Actuation Modes Research Articles

Knotted Artificial Muscles for Bio-Mimetic Actuation under Deepwater.

Muscles featuring high frequency and high stroke linear actuation are essential for animals to achieve superior maneuverability, agility, and environmental adaptability. Artificial muscles are yet to match their biological counterparts, due to inferior actuation speed, magnitude, mode, or adaptability. Inspired by the hierarchical structure of natural muscles, artificial muscles are created that are powerful, responsive, robust, and adaptable. The artificial muscles consist of knots braided from 3D printed liquid crystal elastomer fibers and thin heating threads. The unique hierarchical, braided knot structure offers amplified linear stroke, force rate, and damage-tolerance, as verified by both numerical simulations and experiments. In particular, the square knotted artificial muscle shows reliable cycles of actuation at 1Hz in 3000m depth underwater. Potential application is demonstrated by propelling a model boat. Looking ahead, the knotted artificial muscles can empower novel biomedical devices and soft robots to explore various environments, from inside human body to the mysterious deepsea.

Design, modeling, and analysis of a new XYθ piezoelectric microstage featuring high amplification ratios and multiple actuation modes

Design, modeling, and analysis of a new XYθ piezoelectric microstage featuring high amplification ratios and multiple actuation modes

Ultra-Large Stress and Strain Polymer Nanocomposite Actuators Incorporating a Mutually-Interpenetrated, Collective-Deformation Carbon Nanotube Network.

Stimulus-responsive polymer-based actuators are extensively studied, with the challenging goal of achieving comprehensive performance metrics that include large output stress and strain, fast response, and versatile actuation modes. The design and fabrication of nanocomposites offer a promising route to integrate the advantages of both polymers and nanoscale fillers, thus ensuring superior performance. Here, it is started from a three-dimensional (3D) porous sponge to fabricate a mutually interpenetrated nanocomposite, in which the embedded carbon nanotube (CNT) network undergoes collective deformation with the shape memory polymer (SMP) matrix during large-degree stretching and releasing, increases junction density with polymer chains and enhances molecular orientation. These features result in substantial improvement of the overall mechanical properties and during thermally actuated contraction, the bulk SMP/CNT composites exhibit output stresses up to 19.5 ± 0.97MPa and strains up to 69%, accompanied by a rapid response and high energy density, exceeding the majority of recent reports. Furthermore, electrical actuation is also demonstrated via uniform Joule heating across the self-percolated CNT network. Applications such as low-temperature thermal actuated vascular stent and wound dressing are explored. These findings lay out a universal blueprint for developing robust and highly deformable SMP/CNT nanocomposite actuators with broad potential applications.

Active‐Textile Yarns and Embroidery Enabled by Wet‐Spun Liquid Crystalline Elastomer Filaments

AbstractLiquid crystal elastomers (LCEs) are promising candidates for creating adaptive textile‐based devices that can actively and reversibly respond to the environment for sensing and communication. Despite recent advances in scalable manufacturing of LCE filaments for textile engineering, the actuation modes of various LCE filaments focus on contractual deformations. In this study, manufacture of polydomain LCE filaments with potential scalability by wet‐spinning is studied, followed by mechanical exploitation to program liquid crystal mesogen alignments, demonstrating both contractual and twisting actuation profiles. By plying these LCE filaments into yarns with different twist concentrations, yarn actuation, and mechanical performance is tuned. Yarns plied at 4 twists per cm can generate up to a seven‐fold increase in elastic modulus while maintaining 90% of actuation strain performance from their native filament. The contractual and twisting LCE filaments are then embroidered with varying stitch types to spatially program complex 2D‐to‐3D transformations in “inactive” fabrics. It is shown that a running stitch can actuate up to 15% in strain and create angular displacements in fabric with twisted mesogen alignments. It is envisioned that the wet‐spun polydomain LCE filaments for diverse plied yarn production together with textile engineering will open new opportunities to design smart textiles and soft robotics.

