Reliability Of Actuators Research Articles

Moisture-triggered hybrid soft actuator and electric generator for self-sensing wearables and adaptive human-environment interaction

As ubiquitous energy available from the human body and surrounding environment, moisture converted into both mechanical and electrical energy simultaneously offers appealing strategies for adaptive self-sensing wearables. However, most energy conversion devices typically achieve only single-form energy conversion. Here, we report an integrated device concept that breaks this limit—a moisture-triggered hybrid soft actuator and electric generator (MTAEG) capable of generating reliable actuation and superior electrical output concurrently. By utilizing printable asymmetric electrodes and hygroscopic polyelectrolyte composite film, we achieve the all-in-one device with hybrid functionalities for effective moisture-energy conversion. The MTAEG demonstrates reversible stable actuation (125° bending angle at 80 % RH) and offers a current density of up to 76.41 μA cm−2, accompanied by a power density of 11.24 μW cm−2. This outstanding electrical performance exceeds that of most reported conventional moist-electric generators, thanks to the optimization of asymmetric electroactive electrodes and the excellent ion-transport ability of the polyelectrolyte composites. Moreover, MTAEGs can be compatibly integrated into arrays for various applications, including bioenergy modules, self-powered tracking/sensing, adaptive personal comfort management, and physical activity monitoring. Such printable MTAEGs with ingenious materials combinations, high-throughput fabrication, and attractive performance offer a promising hybrid platform for self-sensing wearables and adaptive human-environment interaction.

Multiphysics modeling and optimization of an innovative shape memory alloy-polymer active composite

Shape memory alloys (SMAs) are a unique class of smart materials capable of recovering significant deformations through temperature variations, making them attractive for adaptive structures and morphing applications. However, integrating SMAs into polymer composites poses significant challenges, such as interfacial delamination and matrix overheating during thermal activation, in addition predicting the stress acting on the SMA during the actuation is pivotal. Addressing these issues is crucial for realizing the full potential of SMA-based active composites in aerospace, automotive, and renewable energy sectors. This study presents a novel multi-material design strategy for SMA-polymer active composites, featuring a rigid PC/ABS layer for mechanical integrity, a soft high-temperature silicone coating for encapsulating SMA wires, and aluminum terminals for wire crimping. A comprehensive multiphysics FEM model was developed to accurately capture the coupled thermo-mechanical response. Extensive experimental characterization and validation were conducted, followed by systematic parametric studies to investigate the effects of critical design parameters on key performance metrics. The developed prototype exhibited remarkable shape morphing capabilities, with a maximum tip deflection of 68 mm (deflection-to-length ratio of 0.4). Excellent agreement between experiments and simulations was achieved, with a maximum error of 1.7 % in tip deflection, validating the accuracy of the multiphysics model. Parametric analyses quantified the trade-offs between geometric parameters, revealing their influence on activation temperature, deflection, SMA wire stress, and fatigue life. Optimal configurations enabling low activation temperatures (<150 °C), low stress levels (<400 MPa), and high predicted fatigue life (>50,000 cycles) were identified. The multi-material design approach effectively addressed common issues in SMA-polymer composites, enabling reliable actuation cycles without damage accumulation. The validated multiphysics model and parametric insights provide a comprehensive framework for optimizing the design and performance of SMA-polymer active composites, paving the way for their widespread adoption in shape morphing applications. Potential implications include the development of adaptive aerodynamic surfaces, deployable structures, and energy-efficient systems across various industries.

Ultrarobust Actuator Comprising High-Strength Carbon Fibers and Commercially Available Polycarbonate with Multi-Stimulus Responses and Programmable Deformation.

