High Actuation Research Articles

Silicon-based dielectric elastomer with amino-complexed hybrids towards high actuation performance

For improving the actuation performance at low electric fields of dielectric elastomers, achieving high dielectric constant (ɛr) and low modulus (Y) simultaneously has been targeted in the past decades, but there are few ways to accomplish both. In contrast to the classical strategies such as incorporating plasticizers or ceramic to prepare the silicon-based dielectric elastomers, here, blending an amino-complexed hybrid (polyethyleneimine (PEI)-Ag) with polydimethylsiloxane (PDMS) elastomer is reported as an alternative strategy to tailor the ɛr and Y. PEI-Ag not only exhibits excellent dielectric enhancement properties but also minimizes the PDMS crosslinking through amino-complexed reaction between PEI and Pt catalysts. The prepared dielectric elastomers have a ɛr of 7.2 @ 103 ​Hz and Y of 1.14 ​MPa, leading to an actuation strain of 22.27 ​% at 35 ​V/μm. Hence, incorporating such novel hybrids based on dual amino-complexed effect on both matrix and particles sufficiently promotes the actuated performance of dielectric elastomers.

Flexible and elastic thermal regulator for multimode intelligent temperature control

AbstractAs nonlinear thermal devices, thermal regulators can intelligently respond to temperature and control heat flow through changes in heat transfer capacities, which allows them to reduce energy consumption without external intervention. However, current thermal regulators generally based on high‐quality crystalline‐structure transitions are intrinsically rigid, which may cause structural damage and functional failure under mechanical strain; moreover, they are difficult to integrate into emerging soft electronic platforms. In this study, we develop a flexible, elastic thermal regulator based on the reversible thermally induced deformation of a liquid crystal elastomer/liquid metal (LCE/LM) composite foam. By adjusting the crosslinking densities, the LCE foam exhibits a high actuation strain of 121% with flexibility below the nematic–isotropic phase transition temperature (TNI) and hyperelasticity above TNI. The incorporation of LM results in a high thermal resistance switching ratio of 3.8 over a wide working temperature window of 60°C with good cycling stability. This feature originates from the synergistic effect of fragmentation and recombination of the internal LM network and lengthening and shortening of the bond line thickness. Furthermore, we fabricate a “grid window” utilizing photic‐thermal integrated thermal control, achieving a superior heat supply of 13.7°C at a light intensity of 180 mW/cm2 and a thermal protection of 43.4°C at 1200 mW/cm2. The proposed method meets the mechanical softness requirements of thermal regulator materials with multimode intelligent temperature control.

Effects of low and high frequency actuation on aerodynamic performance of a supercritical airfoil

The main objective of this study is to investigate the effects of low and high frequency actuation in improving the aerodynamic performance of the supercritical airfoil with the approach of using it in a high-lift or flight control device. For this purpose, a flow control numerical simulation is performed on a supercritical airfoil with NASA SC(2)-0714 cross section using a pulsed jet at the chord-based Reynolds number of 1 × 106. The pulsed jet actuation with different reduced frequencies of 0.2, 1, 1.2, 2.4, 4, 6, and 12 is implemented on the upper side of the airfoil surface upstream of the separation point of the uncontrolled case. The aerodynamic efficiency improvements are investigated by extracting the results of time-averaged and instantaneous aerodynamic forces for all cases. The study compares the flow streamline, Q-criterion contour, and surface pressure distribution to examine how the separated flow configuration over the airfoil responds to different actuation frequencies. The results indicate that pulsed jet actuation effectively postpones the flow separation. A comparison of the time-averaged aerodynamic coefficients at different actuation frequencies revealed that utilizing a low actuation frequency range maximizes lift, while a high frequency range minimizes drag. In addition, the aerodynamic efficiency of the supercritical airfoil improves across all controlled scenarios, with the optimal increase in aerodynamic efficiency of 28.62% achieved at an actuation frequency of F+ = 1.