Optimization of piezoelectric device with both mechanical and electrical properties for power supply of road sensors

Collecting and converting renewable energy from the road environment relieves pressure on energy supply for road-based sensing and monitoring, and simplify the process of road grid installation. Aiming at the characteristic of mechanical vibration energy collection, the internal structure of the piezoelectric device is optimized. The dowel bar structure is optimized by comparing the output power and stress distribution characteristics, while the actuation mode is selected based on the measured electrical output level and output stability. Then, based on the limit distance of single and dynamic loading, the range of actuation distance under different conditions is clarified. Finally, the electrical performance and application of energy harvester with optimized internal structure are systematically evaluated. The results indicate that the force-electric properties of the energy harvester are superior under the action of the cylinder, the actuation mode of the energy harvester driven by the dowel bar is conducive to improving the electrical performance. The upper limit of actuation distance under high traffic conditions is 1.3 mm. Under long-term high-frequency condition, the power density of the energy harvester can reach 14,726.67 W/m3, and the voltage has almost no attenuation after 100,000 continuous loads. The proposed internal structure improves the electrical performance and durability of the energy harvester, which is conducive to the development of self-powered energy supply for road sensing technology.

An improved equivalent circuit model of a V-shape single-mode linear ultrasonic motor with new actuation mode

Single-mode linear ultrasonic motors (SMLUMs) have the advantages of excellent accuracy, long travel distance, single vibration mode and simple driving scheme, which have been applied in precision positioning and micro/nano manipulation actuators. However, it is still challenging to accurately and efficiently analyze such motors due to their complicated electro-mechanical coupling behaviors under contact-based operating conditions. This paper proposed an improved equivalent circuit model for a single-mode linear ultrasonic motor considering the real contact-based operating conditions, where a new actuation mode of the V-shape transducer is adopted. The electro-mechanical coupling characteristics of the stator under contact-based boundary condition is modeled by a modified admittance-type equivalent circuit, where the variable contact stiffness and loss are characterized between the stator and the mover. The friction drive mechanism is modeled by a thyristor rectifying circuit to characterize the intermittent actuation characteristics, and the nonlinear relationship between the motor characteristics and the contact-based operating conditions is initially characterized from the circuit viewpoint. The merits and the applications of the circuit-based model are exemplified by parameter identification and modification, losses segregation, admittance characteristics analysis and output and control characteristics evaluation for such SMLUMs.

Reprogramming Photoresponsive Liquid Crystalline Elastomer via Force-Directed Evaporation.

Incorporating photothermal agents into thermoresponsive liquid crystalline elastomers (LCEs) offers remote and spatio-temporal control in actuation. Typically, both the light responsiveness and actuation behaviors are fixed since the agent doping and mesogen alignment are conducted before network formation. Here, we report an approach that enables programming photoresponsive LCEs after synthesis via force-directed evaporation. Different photothermal agents can be doped or removed by swelling the fully cross-linked LCEs in a specific solution, achieving the introduction and erasing of the photoresponsiveness. Moreover, the network swelling deletes the registered alignment, which allows for redefining the molecular order via re-evaporating the solvent with force imposed. This "one stone, two birds" strategy paves the way to simultaneously program/reprogram the actuation mode and responsiveness of LCEs, even in a spatio-selective manner to achieve complex actuations. Our approach is expandable to three-dimensional (3D) printed LCEs to access geometrically sophisticated shape-changing.

Plasma Actuator Separation Control Investigated with Spectral Proper Orthogonal Decomposition

A single dielectric-barrier discharge plasma actuator is an active flow control device that imparts momentum to the fluid through ion acceleration using electromagnetic forces and has been used to suppress flow separation. This paper studies flow over an airfoil and how adding a single dielectric-barrier discharge actuator influences flow characteristics through numerical modeling. Using the spectral proper orthogonal decomposition and large-eddy simulation, flow instabilities are analyzed at their different temporal and spatial scales in the wake region. This study aims to explore the viability of spectral proper orthogonal decomposition for separation control and correlate the decomposed flow modes to the different actuation modes.

Scaling effects of manufacturing processes and actuation sources on control of remotely powered micro actuators

Over the past decade, remotely powered micro actuators have gained increased attention for biomedical and environmental remediation applications, owing to their ability to access confined regions and the nonintrusive nature of control. Recent studies focus on improving the functionality and versatility of micro actuators through the development of new fabrication and actuation techniques. However, there is a possibility that a limited understanding of the scaling impact of various physical principles governing design and control has affected the successful implementation of such devices in practical scenarios. Thus, the main focus of this review is to evaluate the most widely utilized manufacturing methods and remote actuation sources in light of various characteristics such as resolution, productivity, shape complexity, actuation speed, actuation mode, operating medium, and so on. State-of-the-art developments in each type of manufacturing and actuation are introduced and delineated. Finally, the limitations of current devices are reviewed, and the future direction to enable the full potential of this field is provided.

