Ability Of Actuator Research Articles

Sequential Multimodal Morphing of Single-Input Pneu-Nets.

Soft actuators provide an attractive means for locomotion, gripping, and deployment of those machines and robots used in biomedicine, wearable electronics, automated manufacturing, etc. In this study, we focus on the shape-morphing ability of soft actuators made of pneumatic networks (pneu-nets), which are easy to fabricate with inexpensive elastomers and to drive with air pressure. As a conventional pneumatic network system morphs into a single designated state, achieving multimodal morphing has required multiple air inputs, channels, and chambers, making the system highly complex and hard to control. In this study, we develop a pneu-net system that can change its shape into multiple forms as a single input pressure increases. We achieve this single-input and multimorphing by combining pneu-net modules of different materials and geometry, while harnessing the strain-hardening characteristics of elastomers to prevent overinflation. Using theoretical models, we not only predict the shape evolution of pneu-nets with pressure change but also design pneu-nets to sequentially bend, stretch, and twist at distinct pressure points. We show that our design strategy enables a single device to carry out multiple functions, such as grabbing-turning a light bulb and holding-lifting a jar.

An all-in-one graphene-based ionic actuator with fast switching response

Graphene, as a typical two-dimensional material is widely recognized for its excellent performance to application in many fields such as smart actuation systems. Here, an all-in-one graphene-based smart actuator has been developed for the first time. The graphene oxide film containing with ionic liquid are reduced on both sides via laser writing method. The smart actuator exhibits a promising actuation ability triggered by a low operation voltage of 0.8 V and delivers a deformation in fast switching response (10 Hz for one cycle) and excellent actuation stability. It means the new integrated graphene-based actuator has the potential for practical applications.

Soft actuators based on piezoelectric composites for nanoscale self-bending

Nano/microscale objects would be far less damaged by soft actuators than rigid actuators in the mechanical nano/micromanipulation, but the precision of most soft actuators cannot meet the requirements. In this work, a kind of soft actuators which can realize nanoscale self-bending are developed on the basis of lead zirconate titanate (PZT)/shape memory polyurethane (SMPU) composites. The self-bending ability is the result of the weak polarization electric fields produced by the combination of the microstructures of particulate composites and the fringe effect of electric fields. However, unlike common piezoelectric actuators, strong polarization electric fields would weaken the actuation ability (self-bending ability). The PZT/SMPU actuators are able to generate nanoscale self-bending displacements with the maximum error of ± 8 nm in a common condition without controlling any environmental parameter. This work provides a helpful reference for the design of soft self-bending actuators based on piezoelectric particulate composites.

Light-driven soft climbing robot based on negative pressure adsorption

Many organisms rely on a dynamic attachment mechanism to climb surfaces. Inspired by these organisms, researchers have developed soft climbing robots. Despite their rapid development in recent times, such robots have restricted application in complex environments, such as the lack of remote wireless actuation and attachment ability for climbing tilted or slippery surfaces. To address these issues, we report alight-driven dynamic adsorption/desorption soft suction cup inspired by rock-climbing fish (Beaufortia kweichowensis). Our suction cups utilize the volumetric change caused by changes in the gas–liquid phase in the inner chamber to generate suction and thrust. The repetitive changes in the gas–liquid phase, controlled by photothermal conversion, help achieve adsorption and desorption. We demonstrated that the suction cups based on negative pressure adsorption can easily help miniaturize soft robotic devices and adapt to multiple types of substrates, making our approach applicable to tilted or slippery surfaces. By integrating the soft suction cups for surface attachment by dynamic control and a shape memory alloy as a deformable body, we developed a soft climbing robot that can perform precise, facile, and programmed controlled climbing under different conditions via remote light manipulation. Four continuous and directional climbing sequences on tilted and slippery surfaces were demonstrated. The results are expected to help advance the application of light-driven soft robots on tilted or slippery surfaces

Path Planning and Obstacle Avoidance Control for Autonomous Multi-Axis Distributed Vehicle Based on Dynamic Constraints

