Showing papers on "Actuator published in 2018"

Molecular-channel driven actuator with considerations for multiple configurations and color switching.

Abstract: The ability to achieve simultaneous intrinsic deformation with fast response in commercially available materials that can safely contact skin continues to be an unresolved challenge for artificial actuating materials. Rather than using a microporous structure, here we show an ambient-driven actuator that takes advantage of inherent nanoscale molecular channels within a commercial perfluorosulfonic acid ionomer (PFSA) film, fabricated by simple solution processing to realize a rapid response, self-adaptive, and exceptionally stable actuation. Selective patterning of PFSA films on an inert soft substrate (polyethylene terephthalate film) facilitates the formation of a range of different geometries, including a 2D (two-dimensional) roll or 3D (three-dimensional) helical structure in response to vapor stimuli. Chemical modification of the surface allowed the development of a kirigami-inspired single-layer actuator for personal humidity and heat management through macroscale geometric design features, to afford a bilayer stimuli-responsive actuator with multicolor switching capability. Intrinsic deformation with fast response in commercially available materials that can safely contact skin continues to be a challenge for artificial actuating materials. Here the authors incorporate nanoscale molecular channels within perfluorosulfonic acid ionomer for self-adaptive and ambient-driven actuation.

Kirigami skins make a simple soft actuator crawl

Abstract: Bioinspired soft machines made of highly deformable materials are enabling a variety of innovative applications, yet their locomotion typically requires several actuators that are independently activated. We harnessed kirigami principles to significantly enhance the crawling capability of a soft actuator. We designed highly stretchable kirigami surfaces in which mechanical instabilities induce a transformation from flat sheets to 3D-textured surfaces akin to the scaled skin of snakes. First, we showed that this transformation was accompanied by a dramatic change in the frictional properties of the surfaces. Then, we demonstrated that, when wrapped around an extending soft actuator, the buckling-induced directional frictional properties of these surfaces enabled the system to efficiently crawl.

Hygrobot: A self-locomotive ratcheted actuator powered by environmental humidity

Abstract: Microrobots that are light and agile yet require no artificial power input can be widely used in medical, military, and industrial applications. As an actuation system to drive such robots, here we report a biologically inspired bilayer structure that harnesses the environmental humidity energy, with ratchets to rectify the motion. We named this actuator-ratchet system the hygrobot. The actuator uses a hygroscopically responsive film consisting of aligned nanofibers produced by directional electrospinning, which quickly swells and shrinks in lengthwise direction in response to the change of humidity. The ratchets based on asymmetric friction coefficients rectify oscillatory bending motion in a directional locomotion. We mathematically analyzed the mechanical response of the hygrobot, which allowed not only prediction of its performance but also the optimal design to maximize the locomotion speed given geometric and environmental constraints. The hygrobot sterilized a trail across an agar plate without any artificial energy supply.

Carbon-Based Photothermal Actuators

Abstract: Actuators that can convert environmental stimuli into mechanical work are widely used in intelligent systems, robots, and micromechanics. To produce robust and sensitive actuators of different scales, efforts are devoted to developing effective actuating schemes and functional materials for actuator design. Carbon-based nanomaterials have emerged as preferred candidates for different actuating systems because of their low cost, ease of processing, mechanical strength, and excellent physical/chemical properties. Especially, due to their excellent photothermal activity, which includes both optical absorption and thermal conductivities, carbon-based materials have shown great potential for use in photothermal actuators. Herein, the recent advances in photothermal actuators based on various carbon allotropes, including graphite, carbon nanotubes, amorphous carbon, graphene and its derivatives, are reviewed. Different photothermal actuating schemes, including photothermal effect–induced expansion, desorption, phase change, surface tension gradient creation, and actuation under magnetic levitation, are summarized, and the light-to-heat and heat-towork conversion mechanisms are discussed. Carbon-based photothermal actuators that feature high light-to-work conversion efficiency, mechanical robustness, and noncontact manipulation hold great promise for future autonomous systems.

The Design of Fixed-Time Observer and Finite-Time Fault-Tolerant Control for Hypersonic Gliding Vehicles

Abstract: This paper proposes a fault-tolerant control (FTC) scheme for a hypersonic gliding vehicle to counteract actuator faults and model uncertainties. Starting from the kinematic and aerodynamic models of the hypersonic vehicle, the control-oriented model subject to actuator faults is built. The observers are designed to estimate the information of actuator faults and model uncertainties, and to guarantee the estimation errors for converging to zero in fixed settling time. Subsequently, the finite-time multivariable terminal sliding mode control and composite-loop design are pursued to enable integration into the FTC, which can ensure the safety of the postfault vehicle in a timely manner. Simulation studies of a six degree-of-freedom nonlinear model of the hypersonic gliding vehicle are carried out to manifest the effectiveness of the investigated FTC system.

