Response Of Actuator Research Articles

Dynamic chemical bonds design strategy for fabricating fast room-temperature healable dielectric elastomer with significantly improved actuation performance

Dielectric elastomers are indispensable for soft actuators due to their fast actuation response and diverse configuration. However, the existing dielectric elastomers have poor electromechanical performance and are vulnerable to damage or failure, highlighting an urgent need for materials with remarkable dielectric, mechanical and self-healing properties. Aiming at these requirements, we herein propose an extraordinary design strategy of supramolecular elastomer by combining multitype dynamic chemical bonds via synthesizing, which is different from most previously reported dielectric elastomers. This strategy includes three typical features: (i) The S-S metathesis coupled with multi-degree hydrogen bonds provides the supramolecular poly(urethane-urea) (PUU) elastomer with fast room-temperature healability and ultrahigh efficiency. After mechanical damage, the electrical property completely recovered after ∼ 20 min restoration, and the mechanical performance is restored by 96% after healing at room temperature for 3 h, much higher than that of the elastomer without disulfide bonds (13%). (ii) Highly polar urethane and urea groups endow the supramolecular PUU elastomer with excellent dielectric properties (εr = 10.9@1 kHz). (iii) The aliphatic disulfide bonds have the capability to reduce the Young's modulus from 2.98 to 1.76 MPa by virtue of its dynamic exchange characteristic. These merits allow the resulting actuator to be more sensitive to driving field. Compared with the control sample, the area strain (at 60 MV/m) and bending angle (at 30 MV/m) for supramolecular elastomer is ∼ 4 and ∼ 2.2 times higher, respectively. As an example, a switch controlling a series circuit illustrates the potential application of such electric-field-activated actuators in high-voltage devices.

On the Effect of the Volumetric Deformation in Soft Dielectric Composites with High Phase Contrast

Towards the accurate modelling of soft dielectric composites, this investigation aims at demonstrating that the incompressibility constraint customarily adopted in the literature may lead to largely inaccurate predictions. This claim is grounded on the premise that, even though in these composites each phase may individually be assumed to be incompressible, the volumetric deformation of the softest phase can provide a significant contribution to the effective behaviour if the phase contrast is high enough. To reach our goal, we determine the actuation response of two-phase dielectric laminated composites (DLCs) where the softest phase admits volumetric deformation. Our results, discussed in the light of the limit case in which the softest phase consists of vacuum, on the one hand, challenge the hypotheses usually assumed in the modelling of soft dielectric composites and, on the other hand, are expected to provide useful information for the design of high-performance hierarchical DLCs.

A method of designing a prescribed energy landscape for morphing structures

A desired energy landscape can achieve ease of actuation and precise actuation response for a morphing structure. This paper considers morphing structures consisting of (1) pin-jointed rigid bars and hinge-joined plates and (2) torsional and translational springs. A prescribed energy landscape during motion is targeted for such a structure through optimizing the spring parameters, i.e., spring rest positions and stiffness. The method proposed in this paper first analyzes the mechanism numerically and then solves for the spring parameters to yield an energy landscape closely matching the target. This general approach is applicable to complex structures where the analytical solution of kinematics is not available. Various examples are provided to demonstrate the design process and the effectiveness of the method.

Feasibility analysis of novel Maglev EDM by comparing with conventional micro EDM

EDM is the most popular unconventional machining process. The present technology of EDM consists of a pulsed or capacitive type power supply in which the pulsed type power supply is more popular and effective. The following essential component of an EDM is its servo mechanism, which controls the gap between the electrodes and maintains the gap voltage. A low machining speed, complex power supply, and servo mechanism increase the cost of machining and the maintenance cost of an EDM machine. To resolve the above issues from the EDM, a novel servo mechanism has been developed, which is simple in design and low in cost and has the capacity to use direct current as a power source. The current work elaborates a brief description of the novel servo mechanism and its feasibility analysis. Pure DC power is employed with the conjunction of Maglev lucidity to refine the shortcomings of conventional micro EDM. The novel technology addresses the prime concerns of conventional micro EDMs and deficiencies such as the delayed response of mechanical actuators and a servo mechanism. The novel technology uses the logical arrangement of permanent magnets and electromagnets to address inadequacies such as short circuiting and arcing. The work outlook is to establish the viability of the novel Maglev EDM by a comparison with a similar range of parameters. The results on the novel technology showed an improved material removal rate (MRR), which was in the range of 76.6 μgm/min, whereas the specific energy and surface roughness were 33.4 Joule/microgram and 4.3 μm, respectively, while machining commercially pure titanium.