Obstacle avoidance problem for the autonomous vehicle has received more and more attention these years, especially for the autonomous heavy vehicle, which has the high gravity center, large carrying capacity and promising commercial prospect. However, the vehicle dynamic properties have been rarely considered for path planning, which is a crucial factor for driving safety. An integrated collision avoidance framework that consists of a new path planner and a tracking controller considering multiple dynamic constraints is proposed for an autonomous multi-axis distributed vehicle. In the upper level, a new optimal path generator based on the B-splines is designed for safety and stability purposes, and the collision avoidance path is optimized considering multiple dynamic constraints, including the tire nonlinear dynamic, lateral stability limits and the anti-slip constraints. Meanwhile, a safety assessment evaluator according to the time to collision calculation is designed for risk level recognition and path planning weight determination. In the lower level, a path tracking controller based on the nonlinear model predictive control (NMPC) is designed to improve the control accuracy, and a high-fidelity nonlinear dynamic predictive vehicle model with 16 degrees of freedom is established to depict the vehicle dynamic properties comprehensively. To solve the nonlinear optimization problem and get the optimal control steering angle output, an adaptive weight adjustment strategy and a varying predictive duration method are formulated. The optimization constraints related to steering actuator ability, plane stability limits, rollover prevention thresholds and tire adhesion requirements are constructed and converted as the bounds of the vehicle dynamic states. To verify the proposed framework, the simulation and HIL test platform are built and different driving scenarios are validated. The test results show the satisfactory performance of path planning and path tracking considering the dynamic constraints for safety and stability

Vision‐based real‐time marine and offshore structural health monitoring system using underwater robots

AbstractStructural health monitoring (SHM) plays an increasingly vital role in guaranteeing the operation success of marine and offshore (MO) structures while reducing their risks of structural failure. In this study, a real‐time MO‐SHM system based on the highly controllable underwater robots is developed, which is functionalized with three modules, that is, underwater monitoring robots, vision‐based image processing and analyzing, and time‐dependent damage assessing and early warning. The robotic module is actuated by the hybrid driving method that combines the combustion‐based actuators (ejection) and propeller thrusters (propulsion) for transient actuation ability and well reliability in complex underwater environments. The image processing and analyzing module is conducted based on the You Only Look Once (YOLO)‐Underwater model that is expanded by the transfer learning and attention mechanisms and the underwater preconditioning and warning correction added for the specific underwater concrete identification. The damage assessing and early warning module is achieved by the time‐dependent hybrid analytic hierarchy process method that is integrated with the ordered weighted averaging and entropy weight method for more objective assessment and feedback. The reported MO‐SHM system provides design guidance for the next‐generation multifunctional underwater devices that combine analyzing and early warning for underwater concrete structures.

An experimental study on the stability of hypersonic plate boundary layer regulated by a plasma actuation array

Laminar–turbulent transition control is one of the key problems in the design of hypersonic vehicles. In particular, for air-breathing hypersonic vehicles, early onset turbulence in the boundary layer of a scramjet inlet precursor is desirable. Plasma actuation has become a popular flow control method in recent years and has made progress in regulating the stability of supersonic boundary layers. However, there have been few studies on the regulation of the stability of hypersonic boundary layers. In this paper, an experimental study on the stability of the hypersonic plate boundary layer is carried out using a spanwise plasma actuation array. The characteristics and evolution of different kinds of unstable waves in the hypersonic plate boundary layer (especially the dominant first mode wave) are analyzed based on the results of linear stability theory and high-frequency pulsation sensors. The typical morphological characteristics of the boundary layer and the macro-control effect of the plasma actuation array are explored through a high-speed schlieren method. Finally, based on grayscale mode extraction and proper orthogonal decomposition, the influences of three different actuation frequencies on the instability waves and characteristic structure of the boundary layer are studied, including the dominant frequency of the first mode wave, the half-frequency of the dominant frequency of the first mode wave, and the dominant frequency of the second mode wave, the change of characteristic structures under the regulation of plasma actuation is further discussed. The corresponding regulation rules and mechanisms are summarized. The results show that the plasma actuation array can advance the starting position of laminar discontinuities and that the induced coherent structure can excite instabilities at an earlier flow-direction position. The actuation can be used to control the stability of the boundary layer by acting on the first mode wave to break the original unstable wave spectrum characteristics. This verifies the ability of extensional array plasma actuation to regulate the stability of the hypersonic plate boundary layer and suggests it has great potential in the promotion of hypersonic boundary layer transition.