Polymer-based actuators have gained extensive attention owing to their potential applications in aerospace, soft robotics, etc. However, poor mechanical properties, the inability of multi-stimuli response and programmable deformation, and the costly fabrication procedure have significantly hindered their practical application. Herein, these issues are overcome via a simple and scalable one-step molding method. The actuator is fabricated by hot-pressing commercial unidirectional carbon fiber/epoxy prepregs with a commodity PC membrane. Notable CTE differences between the CF and PC layers endow the bilayer actuator with fast and reliable actuation deformation. Benefiting from the high strength of CF, the actuator exhibits excellent mechanical performance. Moreover, the anisotropy of CF endows the actuator with design flexibility. Furthermore, the multifunction of CF makes the actuator capable of responding to thermal, optical, and electrical stimulation simultaneously. Based on the bilayer actuator, we successfully fabricated intelligent devices such as light-driven biomimetic flowers, intelligent grippers, and gesture-simulating apparatuses, which further validate the programmability and multi-stimuli response characteristics of this actuator. Strikingly, the prepared gripper possesses a grasping capacity approximately 31.2 times its own weight. It is thus believed that the concept presented paves the way for building next-generation robust robotics.

An analysis of biomechanical requirements and actuating technologies of biomimetic hand exoskeletons regarding to driving force and stroke

Exoskeletons have gained importance recently. In the case of musculoskeletal diseases, they can restore or support the mobility of injured body parts; in everyday life, they can relieve the musculoskeletal system and thus contributes to the preservation of health into old age. However, active systems face challenges due to the efficient and reliable actuators. In the following, the example of the hand will be used to investigate what influence the individuality of the hand under consideration has on the selection of a suitable actuator about force and stroke.The literature outlines that tendon-driven mechanism with a biomimetic design are a promising approach for hand exoskeletons: The finger is actively moved by an actuator using artificial tendons positioned along the finger to match anatomical structures. For this purpose, actuators based on electromagnetic or pneumatic principles, and smart materials are described. The requirements for force and stroke of the drive can be derived from the analysis of finger kinematics. In this study the finger kinematics of 13 subjects were analyzed. The results show a scatter in stroke and force depending on the finger considered. To select a suitable actuator for the biomimetic hand exoskeleton, these results are compared with the force and stroke characteristics of various actuating principles. The comparison reveals that the choice of the actuator depends on the intended primary support for the hand (movement, endurance, grip strength). Hence, it can be deduced that step drivers meet the force and stroke requirements and may be a suitable alternative.

Optimal Design of Motor–Pump Parameters for Direct Load-Sensitive EHA Based on Multi-Objective Optimization Algorithm

The electro-hydrostatic actuator (EHA) is a highly integrated and reliable actuation system which has been widely used in aerospace and construction machinery. In addition, the direct load sensitive EHA (DLS–EHA) has been investigated by introducing load-sensitive techniques which can well match the system output and external loads. More importantly, the matching design of motor–pump parameters is an important stage in the pre-design phase of DLS–EHA. For this reason, a multi-objective optimization design method for DLS–EHA motor–pump parameters is proposed in this paper. Firstly, the motor–pump mass and energy loss models are constructed based on similarity criteria. Secondly, the multi-objective particle swarm optimization algorithm (MOPSO) is used to optimize the design of the motor-pump parameters, and the Pareto frontier solutions of the optimized parameters are obtained. Further, the optimal design parameters are selected on the basis of meeting the actual requirements. Finally, the DLS–EHA prototype is designed based on the optimized design parameters and experimental verification is completed. The results of the study show that the optimized design parameters can meet the design requirements. The design method proposed in this paper provides an important theoretical basis for the optimized design of DLS–EHA.

Interface dewetting as a source of void formation and aggregation in phase change nanoscale actuators

This paper reports a phenomenon occurring between phase change material (PCM) germanium telluride (GeTe) and a thin encapsulation layer of alumina when the PCM undergoes the phase transformation, consistent with dewetting of the PCM from the surrounding alumina. Massive structural change, including formation of large voids, which take up to 21.9% of the initial GeTe volume after 10 000 phase change cycles is observed. Electrical and mechanical characterization of the structure confirms this interpretation. A rapid thermal annealing test of blanket films on alumina that demonstrates dewetting further validates this conjecture. The dewetting and associated gross material displacement can lead to an extraordinary actuation corresponding to a one-time 44 nm height change for a 178 nm GeTe thick layer. However, control of this phenomenon is required to build reliable actuators that do not suffer from rupture of the encapsulation layer.