Magnetic-field induced asymmetric hydrogel fibers for tough actuators with programmable deformation

Ingenious design of soft actuators with high mechanical performance, rapid actuation, and programmable deformation is necessary for their practical applications in the fields of artificial muscles, smart textiles, and soft robotics. Here we used a facile magnetic-field induction strategy to fabricate programmable actuators composed of tough hydrogel fibers. The anisotropic hydrogel fibers that consisted of dual physically cross-linked networks showed high tensile strength (28.9 MPa), while the asymmetric distribution of magnetic nanoparticles in hydrogel networks endowed the actuators with rapid bending velocity (3.2°·min−1·mm−1) in response to solvents. The pick-and-place manipulation of objects from ethanol to water were demonstrated by using the soft grippers composed of asymmetric hydrogel fibers. Furthermore, smart curtains that were woven by hydrogel fibers automatically rolled up or spread out in response to the change of ambient humidity. This work proved that tough hydrogel fibers fabricated by our magnetic-field induction strategy provided more possibilities in the field of soft actuators.

Thermal and fatigue endurance strain response in low temperature sintered 0.4PZN-0.6PZT ceramics for actuator applications

Piezo-ceramics with low sintering temperature (<1000 °C), enhanced strain (>0.1 %), low degree of hysteresis (<10 %), fatigue resistance (>106 cycles) with better thermal stability are extremely important characteristics for the development of high performance and cost-effective actuators. In this study, temperature (−50 to 250 °C) and fatigue (100 to 106) dependence of ferro/piezoelectric (P-E/S-E) characteristics of low temperature sintered (950 °C) (0.4[Pb(Zn1/3Nb2/3)O3-0.6Pb(Zr0.49Ti0.51)O3]) ceramics was investigated. A thermally stable strain response with a maximum of 0.17 % and degree of strain hysteresis (ηhys) of < 10 % was observed till 250 °C. The fatigue studies revealed a robust unipolar strain stability till 106 cycles even up to 200 °C. Interestingly, a very minimal strain asymmetry (γS) was observed only after 104 cycles till 200 °C, unlike PZT-5A, PIC151 and PMN-PT. This study demonstrates an exceptional thermal and fatigue resistant strain response even close to the Curie transition temperature (TC ∼ 280 °C) and suggests that the low temperature sintered 0.4PZN-0.6PZT ceramics could be a promising material, exclusively for high-precision actuator applications over a wide temperature range with a cost-effective solution.

The Frequency-Variable Rotor-Blade-Based Two-Degree-of-Freedom Actuation Principle for Linear and Rotary Motion.

Piezoelectric accurate actuation plays an important role in industrial applications. The intrinsic frequency of previous actuators is invariable. However, variable frequency can approach the range near the low-intrinsic-frequency and realize a high actuation capability. The frequency-variable linear and rotary motion (FVLRM) principle is proposed for rotor-blade-based two-degree-of-freedom driving. Inertial force is generated by frequency-variable piezoelectric oscillators (FVPO), the base frequency and vibration modes of which are adjustable by the changeable mass and position of the mass block. The variable-frequency principle of FVPO and the FVLRM are recognized and verified by the simulations and experiments, respectively. The experiments show that the FVLRM prototype moves the fastest when the mass block is placed at the farthest position and the prototype is at the second-order intrinsic frequencies of 42 Hz and 43 Hz, achieving a linear motion of 3.52 mm/s and a rotary motion of 286.9 mrad/s. The actuator adopts a lower operating frequency of less than 60 Hz and has the function of adjusting the natural frequency. It can achieve linear and rotational motion with a larger working stroke with 140 mm linear movement and 360° rotation.