Investigation of hypersonic cone boundary layer stability regulation with plasma actuation

Boundary layer transition has always been a frontier in the field of fluid mechanics, and hypersonic boundary layer stability experiments can help reveal the physical mechanisms behind such transitions. In particular, the regulation of unstable waves in boundary layers is critical for transition prediction and control. Plasma actuation is a popular flow control method that has made progress in moderating the stability of supersonic boundary layer. However, there have been few studies on regulating the stability of hypersonic boundary layers with plasma actuation. In this paper, wind tunnel experiments are carried out under Mach 6 flow to study the stability regulation of a hypersonic sharp cone boundary layer with nanosecond pulsed plasma actuation. First, the typical characteristic structure of the rope-like structure is captured by the high-speed schlieren method. Then, combining the sensor results and theoretical analysis, the rope-like structure and the dominant instability wave resolved by the schlieren power spectrum density method are determined to correspond to the second-mode wave. The characteristic unstable quasi-ordered structure of the boundary layer under actuation is then extracted, and the impact effect and modulation effect of this structure on the second-mode wave are analyzed. Finally, the mechanism by which actuation influences the boundary layer instability is studied using proper orthogonal decomposition. The results show that actuation can enhance boundary layer pulsation, and the coupling effect between the actuation and boundary layer can produce regular unstable quasi-ordered structures. The intrinsic mechanism works by impinging on and modulating the second-mode waves, and there are characteristic modes of the rope-like structure and the unstable structures distributed over the whole flow-direction range. This verifies the ability of plasma actuation to stimulate the instability of hypersonic cone boundary layers and provides technical support for the further development of transition control methods.

Narrow response temperature range with excellent reversible shape memory effect for semi-crystalline networks as soft actuators.

Complex and controlled reversible actuation inevitably relies on changing thermal fields (direct or indirect) for semi-crystalline reversible shape memory networks. Unfortunately, the non-tunability of thermal signals often brings potential limitations to actuators' applications. In practice, a wide response temperature range (T-range) formed by Thigh and Tlow in the remarkable reversible actuation is an obvious fact. Herein, we demonstrate the tunability of the transition temperatures while stably maintaining excellent actuation abilities. We further verified that the narrow T-range (24 °C) that had not been reported could present more than 17% reversible strain. Special parameter optimization provides opportunities for potential non-implantable biomedical applications. Therefore, based on target 2W-SMP, a vehicle concept with the drug release and vehicle recovery ability was proposed, proving our approach's feasibility.

Controlled Diels-Alder "Click" Strategy to Access Mechanically Aligned Main-Chain Liquid Crystal Networks.

Aligned liquid crystal polymers are materials of interest for electronic, optic, biological and soft robotic applications. The manufacturing and processing of these materials have been widely explored with mechanical alignment establishing itself as a preferred method due to its ease of use and widespread applicability. However, the fundamental chemistry behind the required two-step polymerization for mechanical alignment has limitations in both fabrication and substrate compatibility. In this work we introduce a new protection-deprotection approach utilizing a two-stage Diels-Alder cyclopentadiene-maleimide step-growth polymerization to enable mild yet efficient, fast, controlled, reproducible and user-friendly polymerizations, broadening the scope of liquid crystal systems. Thorough characterization of the films by DSC, DMA, POM and WAXD show the successful synthesis of a uniaxially aligned liquid crystal network with thermomechanical actuation abilities.

Controlled Diels–Alder “Click” Strategy to Access Mechanically Aligned Main‐Chain Liquid Crystal Networks

AbstractAligned liquid crystal polymers are materials of interest for electronic, optic, biological and soft robotic applications. The manufacturing and processing of these materials have been widely explored with mechanical alignment establishing itself as a preferred method due to its ease of use and widespread applicability. However, the fundamental chemistry behind the required two‐step polymerization for mechanical alignment has limitations in both fabrication and substrate compatibility. In this work we introduce a new protection‐deprotection approach utilizing a two‐stage Diels–Alder cyclopentadiene‐maleimide step‐growth polymerization to enable mild yet efficient, fast, controlled, reproducible and user‐friendly polymerizations, broadening the scope of liquid crystal systems. Thorough characterization of the films by DSC, DMA, POM and WAXD show the successful synthesis of a uniaxially aligned liquid crystal network with thermomechanical actuation abilities.

A stretchable and conductive design based on multi-responsive hydrogel for self-sensing actuators