Characteristics of a Fluidic Oscillator with Low Frequency and Low Speed and Its Application to Stall Margin Improvement

Active flow control methods are commonly used in expanding the operating range of compressors. Indeed, unsteady active control methods are the main focus of researchers due to their effectiveness. For constructing an unsteady active control system, reliable actuators are significant. To compare with conventional actuators such as synthetic jet actuators and rotating valves, fluidic oscillators have structurally robust characteristics and can generate self-excited and self-sustained oscillating jets, which leads to its higher applicability in compressors under severe working conditions. Thus, to explore the feasibility of unsteady active control systems by the usage of fluidic oscillators, a low-frequency and low-speed oscillator is first designed and experimentally studied for improving the stability of a low-speed axial flow compressor. During the experiments, a special casing is designed to install 15 uniformly distributed oscillators in the tip region of compressor. Based on the unsteady micro injections of the rotor tip with rotor rotation frequency, the results indicate that the frequency/period of oscillators are flexible, in which the values are decoupled with the variation of inlet pressure. When the inlet-to-outlet pressure ratio of the oscillator is in the range of 1.1~2.0, the maximum velocity ranges from 30 m/s to 80 m/s. Moreover, the mass flow rate of the single oscillator only varies from 0.017‰ to 0.059‰ from the designed compressor mass flow rate. For the improvement of the compressor stall margin, the value is 3.45% when the total mass flow of oscillators is 0.08% of the designed compressor mass flow.

Knot‐Architectured Fabric Actuators Based on Shape Memory Fibers

AbstractDue to recent progress on wearable robotics, developing high‐performance fabric and textile actuators to be integrated with various soft electronic devices is urgently needed and remains a challenging issue. Here, a novel knot‐architectured fabric actuator (KAFA), showing superior features such as self‐locking crossing, mechanical robustness, facile fabrication at very low cost, high force generation, and large actuation strain, is reported. The actuation principle of KAFA is based on the shape recovery of constituent nitinol fibers that can restore the memorized curvature in the knotted architectures. Further, the KAFA can be conveniently operated by Joule heating, resulting in reliable actuation due to its seamlessly conductive circuit network. In addition, the KAFA shows exceptionally high force, up to 1373 times its own weight and around 30% actuation strain. The newly developed fabric actuators are applied to a wearable actuation device to lift weighty luggage and an adaptive controllable surface to grip spiky, irregular, fragile, and slippery objects. These applications demonstrate the wide potential of KAFAs for future wearable robotic products such as rehabilitative devices and powered exoskeletons.

Multilayer Graphene/PDMS Composite Gradient Materials for High‐Efficiency Photoresponse Actuators

AbstractSmart actuating materials have a wide range of applications in artificial muscles, soft robots, and flexible electronics. The preparation of highly sensitive and reliable actuators is a top priority in this regard. In this work, a multilayer graphene/polydimethylsiloxane (PDMS) composite gradient material is designed and prepared by a simple in situ stacking and curing method for high‐efficiency photoresponse actuator. The typical gradient structured material consists of a pure PDMS film and multiple graphene/PDMS composite films with monotonically varying graphene concentration. Attributed to gradient structure design and high photothermal conversion efficiency of graphene, the actuator shows the enhanced photoresponse properties. Through theoretical modeling, finite element analysis and experiments, it is confirmed that with increasing the stacked layer number at the same total thickness, the gradient structured actuator can present a better actuation performance. In addition, the film thickness and the concentration of graphene are also found to have an obvious effect on the actuating behavior, enabling the deflection over 90°. The applications of the actuator as a cantilever beam, a soft crawling robot and a smart gripper are also demonstrated. This provides a new design idea for further improving the actuation performance of the soft actuator.

Comparison of Under-Actuated and Fully Actuated Serial Robotic Arms: A Case Study

Abstract Under-actuated robots are very interesting in terms of cost and weight since they can result in a state-controllable system with a number of actuators lower than the number of joints. In this paper, a comparison between an under-actuated planar three-degrees-of-freedom (DOF) robot and a comparable fully actuated two-degrees-of-freedom robot is presented, mainly focusing on the performances in terms of trajectories, actuator torques, and vibrations. The under-actuated system is composed of two active rotational joints followed by a passive rotational joint equipped with a torsional spring. The fully actuated robot is inertial equivalent to the under-actuated manipulator: the last link is equal to the sum of the last two links of the under-actuated system. Due to the conditions on the inertia distribution and spring placement, in a simple point-to-point movement the last passive joint starts and ends in a zero-value configuration, so the three DOF robot is equivalent, in terms of initial and final configuration, to the two DOF fully actuated robot, thus they can be compared. Results show how while the fully actuated robot is better in terms of reliable trajectory and actuator torques, the under-actuated robot wins in flexibility and in vibrations at a given configuration.