Translucent soft robots driven by frameless fluid electrode dielectric elastomer actuators.

Abstract: Dielectric elastomer actuators (DEAs) are a promising enabling technology for a wide range of emerging applications, including robotics, artificial muscles, and microfluidics. This is due to their large actuation strains, rapid response rate, low cost and low noise, high energy density, and high efficiency when compared with alternative actuators. These properties make DEAs ideal for the actuation of soft submersible devices, although their use has been limited because of three main challenges: (i) developing suitable, compliant electrode materials; (ii) the need to effectively insulate the actuator electrodes from the surrounding fluid; and (iii) the rigid frames typically required to prestrain the dielectric layers. We explored the use of a frameless, submersible DEA design that uses an internal chamber filled with liquid as one of the electrodes and the surrounding environmental liquid as the second electrode, thus simplifying the implementation of soft, actuated submersible devices. We demonstrated the feasibility of this approach with a prototype swimming robot composed of transparent bimorph actuator segments and inspired by transparent eel larvae, leptocephali. This design achieved undulatory swimming with a maximum forward swimming speed of 1.9 millimeters per second and a Froude efficiency of 52%. We also demonstrated the capability for camouflage and display through the body of the robot, which has an average transmittance of 94% across the visible spectrum, similar to a leptocephalus. These results suggest a potential for DEAs with fluid electrodes to serve as artificial muscles for quiet, translucent, swimming soft robots for applications including surveillance and the unobtrusive study of marine life.

Error-Constrained LOS Path Following of a Surface Vessel With Actuator Saturation and Faults

Abstract: This paper presents an error-constrained line-of-sight (ECLOS) path-following control method for a surface vessel subject to uncertainties, disturbances, and actuator saturation and faults. Based on a cascaded three degrees-of-freedom model of surface vessel, the backstepping technique is adopted as the main control framework. Error constraint of the vessel position is handled by integrating a novel tan-type barrier Lyapunov function. The proposed ECLOS method is in accordance with the classical line-of-sight method where no constraint is imposed. A nonlinear disturbance observer is developed to estimate the lumped disturbance that comprises the effects of parametric uncertainties, external environment disturbances, and actuator saturation and faults. It is proved that under the proposed control, the constrained requirements on the vessel position error are never violated and all closed-loop signals are uniformly ultimately bounded, regardless of fully actuated or under-actuated control configuration. Simulation results and comparisons illustrate the effectiveness and advantages of the proposed ECLOS path-following method.

Reconfigurable photoactuator through synergistic use of photochemical and photothermal effects.

Abstract: A reconfigurable actuator is a stimuli-responsive structure that can be programmed to adapt different shapes under identical stimulus. Reconfigurable actuators that function without control circuitry and are fueled remotely are in great demand to devise adaptive soft robotic devices. Yet, obtaining fast and reliable reconfiguration remains a grand challenge. Here we report a facile fabrication pathway towards reconfigurability, through synergistic use of photochemical and photothermal responses in light-active liquid crystal polymer networks. We utilize azobenzene photoisomerization to locally control the cis-isomer content and to program the actuator response, while subsequent photothermal stimulus actuates the structure, leading to shape morphing. We demonstrate six different shapes reconfigured from one single actuator under identical illumination conditions, and a light-fueled smart gripper that can be commanded to either grip and release or grip and hold an object after ceasing the illumination. We anticipate this work to enable all-optical control over actuator performance, paving way towards reprogrammable soft micro-robotics.

Adaptive Fault-Tolerant Consensus for a Class of Uncertain Nonlinear Second-Order Multi-Agent Systems With Circuit Implementation

Abstract: In this paper, a robust fault-tolerant consensus control strategy and its circuit implementation method are proposed for a class of nonlinear second-order leader-following multi-agent systems against multiple actuator faults and time-varying state/input-dependent system uncertainties. The faults of partial loss of actuator effectiveness and bias-actuators are considered without knowing eventual faulty information. The uncertainties are supposed to be structured and to satisfy integral quadratic constraints. The nonlinear dynamics of underlying systems are described by linear state-dependent functions based on the differential mean value theorem. By designing adaptive schemes and state-feedback control gains, a novel distributed control strategy is constructed to ensure the asymptotic consensus of agents in the presence of actuator faults, uncertainties, and nonlinear dynamics. The control strategy is further physically implemented based on the circuit theory. The efficiency of the developed control circuits is verified by a multiple coupled nonlinear forced pendulum system based on a circuit simulation software.