Intelligent hydrogel materials have significant potential for soft robotic applications due to their sharply and reversibly responding to various external stimuli. However, obtaining a biomimetic hydrogel actuator with integrated self-sensing and self-actuation properties is still a great challenge. Herein, a multifunctional conductive hydrogel is fabricated by incorporating a conductive polymer polyaniline (PANI) into a double network poly(N-isopropylacrylamide-co-acrylamide)/poly(vinyl alcohol) (PNA/PVA) hydrogel. The as-prepared conductive PNA/PVA/PANI hydrogel could span a wide range of mechanical properties and phase transition temperatures by simply tuning polymer composition. When combined the active PNA/PVA/PANI layer with a passive polyacrylamide (PAAM) layer, a bilayer hydrogel actuator exhibits superior actuation ability with high bending speeds by the thermal stimulation. In addition, the introduction of PANI component endows the PNA/PVA/PANI hydrogel with excellent electrical conductivity up to 3.91 ± 0.15 S/m and ultrahigh-efficiency of photothermal conversion. Consequently, the PNA/PVA/PANI hydrogel not only exhibits piezoresistive strain/pressure sensing in motion recognition and physiological signal monitoring, but also displays a variety of precise and remotely driven photo-responsive locomotion such as contraction, bending, light tracking and weightlifting by locally near-infrared (NIR) illumination. Furthermore, this hydrogel can simultaneously detect these actuation states via real-time resistance change, achieving closed-loop monitoring and sensing feedback. The self-sensing actuation performance has been fully demonstrated by remotely controlling a hydrogel octopus’s grasping and object moving activities. The multi-responsiveness and real-time sensory feedback will inspire this material to be applied in novel soft biomimetic actuating materials and systems.

Redundant Electromagnetic Control of an Endoscopic Magnetic Capsule Driven by Multiple Electromagnets Configuration

In this article, we present a novel stationary electromagnetic actuation system (EMS) and a redundant magnetic field control approach that can enhance the magnetic actuation ability for a capsule endoscope. The EMS configured with multiple electromagnets has an intrinsic redundant problem when computing input current to each coil from inverse formulation. Here, we propose a redundant electromagnetic field control scheme of utilizing this redundancy to increase magnetic force and reduce the peak input current that deteriorates the performance. It is based on the optimization of magnetic field encountering input current and null-space equations of a pseudoinverse matrix. We validated the proposed methods in simulation and experiments through the prototyped EMS designed by considering actual human size and a magnetic capsule endoscope. The results show significant improvements in the magnetic field and lower input current compared to the conventional method as well as extended operating time through reduced heating effects. Especially, the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in vitro</i> in a gastric phantom and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in vivo</i> experiments in a live pig could prove the practical applicability of the developed method for a magnetic capsule endoscope toward upper stomach diagnosis in the clinical environment.

Flickering of a diffusion flame: An innovative way of stabilization by a mechanical actuator

Flickering is an oscillating instability of a diffusion flame. An experimental study has been performed on two different diffusion flame of methane and ethylene to elucidate flickering instability and controlling it by the mean of a mechanical stabilizer. Flame imaging and temporal evolution of transmitted signal methods have been employed to monitor the flame behavior and measure flickering frequency. Three different regimes of stability are identified: stable, transient, and full unstable. The measured flickering frequency of ethylene flame is 11 Hz and it is demonstrated to be independent of fuel jet velocity. The calculated vortex mean velocity is 500 mm/s and 800 mm/s without and with “pinch-off” formation respectively and the “pinch-off” velocity is around 1450 mm/s. Moreover, the ability of a mechanical actuator to stabilize the flame has been demonstrated for methane and ethylene. The experiment reveals the existence of a limit of stabilizing height at each flowrate. However, positioning stabilizer below the burner shows a limited effect. Numerical simulation shows a smoother effect of stabilizer on air streamlines around the flame limiting the action of vortex on the flame. These results prove that flickering instability could be suppressed by only controlling the air surrounded the flame.

Locomotion via Active Suction in a Sea Star-Inspired Soft Robot

Some marine animals, such as sea stars, have developed versatile adhesive appendages that can be used for a variety of behaviors including sticking to surfaces, manipulating objects, and locomoting. These appendages couple reversible adhesion capabilities with muscular structures that can do work on the world while still being soft enough to conform to various surfaces and to squeeze through tight spaces. We took inspiration from the hydraulic tube feet of sea star to create modules consisting of soft active suction discs and soft pneumatic linear actuators. Tube feet convert fluid motion into linear actuation using soft tubes that are constrained radially. In this work, we study the tradeoff between the stiffness of such radial constraints, and the ability of the linear actuators to apply axial forces. The adhesive force of the suction disc is dependent on both the pressure differential between the suction cavity and the environment and the deformation within the body of the disc while it is being loaded. We show that the tube foot modules are capable of creating locomotion over flat surfaces, up small steps, and in a confined space due to the redundancy caused by an array of actuators. We also show that active suction not only enables the use of softer tube foot actuators, but that sensing this active suction line provides feedback to increase the efficiency of locomotion over obstacles.