Enabling Optimal Energy Management with Minimal IoT Requirements: A Legacy A/C Case Study

The existing literature on energy saving focuses on large-scale buildings, wherein the energy-saving potential is substantially larger than smaller-scale buildings. However, the research intensity is significantly less for small-scale deployments and their capacities to regulate energy use individually, directly and without depreciating users’ comfort and needs. The current research effort focused on energy saving and user satisfaction, concerning a low-cost—yet technically sophisticated—methodology for controlling conventional residential HVAC units through cheap yet reliable actuation and sensing and auxiliary IoT equipment. The basic ingredients of the proposed experimental methodology involve a conventional A/C unit, an Arduino microcontroller, typical wireless IoT sensors and actuators, a configured graphical environment and a sophisticated, model-free, optimization-and-control algorithm (PCAO) that portrays the ground basis for achieving improved performance results in comparison with conventional methods. The main goal of this study was to produce a system that would adequately and expeditiously achieve energy savings by utilizing minimal hardware/equipment (affordability). The system was designed to be easily expandable in terms of new units or thermal equipment (expandability) and also to be autonomous, requiring zero user interventions at the experimental site (automation). The real-life measurements were collected over two different seasonal periods of the year (winter, summer) and concerned a conventional apartment in the city of Xanthi, Northern Greece, where summers and winters exhibit quite diverse climate characteristics. The final results revealed the increased efficiency of PCAO’s optimization in comparison with a conventional rule-based control strategy (RBC), as concerns energy savings and user satisfaction.

Experimental Investigation of Performance, Reliability, and Cycle Endurance of Nonvolatile DC–67 GHz Phase-Change RF Switches

This article reports high-performance and reliable phase change material (PCM) germanium telluride (GeTe)-based nonvolatile radio frequency (RF) switches. The highly miniaturized ultrawideband dc to 67 GHz millimeter-wave (mmWave) switches is developed in-house using a custom eight-layer microfabrication process. The switches are fully passivated and do not require any special packaging for integrating heterogeneously with other technologies. They are also amenable to monolithic integration with a wide range of RF devices on a single chip, such as phase shifters, impedance tuners, and attenuators, to name a few. The PCM GeTe-based RF switches are experimentally tested for their RF performance variation across the wafer, performance change at high temperature, high-power handling capability, third-order intercept (TOI) through the two-tone testing setup, and switching speed. The nonvolatile resistance state reliability of the PCM switches is experimentally investigated. The presented RF switches are cycled more than one million times, demonstrating reliable actuation operation with a figure of merit exceeding 14.5 THz. A detailed description of the experimental setup for measuring the switching speed, power handling capability, linearity, reliability, and cycle endurance assessment of the PCM switches is presented. The PCM switches developed are compared with the current state-of-the-art demonstrating a clear improvement in various aspects of the switch’s performance.

A survey on electro hydrostatic actuator: Architecture and way ahead

The nascent development in the field of the hydraulic actuator is the integration of various cutting edge technology like mechanical, hydraulic, control and electrical the result is the multidisciplinary final product which is high-performance Electro Hydrostatic Actuator (EHA). This is an independent direct actuation method which is also known as “power-by-wire” (PBW) technology. This technology is design to replace the cumbersome leak-prone centralized hydraulic system with a compact and reliable actuation system. This technology originally developed for flight control application but due to enhance reliability and increasing popularity currently, it is being used in many industrial applications for different purposes. This paper attempt to bring out the component level comprehensive insight of EHA and consolidate all available literature of this field in the form of literature survey. These papers also talk about the pros and cons of the system and various control methods to curb noted disadvantages. Most of the existing research literature considers the EHA with an asymmetrical cylinder which is widely used in aircraft. However, in industrial application, the asymmetrical cylinder is most suited and predominately used. The control of asymmetrical cylinder poses a greater challenge vis-a-vis symmetrical cylinder due to differences in the area of two-chamber. This paper also tries to throw some light on the methods of controlling the cylinders. Finally, this paper concludes by finding research gaps and further scope of improvements and application of EHA in armoured recovery vehicles.