Rapid and spatially programmed electrostatic actuation of anisotropic polymers

Liquid crystal elastomers (LCEs) are a fascinating class of anisotropic soft actuating materials that can respond to various stimuli. However, achieving both fast actuation and a high degree of freedom (DOF) in the LCE is one of the main challenges to overcome. In this study, we demonstrate rapid actuation (∼25 Hz) of LCEs driven by electrostatic force via direct charging. Notably, the end of the LCE film in our system is physically separated from the electrode, unlike conventional dielectric elastomer actuators, which allow a high DOF actuation when applying the DC or AC voltage in a spatially controlled manner. As a proof-of-concept, various functional actuators, including popup letters, a Kirigami-inspired spring, a dynamic segments device, a freeform oscillator, and a flapping motion of beetle, are successfully demonstrated. We envision our electrostatically actuating LCEs with sophisticatedly engineered electric fields in 1D, 2D, and 3D environments as a valuable platform for investigating the fundamental mechanics of electric field-driven soft actuators.

3D-Printed ferromagnetic Liquid Crystal Elastomer with Programmed Dual-Anisotropy And Multi-Responsiveness.

Liquid crystal elastomers (LCE) and magnetic soft materials are promising active materials in many emerging fields, such as soft robotics. Despite the high demand for developing active materials that combine the advantages of LCE and magnetic actuation, the lack of independent programming of the LCE nematic order and magnetization in a single material still hinders the desired multi-responsiveness. In this study, we developed a ferromagnetic LCE (magLCE) ink with nematic order and magnetization that can be independently programmed to be anisotropic, referred to as dual anisotropy, via a customized 3D printing platform. The magLCE ink was fabricated by dispersing ferromagnetic micro-particles in the LCE matrix, and a 3D printing platform was created by integrating a magnet with 3-DoF motion into an extrusion-based 3D printer. In addition to magnetic fields, magLCEs can also be actuated by heating sources (either environmental heating or photo-heating of the embedded ferromagnetic microparticles) with a high energy density and tunable actuation temperature. We demonstrated a programmed magLCE strip robot with enhanced adaptability to complex environments (different terrains, magnetic fields, and temperatures) using a multi-actuation strategy. The magLCE also has potential applications in mechanical memory, as demonstrated by the multi-stable mechanical metastructure array with remote writability and stable memory. This article is protected by copyright. All rights reserved.

Dielectric anomaly in Bi3Ti1-x(Y0.5Sb0.5) xNbO9 piezoceramics with high Curie temperature

Bismuth layered material stand out from other piezoelectric materials due to their high Curie temperature (Tc) and are often used in high temperature piezoelectric actuators and capacitors. However, its low piezoelectric coefficient (d33) and dielectric constants (ε′) limit the scope of application of this material. The Bi3Ti0.99 (Y0.5Sb0.5) 0.01NbO9 (BTN-1YSb) ceramics by solid state sintering method show improved d33 (8.1 pC/N), dielectric constants (ε′ ∼2051), temperature stability (d33＞8 pC/N at 800 °C) and mechanical quality factor (Qm ∼ 1834). After Rietveld refinement, it was found that the oxygen element contributed the most to the spontaneous polarization (Ps) enhancement of the piezoelectric material. In addition, three dielectric anomalous peaks are observed for the first time in BTNO-4YSb BTN-3YSb ceramics, which is due to the interaction of point defects with domain walls in a wide temperature range. This advantage can be maximized by tuning the dielectric anomaly peak to provide a more stable d33 at high temperatures. This study analyzes that the contribution of each ion to the piezoelectric properties of BTN-based ceramics and provides a good example for the study of dielectric peaks.