Effect of flow structure frequency on flow separation control using dielectric barrier discharge actuator

A better understanding of the mechanism of flow separation suppression by a dielectric barrier discharge is essential for flow control. This paper investigates the mechanism of improving the aerodynamic performance of the airfoil by dielectric barrier discharge when the Reynolds number is in the range of 6 × 104–4 × 105. The results show that the disturbance of the gas discharge to the flow field will form a new flow structure. The fluctuating frequency of the new flow structure determines the ability of the plasma actuator to suppress flow separation. This investigation improves and develops the mechanism of plasma flow control.

Computational 2D parameter study of suction and oscillatory blowing actuator with experimental validation

Fluidic oscillators and ejectors were combined to create an effective flow control device, proved effective but have not been optimized yet. In the current study, mostly steady RANS simulations were used to optimize 11 geometric parameters of a generic-simplified suction and oscillatory blowing actuator (SaOB). Selected unsteady simulations and experiments validated the numerical optimization procedure findings. In the parameter optimization process, multiple input and output parameters are chosen to identify the strongest correlations between them. Non- or weakly- correlated parameters are eliminated from further study and others are combined to obtain a reduced set of correlated parameters. It was found that the Throat ratio (ejector to oscillator) parameter predicts the Entrainment ratio, while the cross-flow pressure gradient ratio can predict the ability of the SaOB actuator to produce effective oscillation. The optimized device performs significantly better than the starting point device.While the approach is appealing, open questions remain concerning the comparison of 2D simulations and the actual 3D geometry and compressibility effects.

Screening Biophysical Sensors and Neurite Outgrowth Actuators in Human Induced-Pluripotent-Stem-Cell-Derived Neurons.

All living cells maintain a charge distribution across their cell membrane (membrane potential) by carefully controlled ion fluxes. These bioelectric signals regulate cell behavior (such as migration, proliferation, differentiation) as well as higher-level tissue and organ patterning. Thus, voltage gradients represent an important parameter for diagnostics as well as a promising target for therapeutic interventions in birth defects, injury, and cancer. However, despite much progress in cell and molecular biology, little is known about bioelectric states in human stem cells. Here, we present simple methods to simultaneously track ion dynamics, membrane voltage, cell morphology, and cell activity (pH and ROS), using fluorescent reporter dyes in living human neurons derived from induced neural stem cells (hiNSC). We developed and tested functional protocols for manipulating ion fluxes, membrane potential, and cell activity, and tracking neural responses to injury and reinnervation in vitro. Finally, using morphology sensor, we tested and quantified the ability of physiological actuators (neurotransmitters and pH) to manipulate nerve repair and reinnervation. These methods are not specific to a particular cell type and should be broadly applicable to the study of bioelectrical controls across a wide range of combinations of models and endpoints.

Modeling of Fluidic Prestressed Composite Actuators With Application to Soft Robotic Grippers

Soft and continuously controllable grippers can be assembled from fluidic prestressed composite (FPC) actuators. Due to their highly deformable features, it is difficult to model such actuators for large deflections. This article proposes a new method for modeling large deflections of FPC actuators called the chained composite model (CCM) to characterize the quasi-static response to an applied fluid pressure and load. The CCM divides an FPC actuator into discrete elements and models each element by a small rotation model. The strain energy of each element and the work done by pressure and loads are computed using third-order displacement polynomials with unknown coefficients; then, the total energy is minimized to calculate stable shapes using the Rayleigh–Ritz method. This study provides a set of systematic design rules to help the robotics community create FPC actuators by understanding how their responses vary as a function of input forces and pressures for a number of modeling and design parameters. Composite actuators are fabricated and a soft gripper is developed to demonstrate the grasping ability of the FPC actuators. Pneumatic pressure and end loads are applied to the composite actuators, and their responses are measured. The modeled responses of the actuators are shown to be in agreement with the measured responses.

Dual neural networks based active fault-tolerant control for electromechanical systems with actuator and sensor failure

The fault detection and fault-tolerant control ability of electromechanical actuator is very important especially for safety-oriented aircraft industry. In this paper, a novel active fault-tolerant control strategy based on double neural networks combined with improved fast integral terminal sliding mode control is proposed. The faults only related to the system states are considered, which is very common in electromechanical system. Considering their strong approximation ability, two neural networks with different inputs are added in a high-gain observer to estimate system model uncertainties and fault respectively. Thus, the fault detection observer can be sensitive to faults without false alarm. An integral term of position error is introduced into a fast terminal sliding surface to design an improved controller. Model uncertainties and fault are compensated for in the controller with feedforward cancellation technique based on neural networks’ estimation. The Lyapunov stability theory can guarantee the bounded stability of the proposed control strategy. Extensive comparative simulations and experimental results are obtained to verify the better performance of the proposed control strategy compared with some other traditional fault tolerant strategy.