Kinematic analysis of a rolling tensegrity structure with spatially curved members

In this work, a tensegrity structure with spatially curved members is applied as rolling locomotion system. The actuation of the structure allows a variation of the originally cylindrical shape to a conical shape. Moreover, the structure is equipped with internal movable masses to control the position of the center of mass of the structure. To control the locomotion system a reliable actuation strategy is required. Therefore, the kinematics of the system considering the nonholonomic constraints are derived in this paper. Based on the resulting insight in the locomotion behavior a feasible actuation strategy is designed to control the trajectory of the system. To verify this approach kinematic analyses are evaluated numerically. The simulation data confirm the path following due to an appropriate shape change of the tensegrity structure. Thus, this system enables a two-dimensional rolling locomotion.

Magnetic Actuation Systems for Miniature Robots: A Review

A magnetic field, which is transparent and relatively safe to biological tissue, is a powerful tool for remote actuation and wireless control of magnetic devices. Furthermore, miniature robots can access complex and narrow regions of the human body as well as manipulate down to subcellular entities; however, integrating onboard components is difficult due to their limited size. Combining these two technologies, magnetic miniature robots have undergone rapid development during the past two decades, mainly because of their high potential in medical and bioengineering applications. To improve the scientific and clinical outcomes of these tiny agents, developing suitable and reliable actuation systems is essential. As a newly emerging field that has progressed in recent years, magnetic actuation systems offer a harmless and effective approach for the remote control of miniature robots via a dynamic magnetic field. Herein, a review on the state‐of‐the‐art magnetic actuation systems for miniature robots is presented with the goal of providing readers with a better understanding of magnetic actuation and guidance for future system design.

Reliable actuator fault control of positive switched systems with double switchings

AbstractThis paper proposes a novel double switchings reliable control for positive switched systems. Double switchings refer to the switchings of subsystems and faults. Considering the actuator faults during the system operation, a class of periodic switched actuator faults is first considered. A reliable controller is designed using linear copositive Lyapunov functions and an average dwell time switching rule is presented for the systems. Then, two average dwell time switching rules are given for the subsystems and the faults, respectively. A corresponding reliable controller is proposed in terms of linear programming. Compared with existing results, the novel approach contains three advantages: (i) the actuator faults of subsystems are allowed to be varying, (ii) two classes of detailed double switchings rules are designed, and (iii) the presented reliable control framework provides a new methodology to deal with the reliable control problem of general switched systems with faults. Finally, two examples are given to illustrate the validity of the presented results.

Stimuli-responsive superhydrophobic films driven by solvent vapor for electric switch and liquid manipulation

Fabrication of functional superhydrophobic materials with stimuli-responsive driving ability for the growing fields such as electric switch and liquid manipulation still remains mysterious and challenging. In this work, a stimuli-responsive superhydrophobic film (SSF) is fabricated by integrating a bottom porous poly(vinylidene fluoride) (PVDF) layer, a sandwiched cross-linkable poly(vinyl alcohol) (cPVA) layer, and a top carbon nanotubes@polydimethylsiloxane (CNTs@PDMS) layer. Induced by the asymmetric swelling of cPVA/PVDF bilayer upon exposure to acetone vapor, the SSFs directionally roll towards the superhydrophobic CNTs@PDMS surface with a large curvature of 0.65 mm−1, a fast response within 10 s, and an excellent fatigue resistance of more than 1000 actuation cycles. Furthermore, the special superhydrophobicity highly ensures the reliable actuation behavior of the SSFs under wet environments. Taking advantage of the conductivity of the CNTs@PDMS layer, the SSF-based electric switches are fabricated and conveniently actuated to control the electric circuit states of turning on/off. Additionally, thanks to the combination of water repellency and acetone vapor-responsive actuation, the SSFs are designed as smart channels for a water control system to successfully achieve the manipulation of liquid flow direction. The findings conceivably stand out as a new methodology to fabricate functional superhydrophobic materials with stimuli-responsiveness for various potential applications.