Comparative analysis of process-induced strain glass states in austenitic and martensitic NiTi shape memory alloy plates

Strain glass alloys (SGAs) are metallic alloys with glassy martensitic nanodomains within a crystalline material that occur from compositionally or processing-induced strain. SGAs originate from shape memory alloys (SMAs) and exhibit similar shape memory properties and high actuation densities. The transition from SMA to SGA is relatively unexplored, and although there are similarities to amorphous SMAs and cold-worked SMAs, SGAs should be distinguished as a separate grouping. The transition occurs by interrupting the long-range martensitic order, which in turn disrupts the martensitic transformation, resulting in short-range martensitic order. A glassy martensitic phase is produced that exhibits enhanced structural and load-bearing abilities, functional stresses, and recoverability. In this study, the transformation from SMA to SGA is explored in two common commercially available SMAs, Ni49.5Ti50.5 and Ni50.8Ti49.2 (at. %), to compare martensitic versus austenitic SGAs, respectively. SMA plates were cold worked in 5% increments until a strain glass transition occurred. Characterizations of the samples at various stages of cold work were examined via differential scanning calorimetry (DSC), Vickers hardness, transmission electron microscopy (TEM), and synchrotron radiation X-ray diffraction (SR-XRD). Some prominent characteristics between the two plates, such as enthalpy peaks, twin size reduction, and crystallographic structure, were examined and compared to improve the understanding of the SMA to SGA transition.

Adaptive energy harvesting from low-level ambient vibrations

Harvesting energy from ambient mechanical vibrations is an enabling technology with profound societal impacts. However, existing methods suffer from two major technical deficiencies: the weak coupling between the harvester and the vibrating source and the low energy transduction efficiency. Here we show an adaptive approach can overcome these challenges, leading to improvements by orders of magnitude. Using a piezoelectric device, we demonstrate that a conservative actuation force can block energy from flowing back to the vibrating source, thereby increasing the coupling strength and increasing the transduction efficiency significantly. Using low actuation forces, the adaptive approach can extract almost two orders of magnitude more power than the traditional approach from a multi-frequency vibration. The improvement can increase to three orders of magnitude when moderate actuation force is used. If materials that can withstand a high actuation voltage are available, the adaptive approach has the potential to surpass the theoretical performance ceiling of the traditional approach, improving the upper-bound performance by over 100 times and creating a significant opportunity for the technology to advance.

Thermo-Pneumatic Artificial Muscle: Air-Based Thermo-Pneumatic Artificial Muscles for Pumpless Pneumatic Actuation.

To make robots more human-like and safer to use around humans, artificial muscles exhibiting compliance have gained significant attention from researchers. However, despite having excellent performance, pneumatic artificial muscles (PAMs) have failed to gain significant traction in commercial mobile applications due to their requirement to be tethered to a pneumatic source. This study presents a thermo-PAM called Thermo-PAM that relies on heating of a volume of air to produce a deformation. This allows for pneumatic actuation using only an electrical power source and thus enables pumpless pneumatic actuation. The actuator uses a high ratio between the heating volume and the deformable volume to produce a high actuation force throughout its entire motion and can produce either contractile or extension motions. The controllability of the actuator was demonstrated as well as its ability to handle heavy payloads. Moreover, it is possible to rely on either positive or negative pressure actuation modes where the positive pressure actuation mode actuates when heated and the negative pressure actuation mode relaxes when heated. The ability to use Thermo-PAMs for different modes of actuation with different operation methods makes the proposed actuator highly versatile and demonstrates its potential for advanced pumpless robotic applications.

Soft Robotic Finger with Energy-Coupled Quadrastability.

The performance of the human finger is a significant inspiration for designing soft robotic fingers that can achieve high speed and high force or perform delicate and complex tasks. Existing soft grippers and actuators can be excellent in specific capabilities. However, it is still challenging for them to meet an all-around performance as the human finger, characterized by high actuation speed, wide grasping range, sensing ability, and gentle and high-load grasping capability. The proposed tendon pulley quadrastable (TPQ) finger has combined these qualities in the conducted gripping tasks. A pair of elastic tendons is utilized as the sole energy reservoir to create a novel energy distribution pattern: energy-coupled quadrastability. An energy model is built to analyze and predict the behaviors of the TPQ finger. Mechanical instability is utilized to enhance the actuation speed. The proposed soft lever mechanism endows the TPQ finger with sensing ability. The energy barrier adjusting plates control the energy barrier, adjusting the sensitivity of both active and passive actuation mechanisms. The transition of four stable states forms preplanned trajectories that are applied to create multiple grasping manners. Experiments show that it can respond to stimuli and finish a grasping task in merely 31 ms, and its payload can reach 33.25 kg. At the same time, it can also handle fragile objects such as a piece of rose and grasp a wide range of objects ranging from a thin nut (3.3 mm in height) or a thin card (0.76 mm thick) to a football (220 mm).