Magneto‐Responsive Bistable Structures with Rate‐Dependent Actuation Modes

AbstractStructural instabilities can be used to provide rapid responses activated by mechanical force or displacement thresholds. The emergence of responsive materials has opened the door for adapting such structural instabilities to actuators that will abruptly deform guided by external stimuli. However, fast configurational transitions between equilibrium states imply important viscoelastic roles at the material level that inevitably scale up to the structural level. A comprehensive understanding of viscoelastic effects is provided on bistable structural transitions combining a new experimental perspective and a thorough modeling analysis. The insights from these results are here translated to magneto‐responsive bistable structures offering a route‐map to design effective actuation conditions. The bistable transition functionally depends on the combination of magnetic field amplitude and application rate. The understanding of the viscoelastic and magneto‐mechanical coupling provides efficient actuation via temporal magnetic pulses, removing the need of generating continued magnetic fields. Finally, these insights are combined to develop a responsive structure whose transient and steady bistable transitions can be modulated by the application rate of external magnetic stimuli.

Moisture‐Driven Cellulose Actuators with Directional Motion and Programmable Shapes

The hygroscopic motion of plants has inspired the development of moisture‐activated soft actuators. These actuators driven by ambient moisture sources are of great research interest in robotics and self‐regulating textiles. However, these actuators often have slow motion and can only perform bending and twisting motions. Herein, a cellulose film‐based fast‐morphing and motion‐programmable soft actuator is presented that can generate caterpillar‐like movement. The cellophane films reported here bend almost instantaneously under changing humidity, with a large bending curvature, high repeatability, and negligible hysteresis. Different actuation modes are studied using both coated and uncoated cellophane films. The uncoated cellophane film can continuously move on a moist substrate through autonomous bending–rolling–flipping (or oscillating) cycles. A facile strategy is used here to control the rolling direction and facilitate the flipping motion by offsetting its center of gravity during deformation by adding appropriate weights on the end of the actuator. The coated cellophane film is used to fabricate motion‐programmable actuators through heat‐laminating. Several actuator structures are designed and fabricated and their diverse moisture‐induced motions are demonstrated.

Multimodal Soft Robotic Actuation and Locomotion.

Diverse and adaptable modes of complex motion observed at different scales in living creatures are challenging to reproduce in robotic systems. Achieving dexterous movement in conventional robots can be difficult due to the many limitations of applying rigid materials. Robots based on soft materials are inherently deformable, compliant, adaptable, and adjustable, making soft robotics conducive to creating machines with complicated actuation and motion gaits. This review examines the mechanisms and modalities of actuation deformation in materials that respond to various stimuli. Then, strategies based on composite materials are considered to build toward actuators that combine multiple actuation modes for sophisticated movements. Examples across literature illustrate the development of soft actuators as free-moving, entirely soft-bodied robots with multiple locomotion gaits via careful manipulation of external stimuli. The review further highlights how the application of soft functional materials into robots with rigid components further enhances their locomotive abilities. Finally, taking advantage of the shape-morphing properties of soft materials, reconfigurable soft robots have shown the capacity for adaptive gaits that enable transition across environments with different locomotive modes for optimal efficiency. Overall, soft materials enable varied multimodal motion in actuators and robots, positioning soft robotics to make real-world applications for intricate and challenging tasks.

A Dynamic Modeling Method for Soft Pneumatic Robotic Arms Considering Both Geometric Nonlinearity and Visco-Hyperelasticity

This work proposes a new dynamic modeling approach that integrates the principle of virtual power and a spring–damper–fluid equivalent method. It is able to simultaneously consider the geometric and material nonlinearity including hyperelasticity and viscoelasticity of the soft robotic arm. Meanwhile, the nonuniform deformation of the soft arm wall can be introduced into the model based on the equivalent model. A general prototype of soft robotic arms is fabricated and validation experiments of three pneumatic actuation modes are carried out. A maximum position error of 3.64[Formula: see text]mm at the end of the soft arm is obtained with an eight-segment theoretical model for the 280[Formula: see text]mm long and 30[Formula: see text]mm thick prototype in an approximate step actuation test with a maximum pneumatic pressure of 11.5[Formula: see text]kPa. The comparisons between the theoretical prediction and experimental results demonstrate a high accuracy of the proposed modeling method. Besides, simulations of dynamic motions under in-plane and out-of-plane actuation are carried out respectively, illustrating that the proposed method has the ability to describe a variety of actuation forms. The proposed dynamic modeling method provides a new way for modeling the soft robotic arms and has guiding significance for the design and control of soft robotic arms.

