite-time active fault-tolerant attitude control for flexible spacecraft with vibration suppression and anti-unwinding

In this paper, a finite-time active fault-tolerant control scheme is designed for a flexible spacecraft’s attitude control experiencing inertial parametric variations, external disturbances, multiple actuator faults, and estimation errors while suppressing the flexible appendages’ vibrations without using smart vibration suppression actuators. First, relative attitude dynamics of a flexible spacecraft with multiple actuator faults are outlined, and a sliding mode observer is designed to estimate flexible appendages-related vibrations. The proposed fault detection and identification (FDI) strategy can efficiently detect actuator faults, avoiding the false alarms caused by uncertainties and disturbances, and accurately estimate the cumulative fault effects on the spacecraft via Chebyshev neural network (CNN) based estimator. Based on a novel fast nonsingular terminal sliding mode surface, a finite-time, unwinding-free, and adaptive fault-tolerant attitude controller is designed to acclimatize the detected faults and uncertainties effectively, also heeding the errors in the estimation of flexible modes and faults. The spacecraft can carry out the coveted control objective in a definable time, and the stability of the proposed controller is corroborated via Lyapunov techniques. Finally, a comparative simulation analysis with the existing results elucidated the proposed scheme’s efficacy.

Efficient voltage actuators based on rapid heat and electric dual-response poly(aryl ether ketone) shape memory composites reinforced with radially aligned CNTs

In this paper, we synthesized the shape memory poly(aryl ether ketone) (PAEK) and fabricated the radially oriented CNTs enhanced PAEK composite actuators. The introduction of highly aligned CNTs endowed PAEK matrix great thermal stability, good mechanical properties, and excellent shape memory effect. The formation of CNTs conductive path in PAEK matrix was instrumental in improving thermal and electrical conductivity, promoting efficient heat/electric dual triggered shape memory effect with high recovery ratio, rapid shape recovery and low triggering voltage. In addition, we used aligned CNTs/PAEK composites with 15 wt% CNTs as voltage actuators, and designed the two kinds of voltage actuators (angle-mode and time-mode) to achieve the different actuating actions via the applied voltage (range from 8 V to 50 V). These efficient composite voltage actuators exhibited the excellent stability and durability in continuous voltage actuating, which were expected to open door for smart actuators and electronic devices.

Reprogrammable, light-driven and sensing actuators based on Chinese ink composite: A synergetic use of shape-memory and self-healing strategies

Smart actuators have great prospects in soft robotics. Reprogrammable function is essential for shape-reprogramming of actuators to achieve arbitrary shapes and diverse deformations, which is a key feature for next-generation actuators. However, it remains a huge challenge to develop a facile strategy to prepare reprogramming and multi-functional actuators. Herein, we report a synergetic strategy to fabricate reprogrammable, light-driven and sensing actuators based on Chinese ink and waterborne polyurethane (PU) composite. The entire ink/PU actuator is self-healing, as both the ink and PU films can be self-healed with the aid of water. Through synergistically using the shape-memory of PU and self-healing property of ink/PU composite, the initial configurations of ink/PU actuators can be fixed and assembled into arbitrary shapes, including tendril-shape, heart-shape, accordion-shape, letter-shapes and so on. These programmed actuators demonstrate complex deformations reversibly under near-infrared light irradiation. Importantly, the same actuator can be reprogrammed and light-actuated again. Moreover, introducing conductive ink layer integrates temperature sensing function into the actuator. Finally, a bionic butterfly robot is constructed, which can not only flap wings under light irradiation, but also sense human touching. This study will open a new path to reprogrammable, self-healing, and light-driven soft robots with multi-functions and complex deformations.

Packaging 4.0: The threshold of an intelligent approach.

The fourth industrial revolution (I4.0) intends to digitalize the product life cycle using smart technologies interconnected with web-based platforms. I4.0 elements can be employed to enable packaging 4.0 with improved productivity and efficiency. However, the applicability of I4.0 in packaging science has not been fully investigated due to the understanding gap regarding the I4.0 elements in packaging science. In addition, the evolution of market and customers' demands results in complexity, which requires a business model with a high level of precision. As packaging stays with goods from manufacturing to the consumer stage, the digitalization of the product life cycle using packaging can be realized. Herein, the implications of I4.0 on packaging science are discussed to identify the potential benefits of packaging 4.0 in various sectors, for example, manufacturing, materials, supply chain, retail, and postconsumer. In this study, packaging 4.0 is defined based on a framework comprised of packaging manufacturing, packaging and products, packaging and consumer, and packaging and sustainability (ecologically, economically, and socially). In addition, a decentralized model is introduced to realize a self-controlling concept using decentralized decision-making centers. In this context, packaging 4.0 can be enabled using the combination of horizontal integration of enterprises, vertical integration of enterprises, and end-to-end engineering. Smart devices, for example, sensors, indicators, actuators, and wearable smart devices, interconnected to the internet of things and the cloud is an efficient way to realize a decentralized paradigm. The implementation of an intelligent platform in the packaging 4.0 context enables decentralized data collection in the supply chain, in-store, and postpurchasing stages, which in turn realizes consistent life-cycle monitoring.

Bioinspired bilayer hydrogel-based actuator with rapidly bidirectional actuation, programmable deformation and devisable functionality

Smart hydrogel actuators which respond to external stimuli have attracted great attention and shown good application prospects in many fields as their simplicity and reliability, while the challenges remain in terms of the relatively low driving force, responsive velocity and deformation amplitude considering the structure-dependent actuation behavior. Here, we propose a thermosensitive hydrogel-based actuator with bioinspired bilayer structure by applying a textured airlaid paper to induce the formation of heterogeneous construction. This nature-inspired design benefits the hydrogel-based actuator rapidly bidirectional actuation, realizing excellent bending velocity (140.6° s−1 within first 5 s) and bending amplitude (850.0° within 30 s) in hot water, powerful recovery in cool water and remarkable reproducibility upon external environmental stimulus by optimizing the texture orientation and mechanical property of airlaid paper. The excellent bonding between airlaid paper and hydrogel also endows the actuator satisfactory stability for circularly operation under water environment for weeks. The programmable deformation and devisable functionality are further realized by propagable and elaborate design for architecture and component of responsive hydrogel, favoring the hydrogel-based actuator alterable ethanol-sensitive ability, photothermal drivability and regenerability. This bilayer hydrogel-based actuator provides promising potentials for the applications in soft robots, smart actuators, artificial muscles, and intelligent human-machine technologies.