Integration of Multifunctional Epitaxial (Magnetic) Shape Memory Films in Silicon Microtechnology

AbstractMagnetic shape memory alloys exhibit various multifunctional properties, which range from high stroke actuation and magnetocaloric refrigeration to thermomagnetic energy harvesting. Most of these applications benefit from miniaturization and a single crystalline state. Epitaxial film growth is so far only possible on some oxidic substrates, but they are expensive and incompatible with standard microsystem technologies. Here, epitaxial growth of Ni–Mn–based Heusler alloys with single crystal‐like properties on silicon substrates is demonstrated by using a SrTiO3 buffer. It is shown that this allows using standard microfabrication technologies to prepare partly freestanding patterns. This approach is versatile, as its applicability for the NiTi shape memory alloy is demonstrated and spintronic and thermoelectric Heusler alloys are discussed. This paves the way for integrating additional multifunctional effects into state‐of‐the‐art microelectronic and micromechanical technology, which is based on silicon.

Electronic Implementation of High Bandwidth Linear Hydraulic Actuator for Legged Robot’s Applications

Electronic Implementation of High Bandwidth Linear Hydraulic Actuator for Legged Robot’s Applications

Optimized Strain Response in (Co0.5Nb0.5)4+-Doped 76Bi0.5Na0.5TiO3-24SrTiO3 Relaxors

High strain with low hysteresis is crucial for commercial applications in high precision actuators. However, the clear conflict between the high strain and low hysteresis in BNT-based ceramics has long been an obstacle to actual precise actuating or positioning applications. To obtain piezoceramics with high strain and low hysteresis, it is necessary to enhance the electrostrictive effect and develop an ergodic relaxor (ER) and nonergodic relaxor (NR) phase boundary under ambient conditions. In this work, (Co0.5Nb0.5)4+ doped 76Bi0.5Na0.5TiO3-24SrTiO3 (BNST24) relaxors were fabricated using the conventional solid state reaction route. X-ray diffraction patterns revealed the B-site substitution in BNST24 ceramics. By adjusting the (Co0.5Nb0.5)4+ doping in BNST24, we effectively tuned the TNR-ER and Td close to ambient temperature, which contributed to the development of the ergodic relaxor phase and enhanced the electrostrictive effect at ambient temperature. The I-P-E loops and bipolar strain curves verified the gradual evolution from NR to ER states, while the enhanced electrostrictive effect was verified by the nearly linear S-P2 curves and improved electrostrictive coefficient of the BNST24-xCN relaxors. An enhanced strain of 0.34% (d*33 = 483 pm/V) with low hysteresis of 8.9% was simultaneously achieved in the BNST24-0.02CN relaxors. The enhanced strain was mainly attributed to the proximity effect at the ER and NR phase boundary of BNST24-0.02CN, while the improved electrostrictive effect contributed to the reduced strain hysteresis. Our work demonstrates an effective strategy for balancing the paradox of high strain and low hysteresis in piezoceramics.

Multifunctional Magnetoelectric Sensing and Bending Actuator Response of Polymer-Based Hybrid Materials with Magnetic Ionic Liquids.