Repeatedly Programmable Liquid Crystal Dielectric Elastomer with Multimodal Actuation.

Dielectric elastomers (DEs) are actuatable under an electric field, whose large strain and fast response speed compare favorably with natural muscles. However, the actuation of DE-based devices is generally limited to a single mode and cannot be reconfigured after fabrication, which pales in comparison to biological counterparts given the ability to alter actuation modes according to external conditions. To address this, liquid crystal dielectric elastomers (LC-DEs) that can alter the dielectric actuation modes based on the thermally triggered shape-changing are prepared. Specifically, the two shapes through the LC phase transition possess different bending stiffness, which leads to distinct actuation modes after an electric field is applied. Moreover, the two shapes can be individually programmed/reprogrammed, that is, the one before the transition is regulated through force-directed solvent evaporation and the one after the transition is via bond exchange-enabled stress relaxation. As such, the multimodal dielectric actuation behaviors upon temperature change can be readily diversified. Meanwhile, the space charge mechanism endows LC-DEs with the significantly reduced driving e-field (8 V µm-1) and bidirectional actuation manners. It is believed this unique adaptivity in the actuation modes under a low electric field shall offer versatile designs for practical soft robots.

Smart electro-magneto-viscoelastomer minimum energy structures with particle-reinforcements: Theoretical equilibrium and nonlinear dynamics of actuated configurations

Soft transduction technology is rapidly adopting soft active elastomer-based minimum energy structures because of their distinctive programmable shape-morphing characteristics. For effective device design, an understanding of the nonlinear dynamic behavior is crucial as they often experience time-dependent motion while operating. Moreover, there has been an increasing scientific interest in enhancing the actuation performance of soft active elastomers by imparting particle reinforcements. This article provides a theoretical framework for investigating the nonlinear dynamics of smart composite elastomer-based minimum energy structures (SCEMES) with the provision of non-aligned electric and magnetic fields, leading to an actively programmable pre-stretch paradigm. Unlike conventional actuators, the proposed SCEMES is made up of a polymer that has electro-magnetic properties and is filled with appropriate fillers with specific volume fractions. An electromagneto-viscoelastic model is developed here to predict actuator behavior and investigate the effects of particle reinforcement on equilibrium and actuated configurations. Besides strengthening the polymer, particle reinforcement is observed to enhance the equilibrium angle achieved by the structure with enhanced functionality. The proposed nonlinear dynamic model is extended to investigate a number of critically influential parameters, including shear modulus ratio of fiber to matrix, frame bending stiffness, membrane pre-stretching, and electro-magnetic loading with time-dependent DC and AC modes of actuation. The results reveal that the combined electro-magnetic actuation enhances the actuation range significantly. The attained tip angle of the actuator increases appreciably when the magnetic and electric fields are applied mutually perpendicular to each other, indicating that the direction of applied magnetic field governs the attained actuated configuration. Further, particle reinforcement enrichments result in a depletion in oscillation amplitudes and an increase in excitation frequencies under the AC actuation mode. The efficient semi-analytical framework presented here would be crucial in developing new actuators, smart devices and soft robots for a variety of advanced engineering and medical applications.

Rotini-like MXene@LCE Actuator with Diverse and Programmable Actuation Based on Dual-mode Synergy.

Liquid crystalline elastomer (LCE) exhibits muscle-like actuation upon order-disturbed stimulus, offering ample room for designing soft robotic systems. Multimodal LCE is demonstrated to unleash the potential to perform multitasks. However, each actuation mode is typically isolated. In contrast, coordination between different actuation modes based on an MXene-doped LCE is realized, whose actuation can be triggered either by directly heating/cooling or using near-infrared light due to the photo-thermal effect of MXene. As such, the two activation modes (heat and light) not only can work individually to offer stable actuation under different conditions but also can collaborate synergistically to generate more intelligent motions, such as achieving the brake and turn of an autonomous rolling. The principle therefore can diversify the design principles for multifunctional soft actuators and robotics.