Design, Computational Modelling and Experimental Characterization of Bistable Hybrid Soft Actuators for a Controllable-Compliance Joint of an Exoskeleton Rehabilitation Robot

This paper presents the mechatronic design of a biorobotic joint with controllable compliance, for innovative applications of “assist-as-needed” robotic rehabilitation mediated by a wearable and soft exoskeleton. The soft actuation of robotic exoskeletons can provide some relevant advantages in terms of controllable compliance, adaptivity and intrinsic safety of the control performance of the robot during the interaction with the patient. Pneumatic Artificial Muscles (PAMs), which belong to the class of soft actuators, can be arranged in antagonistic configuration in order to exploit the variability of their mechanical compliance for the optimal adaptation of the robot performance during therapy. The coupling of an antagonistic configuration of PAMs with a regulation mechanism can achieve, under a customized control strategy, the optimal tuning of the mechanical compliance of the exoskeleton joint over full ranges of actuation pressure and joint rotation. This work presents a novel mechanism, for the optimal regulation of the compliance of the biorobotic joint, which is characterized by a soft and hybrid actuation exploiting the storage/release of the elastic energy by bistable Von Mises elastic trusses. The contribution from elastic Von Mises structure can improve both the mechanical response of the soft pneumatic bellows actuating the regulation mechanism and the intrinsic safety of the whole mechanism. A comprehensive set of design steps is presented here, including the optimization of the geometry of the pneumatic bellows, the fabrication process through 3D printing of the mechanism and some experimental tests devoted to the characterization of the hybrid soft actuation. The experimental tests replicated the main operating conditions of the regulation mechanism; the advantages arising from the bistable hybrid soft actuation were evaluated in terms of static and dynamic performance, e.g., pressure and force transition thresholds of the bistable mechanism, linearity and hysteresis of the actuator response.

Approximate field measures for ionic polymer-metal composite materials and a simplified order-of-magnitude actuator model

As the field of soft robotics grows and new applications for this technology are discovered, the use of simplified models for the soft actuators found in these devices will be critical. In this study we explore arguments based on the magnitude of field gradients that arise in the ionic polymer-metal composite (IPMC) under large applied voltages and their use for approximating measures of the fields inside the polymer. Using the order-of-magnitude based arguments provides exceptional results for quantifying the field measures of maximum ionic concentration and electric potential within the bulk of the polymer. These measures are leveraged to reconstruct the fields themselves in such a way that the internal bending moments generated inside the actuator may be approximated. With the internal moments, a simplified kinematic model may be used to formulate the steady-state actuator response of the IPMC. This actuator model shows a great deal of accuracy as compared to a full multiphysics model, and we discuss the prospects for future development of this model to account for dynamic actuation.

Buckling Electrothermal NEMS Actuators: Analytic Design for Very Slender Beams

Analytic approximations are presented for the response of buckling-mode electrothermal actuators with very slender beams with a width-to-length ratio of W/L≤0.001 of the type found in nanoelectromechanical systems (NEMS). The results are found as closed-form solutions to the Euler beam bending theory rather than by an iterative numerical solution or a time-consuming finite element analysis. Expressions for transverse deflections and stiffness are presented for actuators with the common raised cosine and chevron pre-buckled shapes. The approximations are valid when the effects of bending dominate over those of axial compression. A few higher-order approximations are also presented for less slender beams with 0.001≤W/L≤0.01.

An improved smooth shift strategy for clutch mechanism of heavy tractor semi-trailer automatic transmission

The shift quality of an automatic transmission (AT) has a significant impact on the driving comfort, fuel economy and service life of heavy tractor semi-trailer. Existing research on shift control in such vehicles is scarce and improved shift quality can contribute to development of the transportation industry. In this study, a shift strategy using a robust tracking control algorithm for AT heavy tractor semi-trailers is proposed. A high-order dynamic model with clutch actuator and planetary gear is proposed for the heavy tractor semi-trailers. Based on the clutch slip speed, a robust control strategy consisting of feedforward, feedback, and disturbance controllers is designed to provide precise control and quick response of shift actuator. Experimental data is compared with the numerical results to validate the reliability of shift control strategy. Besides, this study analyses the influence of hitch articulation angle and steering angle of semi-trailer on disturbance torque and verifies the efficacy of the proposed controller by comparing its performance to those of a traditional proportion integral differential controller and an adaptive control method. Results show that the proposed controller is superior to the traditional controller considering the tracking error, shift time, friction work, and significantly improves shift quality.