Electrostatic field induced coupling actuation mechanism for dielectric elastomer actuators

Dielectric elastomer actuators (DEAs) exhibit many fascinating advantages, including high compliance, large actuation strain, fast response, high energy density and efficiency. These muscle-like properties make them suitable for robotic and mechatronic applications especially the actuation of soft robots. However, such actuators have experienced high rates of failure when operating at high voltage, which impedes their practical application to some extent. Here, we report an enhanced and reliable actuation mechanism which couples the electrostatic induction actuation and the electrostatic attraction or zipping mechanisms for DEAs. A circular DEA (E-DEA), a zipping DEA (EZ-DEA) and a bending DEA (E-DEMES) are redesigned and fabricated using this mechanism, which both survive the pull-in electromechanical instability and demonstrate higher operational voltages, larger attainable deformations, and longer actuation lifetime. The E-DEA achieves a large area strain up to 174% and can sustain 20-kV or even higher voltage, its equivalent dielectric strength is larger than 877 MV/m. The EZ-DEA achieves a larger out-of-plane deformation up to 8 mm compared to the traditional zipping DEAs. The E-DEMES is promoted 5 times in response speed and maximally about 87% in the transient blocking force. The improved E-DEMES also exhibits a great potential in faster actuation, larger actuation stroke and force for soft robots.

Designing Mechatronic Musical Instruments: The Guitar

Since the earliest times, humans have sought the ability to produce rhythms and tones using devices external to the human body. As technology developed, so too did the desire for this sound production to become automated. Initially peaking around the Industrial Revolution, traditional automated musical production devices went into a steep decline with the arrival of the phonograph. However, factors such as the ubiquitous acceptance of the microcontroller led to a resurgent interest in this field. This paper investigates the design considerations and development of the stringed chordophone and specifically the guitar. The challenge is to produce a mechatronic device capable of speedy and reliable note selection, string actuation, string damping and expressiveness. In the same manner that there is not one best way to play a guitar and no best guitar design, so too is there no “best” chordophone design. Rather, the competing factors of speed, precision, reliability, portability, expressiveness and timbral variation can be given different weightings and result in different designs. Therefore, rather than presenting a single chordophone development, this paper provides a multitude of design options providing an interested reader with the background and suggestions to create their own bespoke design. This paper concludes with the presentation of the authors’ final design as an integration of the presented ideas and design techniques. We demonstrate that this chordophone introduces expressivity at a level not achieved before, is modular yet portable, is mechanically quiet and can play at a speed beyond that of even the best human player.

Compatibilization of porphyrins for use as high permittivity fillers in low voltage actuating silicone dielectric elastomers.

Polysiloxanes represent, because of their unusual properties, a material with great potential for use in dielectric elastomers (DEs), a promising class of electroactive polymers. Currently, their application as actuators is limited by the need for high driving voltages, as a result of the low relative permittivity possessed by polysiloxanes (∼2–3). Reducing these voltages can be achieved to some degree by using high permittivity additives to improve the permittivity of the polysiloxane. However, modifying such additives so that they are compatible with, and can be dispersed within, polysiloxane elastomers remains challenging. For reliable actuation, full miscibility is key. In this work the porphyrin 5,10,15,20-(tetra-3-methoxyphenyl)porphyrin (TPMP) was investigated as a high permittivity additive. Its behaviour was compared to the analogue that was derivatized with bis(trimethylsiloxy)methylsilane groups using the Piers–Rubinsztajn reaction to improve compatability with silicone formulations. The derivatized porphyrin was dispersed in elastomers and their dielectric and mechanical properties were evaluated. It was discovered that only low levels of incorporation (1–10%) of the siliconized TPMP – much lower than the parent TPMP – were needed to elicit improvements in the permittivity and electromechanical actuation of the elastomers; actuation strains of up to 43% could be achieved using this method.