Deformation-controlled and ultrasensitive polyimide/paraffin wax/carbon nanotube composite NIR-responsive photoactuators

Light-responsive actuators have become increasingly popular in various fields such as soft robotics, biomedical devices, and photosensitive electronic devices due to their remote wireless operation and high deformation efficiency. However, controlling actuator deformation efficiency and modes remains a significant challenge. Herein, a new 3D printed polyimide (PI)/paraffin wax (PW)/carbon nanotube (CNT) NIR-responsive photoactuators with controlled deformation mode and ultrasensitive light response has been proposed. The process involves printing a CNT slurry according to a predetermined path, followed by lamination with PW and PI film to create PI/PW/CNT (PPC) NIR responsive photoactuators. Then, the effects of the CNTs pattern (line width and line spacing) on the deformation efficiency were studied and optimized. Upon optimization, the deformation time can be reduced to 3 s and the deformation angle can be raised to 70°. Moreover, the PPC actuator is highly sensitive to temperature and can be deformed within a temperature difference of about 2–3 °C. Finally, various PPC photoactuators including Flower-shape and soft mechanical hand have been prepared to present the different deformation forms. Overall, this work presents a new approach to researching multifunctional NIR-responsive photoactuators with adjustable deformation structures.

Bridging two insect flight modes in evolution, physiology and robophysics

Since taking flight, insects have undergone repeated evolutionary transitions between two seemingly distinct flight modes1–3. Some insects neurally activate their muscles synchronously with each wingstroke. However, many insects have achieved wingbeat frequencies beyond the speed limit of typical neuromuscular systems by evolving flight muscles that are asynchronous with neural activation and activate in response to mechanical stretch2–8. These modes reflect the two fundamental ways of generating rhythmic movement: time-periodic forcing versus emergent oscillations from self-excitation8–10. How repeated evolutionary transitions have occurred and what governs the switching between these distinct modes remain unknown. Here we find that, despite widespread asynchronous actuation in insects across the phylogeny3,6, asynchrony probably evolved only once at the order level, with many reversions to the ancestral, synchronous mode. A synchronous moth species, evolved from an asynchronous ancestor, still preserves the stretch-activated muscle physiology. Numerical and robophysical analyses of a unified biophysical framework reveal that rather than a dichotomy, these two modes are two regimes of the same dynamics. Insects can transition between flight modes across a bridge in physiological parameter space. Finally, we integrate these two actuation modes into an insect-scale robot11–13 that enables transitions between modes and unlocks a new self-excited wingstroke strategy for engineered flight. Together, this framework accounts for repeated transitions in insect flight evolution and shows how flight modes can flip with changes in physiological parameters.

High-Precision Tip Tracking of a Flexible Link Manipulator Using Two-Time Scale Adaptive Robust Control

A flexible link manipulator (FLM) has advantages of greater payload-to-manipulator-weight ratio, safer operation, and lower energy consumption compared with the rigid manipulator, which has promising demands in various industrial and aerospace applications. However, the internal dynamics of the system is easy to be unstable due to its nonminimum phase characteristics, and there exists severe parametric uncertainties and uncertain nonlinearities in its dynamics, which has brought many difficulties in the precise tip tracking control and effective vibration suppression. In this article, the entire mathematical model of the FLM is established with assumed mode method and actuator dynamics. Then, the system is decomposed into a slow subsystem and a fast subsystem through introducing an adjustable time-scale factor according to a new output redefined dynamics with uncertainties from truncated vibration modes and unknown disturbances of system. A two-time scale adaptive robust control (TTSARC) scheme, which consists of an adaptive robust control for the slow subsystem and a state feedback control for the fast subsystem, is proposed to effectively handle parametric uncertainties and uncertain nonlinearities as well as improve behavior of internal dynamics. Moreover, the clear connection of achievable performances and control parameters based on the stability analysis of the entire system is addressed. The experimental results indicate that precise tip tracking with small link deflection for the FLM working on different conditions can be achieved with the proposed TTSARC.

Experimental investigation of expansive bending pipe flow separation control using a surface dielectric barrier discharge plasma actuator.

Adverse pressure gradients can cause severe flow separation within typical S-shaped inlets. This results in a total pressure distortion at the aerodynamic interface plane (AIP). The expansive bending pipe, where flow separation also occurs due to the adverse pressure gradient, is the basis for investigations into S-shaped inlets. In this study, surface dielectric barrier discharge (SDBD) plasma actuators are used to moderate the total pressure distortion in the AIP of an expansive bending pipe under a 10 m/s incoming flow. Also, the influences of actuation voltage amplitude and pulsed frequency on the total pressure distortion of the AIP are investigated under two plasma actuation modes, nanosecond pulsed SDBD and alternating current (AC) SDBD. Under optimal actuation parameters, the nanosecond pulsed SDBD and the AC-SDBD can reduce the distortion index by 14.93% and 32.22%, respectively. The results demonstrate the effectiveness of SDBD plasma actuators in suppressing flow separation within expansive bending pipes.