Actuation characteristics and experimental identification of IPMC actuator for underwater biomimetic robotic application

Traditionally underwater robotic devices are driven with the help of hydraulic systems or motors. However, with the current advancement in technology and inclination towards smart structures and miniature designs, various new actuators are being utilized. Ionic polymer-metal composites (IPMC) are the smart materials that come under the category of Ionic Electro-active polymers are considered as the best suitable soft actuator material for robotic devices in the field of military, aerospace and medical applications. The soft actuator’s actuation characteristics are explored in an underwater environment using data acquisition from LabView and laser vibrometer for providing the input voltage to the IPMC and to measure the tip deflection of IPMC actuator respectively. Proportional, Integral and Derivative (PID) closed-loop response using Ziegler Nichols tuning method for getting controller gains is presented through MATLAB/Simulink simulation for better actuation based on desired output response of the actuated IPMC. An evolutionary optimization technique, Particle swarm optimization (PSO) technique has been used to tune the PID controller gains to get a snappier response. The results suggested that the IPMC actuator achieved the desired actuation response of 4 mm under the applied sinusoidal voltage. Also, it is concluded that the proposed experimental model can help researchers in getting proper actuation response from different RC characteristics of IPMC under electric potential in an underwater environment that can be used for application in the underwater biomimetic robotic devices.

Optically addressable dielectric elastomer actuator arrays using embedded percolative networks of zinc oxide nanowires.

Dielectric elastomer actuators (DEAs) are electrically driven soft actuators that generate fast and reversible deformations, enabling lightweight actuation of many novel soft robots and haptic devices. However, the high-voltage operation of DEAs combined with the paucity of soft, small high-voltage microelectronics has limited the number of discrete DEAs that can be incorporated into soft robots. This has hindered the versatility as well as complexity of the tasks that they can perform which, in practice, depends on the number of independently addressable actuating elements. This paper presents a new class of optically addressable dielectric elastomer actuators that utilize the photoconductivity of semiconducting zinc oxide nanowires to create optically switchable and stretchable electrical channels. This enables non-contact, optical control of local actuation. To illustrate the versatility of the new capabilities of this integration, we describe the response of dielectric elastomer actuators with integrated photoconductive channels, formed from thin films of percolating semiconducting nanoparticles. By using a switchable array of small light emitting diodes to optically address the actuator array, its actuation can be controlled both spatially and temporally.

Numerical Investigation on the Acceleration Vibration Response of Linear Actuator

Numerical Investigation on the Acceleration Vibration Response of Linear Actuator

Improving the Response of an Electrohydrostatic Actuation (EHA) System Using a High-Pressure Accumulator

This paper proposes an (EHA) system driven in three modes to improve the low reactivity of the existing EHA system. By using a small high-pressure accumulator, servo valve, and mode switching valve, the circuits can be changed so that they are suitable for each mode according to the driving conditions. Each of the three modes consists of the EHA mode, the hybrid mode, and the charging mode, and the EHA mode operates on the same principle as the existing EHA system. The hybrid mode is activated when high-speed position control is performed, and with the help of an add-on servo valve controller, the control volume of the hydraulic cylinder can be stiffened quickly while minimizing the use of high-pressure fluids. The charge mode serves to periodically charge the accumulator under motionless conditions in applications that allow piston holding. Simulations and experiments confirm that the responsiveness of the proposed system is much improved compared to that of the existing EHA system.

Event-Triggered Adaptive Neural Tracking Control of Flexible-Joint Robot Systems With Input Saturation

This paper investigates an event-triggered adaptive neural tracking control issue for flexible-joint robot (FJR) systems subject to unknown dynamic and input saturation. To enable the backstepping design framework to be implemented, the input saturation nonlinearity is replaced by a smooth function. In the control design, the dynamic surface control (DSC) and adaptive neural techniques are used to handle the “explosion of complexity” issue and unknown dynamics, respectively. Furthermore, to reduce the calculated burden caused by the adaptive neural reconstruction technique, three virtual parameters are updated by using the single-parameter-learning approach. To decrease the frequency of actuator response to the control command for reducing the mechanical wear of actuator, an event triggering mechanism is established between the control law and actuator. Finally, an event-triggered adaptive neural tracking control solution is proposed, which is endowed the advantages as: (1) it does not need any <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">priori</i> knowledge of FJR systems; 2) it only needs to update three unknown parameters; 3) it can reduce the transmission frequency of the control commands and the response rate of the actuator. Using the Lyapunov stability theory, the proposed event-triggered control solution ensures that all signals of the closed-loop tracking control system are bounded. Finally, the simulation results verify the effectiveness and superiority of the proposed control scheme.