With the evolution of the digital society, the demand for miniaturized multifunctional devices has been increasing, particularly for sensors and actuators. These technological translators allow successful interaction between the physical and digital worlds. In particular, the development of smart materials with magnetoelectric (ME) properties, capable of wirelessly generating electrical signals in response to external magnetic fields, represents a suitable approach for the development of magnetic field sensors and actuators due to their ME coupling, flexibility, robustness and easy fabrication, compatible with additive manufacturing technologies. This work demonstrates the suitability of magnetoelectric (ME) responsive materials based on the magnetic ionic liquid (MIL) 1-butyl-3-methylimidazolium tetrachloroferrate ([Bmim][FeCl4]) and the polymer poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE) for magnetic sensing and actuation device development. The developed sensor works in the AC magnetic field and has frequency-dependent sensitivity. The materials show voltage responses in the mV range, suitable for the development of magnetic field sensors with a highest sensitivity (s) of 76 mV·Oe-1. The high ME response (maximum ME voltage coefficient of 15 V·cm-1·Oe-1) and magnetic bending actuation (2.1 mm) capability are explained by the magnetoionic (MI) interaction and the morphology of the composites.

Photocontrollable Elongation Actuation of Liquid Crystal Elastomer Films with Well-Defined Crease Structures.

Although liquid crystal elastomers (LCEs) have demonstrated various applications in artificial muscles and soft robotics, their inherent flexibility and orientation-dependent forces limit their functions. For instance, LCEs can sustain a high actuation force when they contract but cannot elongate to drive loads with large displacements. In this study, it is demonstrated that photocontrollable elongation actuation with a large strain can be achieved in polydomain LCEs by programming the crease structures in a well-defined order to couple the actuation forces. Efficient photoactuation without overheating-induced damage to the materials is favored, based on the well-designed photosensitive molecular switch crosslinker via the synergy of photochemical and photothermal effects. The LCE actuator can jack up heavy loads, elongate freely, and contract back to manipulate distant objects. Theoretical analysis based on a finite element simulation of the deformation energy during the actuation process reveals a trade-off between the abilities of jacking-up and withstanding load. More importantly, this study simplifies the design of a single material with functions inherent only in other soft robotic devices based on the assembly of multiplemodules, thus providing a design strategy for surpassing instinctive properties of conventional soft materials to expand the functions of soft robotics.

High-precision dynamic torque control of high stiffness actuator for humanoids

The high stiffness actuator (HSA), applied to each joint of an electrical driven humanoid robot, can directly affect the motion performance of the torque-controlled humanoid robots. For high control performance of HSA, a high-precision dynamic torque control (HDTC) is proposed. The HDTC consists of two phases: (1) A novel dynamic current control is used to linearize high stiffness actuator torque control system, which can estimate and compensate the nonlinear coupling parts; (2) An enhanced internal model control is designed to ensure high tracking accuracy in the system containing noisy torque signal and even numerical differentiation signals. Benefitting from dynamic current control and the enhanced internal model control, the proposed HDTC is accurate and adaptable. Finally, the superiority of the HDTC is verified with comparative experiments.

Design, fabrication and experiments of a hydraulic active-passive hybrid prosthesis knee.

Due to low friction, passive mechanical prostheses move compliantly followed by the stump and are used widely. Advanced semi-active prostheses can both move passively like passive prostheses and provide active torque under specific conditions. However, the current mechanical-hydraulic coupling driven semi-active prostheses, in order to meet the low passive friction requirements with a low active transmission ratio, lead to a significant problem of insufficient active torque. A hybrid active and passive prosthesis was developed to solve the incompatibility problem of low passive friction and high active driving torque of semi-active prostheses. The mechanical structure and control strategy of the prosthesis were demonstrated. The performance of the prosthesis was tested by bench and human tests. Passive subsystem damping adjustment ranges from 0.4 N⋅(mm/s)-1 to 300 N⋅(mm/s)-1. The switching time between the damping and the active subsystem is 32 ± 2 ms. The continuous active torque output is more than 24 Nm. In level walking, the peak torque is about 28 Nm. The proposed active-passive hybrid hydraulic prosthesis could satisfy both low passive friction and high active actuation.