Characterization of 3D printed pneumatic soft actuator

Soft robotics have been investigated to replace rigid systems due to the necessity of a safe interaction between robots and humans. These types of systems are composed of soft actuators, which create motion of the structure in a linear or rotational trajectory. Soft actuators can be made using different manufacturing processes, but the most common is mold casting. However, this manufacturing process involves several steps increasing the manufacturing time and hindering design changes. This study presents a novel design of a fully 3D printed soft pneumatic actuator, using fused deposition technology. The actuator was manufactured using the most flexible material for fused deposition printing available on the market, with a shore hardness of 60 A. This paper presents a characterization of the performance of the soft actuator under different pressure conditions. Computational simulations were made to predict the response of the soft actuator, based on previous mechanical characterization of the flexible printed material. The results were compared with the experimental measurements. The theoretical model is able to predict the response of the printed actuator with an error of less than 7%. The bellow actuator was able to bend 120° at 25 psi. Additionally, the dynamic response of the soft actuator was characterized based on three different parameters: load, frequency of pressurization, and pressure level. High values of pressure produce higher deformations and greater displacements; and load reduces the damping of the dynamic response of the actuator producing more vibration and less stabilization. Finally, two different gripper designs were tested based on the opening and closing movements of single bellow actuators. Both designs were capable of holding and lifting more than twice the actuator’s weight. The functionality of both designs were simulated and tested experimentally.

High-frequency voltage-driven vibrations in dielectric elastomer membranes

This article deals with modelling and experimental characterisation of the continuum dynamic response of dielectric elastomer actuators (DEAs) subject to high-frequency voltage excitation.DEAs are capable of large deformations in response to an electrostatic stimulus, and they show large operating bandwidths of up to a few kilohertz. Although DEA systems normally make use of simple deformation patterns and a well-defined main actuation mode, they show complex structural dynamics and mode shapes if subject to high frequency voltage inputs. Taking advantage of these complex structural dynamics potentially allows developing multi-function actuators, audio devices and vibration isolators capable to perform different tasks using different vibration regimes.We first present a multi-domain model for the structural dynamics of DEAs, accounting for the contribution of the air pressure loads generated the DEA membrane vibrations, which play a relevant role in the DEA dynamics.We then present an extensive experimental characterisation of DEA samples’ structural dynamics based on laser Doppler vibrometer measurements. In particular, we measure the complex structural mode shapes and the velocity spectra generated through a broadband excitation in correspondence of a wide set of different design and control parameters (namely, the DEA geometric layout, the mechanical-preload and the applied voltage bias).Based on the experimental results, we validate the proposed continuum model, and we demonstrate that the forced response of the DEA can be efficiently described using a lumped-parameter computationally efficient reduced reformulation.

The Soft and High Actuation Response of Graphene Oxide/Gelatin Soft Gel.

The high actuation response of soft gel from a graphene oxide/gelatin composite was prepared as an alternative material in soft robotics applications. Graphene oxide (GO) was selected as the electroresponsive (ER) particle. GO was synthesized by modifying Hummer’s method at various ratios of graphite (GP) to potassium permanganate (KMnO4). To study the effect of ER particles on electromechanical properties, GO was blended with gelatin hydrogel (GEL) at various concentrations. The electrical properties of the ER particles (GO and GP) and matrix (GEL) were measured. The capacitance (C), resistance (R), and dielectric constant of the GO/GEL composite were lower than those of the GO particles but higher than those of the GEL and GP/GEL composite at the given number of particles. The effects of external electric field strength and the distance between electrodes on the degree of bending and the dielectrophoresis force (Fd) were investigated. When the external electric field was applied, the composite bent toward electrode, because the electric field polarized the functional group of polymer molecules. Under applied 400 V/mm, the GO/GEL composite (5% w/w) showed the highest deflection angle (θ = 82.88°) and dielectrophoresis force (7.36 N). From the results, we conclude that the GO/GEL composite can be an alternative candidate material for electromechanical actuator applications.

Finite Element Model for Investigating the Thermo-Electro-Mechanical Response of Inhomogeneously Deforming Dielectric Elastomer Actuators

Among the available soft active materials, Dielectric elastomers (DEs) possess the capability of achieving the large actuation strain under the application of high electric field. The material behavior of such elastomers is affected significantly by the change in temperature. This paper reports a 3-D finite element framework based on the coupled nonlinear theory of thermo-electro-elasticity for investigating the thermal effects on the electromechanical performance of inhomogeneously deforming dielectric elastomer actuators (DEAs). The material behavior of the actuator is modeled using the neo-Hookean model of hyperelasticity with temperature dependent shear modulus. An in-house computational code is developed to implement the coupled finite element framework. Firstly, the accuracy of the developed FE code is verified by simulating the temperature effects on the actuation response and pull-in instability of the benchmark homogeneously deforming planar DE actuator. Further, the influence of temperature on the electromechanical responses of complex bi-layered bending actuator and buckling pump actuator involving inhomogeneous deformation is investigated. The numerical framework and the associated inferences can find their potential use in addressing the effect of temperature in the design of electro-active polymer based actuators.

The importance of potential range choice on the electromechanical response of cellulose - carbon nanotube fibers

Recently, an important focus of material research has been aimed at more sustainable smart materials with biodegradable, biocompatible properties such as those based on cellulose (Cell), made stimuli-responsive with the addition of multiwall carbon nanotubes (CNT). Formulated as fibers, such materials have potential applications in smart clothing and wearable’s in actuation or sensing function. In order to ensure maximum performance, an optimal driving voltage and regime must be chosen. In addition to the quantitative effects, the actuation response also qualitatively and mechanistically changes, depending on the voltage range. The linear actuation measurements combined with cyclic voltammetry and square wave potential steps were performed in aqueous lithium bis(trifluoromethane)sulfonimide solution. The Cell-CNT fiber actuation response properties were investigated at different potential ranges: 0.8–0.0 V, 0.8 V to − 0.3 V, 0.8 V to − 0.55 V and 0.65 V to − 0.6 V, observing a change in actuation direction between the ranges. Not just the potential range but also the driving frequency had an impact on the response, therefore, the selection of driving parameters is shown to be critical for controllable performance.

Photostrictive effect in 1-3 composites of photovoltaic and piezoelectric phases: A numerical study

Coalesce of photovoltaic effect with converse piezoelectric effect will turn into a photostrictive phenomenon. The current study conceptualizes a 1-3 photostrictive composite consists of a photovoltaic polymer as matrix and fibers of piezoelectric material. The proposed artificial photostrictive composite is capable of replacing lead-based naturally occurring photostrictive material, not only opening a potential for new applications but also caters to tailor the desired properties. Present study employs poly{4,8-bis[5-(2-ethyl-hexyl)thiophen-2-yl]benzo[1,2-b:4,5-b’]dithiophene-2,6-diyl-alt-3-fluoro-2-[(2-ethylhexyl) carbonyl] thieno[3,4-b] thiophene-4,6-diyl} (PTB7-Th) as organic photovoltaic polymer and Pb(Mg1/3Nb2/3)O3-0.35PbTiO3 (PMN-35PT) as the fibers. A representative volume element technique (RVE) is employed to embrace the local variation of multi-physics properties. The actuation response of cantilever and simply supported beam bonded to photostrictive composite patch is accurately predicted by finite element method, while discretizing the structure with degenerated shell element. Photostrictive composite with 60% volume fraction of fibers, arranged in square pattern have deflected the cantilever tip to 1.95 mm. Therefore, we provide 1-3 photostrictive composite as a solution for future wireless and lightweight vibration control applications.

Track-following system optimization for future magnetic tape data storage

Recently, the increase of track density has been shown to be one of the most effective methods to increase the areal bit density and thus the cartridge capacity of future magnetic tape data storage systems. Increasing the track density poses stringent positioning requirements to the tape track-following control system. In this work, we investigate four novel timing-based servo patterns, and the impact of their geometrical properties, i.e. azimuthal angle and subframe length, on the position estimation resolution, the system delay and track-following performance. First, the resolution of the patterns versus reader width is assessed by analyzing the noise floor in the power spectrum of the lateral position estimation. This methodology is used to determine the optimal reader width for each pattern. Second, the system delay for each of the new patterns is identified by measuring the frequency response of the track-following actuator. An analytical model of the delay is derived and verified with experimental data. Finally, the impact of resolution and delay on the track-following performance is investigated. The best track-following performance, characterized by a standard deviation of the position-error signal of 4.2nm, was achieved using a pattern with a 36°azimuthal angle. The performance could be further improved down to 4.0nm by time averaging the position estimates.