Observer-Based Composite Adaptive Fuzzy Control for Nonstrict-Feedback Systems With Actuator Failures

Abstract: This paper studies the observer-based adaptive fuzzy tracking control problem for a general class of multi-input-single-output nonstrict-feedback systems subject to unmeasured states and actuator failures. For actuator failures, both cases of lock-in-place and loss of effectiveness are synchronously considered. To handle the unknown nonlinear functions, fuzzy logic systems are employed. By constructing a fuzzy observer and a serial-parallel estimation model, the unmeasured states are estimated and the accuracy of approximating the unknown functions is improved. Moreover, taking into account the prediction error between the fuzzy observer and the serial-parallel estimation model, a novel composite fuzzy output-feedback control scheme is developed. Unlike some existing control schemes for systems with actuator failures, the developed control scheme allows one to avoid the problem of “explosion of complexity” and improve the approximation performance. It is proved that all signals in the system are bounded and the tracking error converges to a small neighborhood of the origin by choosing appropriate parameters. Finally, the effectiveness of the proposed method is confirmed via simulation examples with actuator failures.

Graphene-based bimorphs for micron-sized, autonomous origami machines

Abstract: Origami-inspired fabrication presents an attractive platform for miniaturizing machines: thinner layers of folding material lead to smaller devices, provided that key functional aspects, such as conductivity, stiffness, and flexibility, are persevered. Here, we show origami fabrication at its ultimate limit by using 2D atomic membranes as a folding material. As a prototype, we bond graphene sheets to nanometer-thick layers of glass to make ultrathin bimorph actuators that bend to micrometer radii of curvature in response to small strain differentials. These strains are two orders of magnitude lower than the fracture threshold for the device, thus maintaining conductivity across the structure. By patterning 2- 𝝁 𝝁m-thick rigid panels on top of bimorphs, we localize bending to the unpatterned regions to produce folds. Although the graphene bimorphs are only nanometers thick, they can lift these panels, the weight equivalent of a 500-nm-thick silicon chip. Using panels and bimorphs, we can scale down existing origami patterns to produce a wide range of machines. These machines change shape in fractions of a second when crossing a tunable pH threshold, showing that they sense their environments, respond, and perform useful functions on time and length scales comparable with microscale biological organisms. With the incorporation of electronic, photonic, and chemical payloads, these basic elements will become a powerful platform for robotics at the micrometer scale.

Multistimulus Responsive Actuator with GO and Carbon Nanotube/PDMS Bilayer Structure for Flexible and Smart Devices.

Abstract: Smart devices with abilities of perceiving, processing, and responding are attracting more and more attentions due to the emerging development of artificial intelligent systems, especially in biomimetic and intelligent robotics fields Designing a smart actuator with high flexibility and multistimulation responsive behaviors to simulate the movement of creatures, such as weight lifting, heavy objects carrying via simple materials, and structural design is highly demanded for the development of intelligent systems Herein, a soft actuator that can produce reversible deformations under the control of light, thermal, and humidity is fabricated by combining high photothermal properties of CNT/PDMS layer with the natural hydrophilic GO layer Due to the asymmetric double-layer structure, the novel bilayer membrane-based actuator showed different bending directions under photothermal and humidity stimulations, resulting in bidirectional controllable bending behaviors In addition, the actuation behaviors can be well controlled by directionally aligning the graphene oxide onto carbon nanotube/PDMS layer The actuator can be fabricated into a series of complex biomimetic devices, such as, simulated biomimetic fingers, smart "tweezers", humidity control switches, which has great potential applications in flexible robots, artificial muscles, and optical control medical devices

A review of electromechanical actuators for More/All Electric aircraft systems:

Abstract: Conventional hydraulic actuators in aircraft systems are high maintenance and more vulnerable to high temperatures and pressures. This usually leads to high operating costs and low efficiency. With the rapid development of More/All Electric technology, power-by-wire actuators are being broadly employed to improve the maintainability, reliability, and manoeuvrability of future aircraft. This paper reviews the published application and development of the airborne linear electromechanical actuator. First, the general configuration, merits, and limitations of the gear-drive electromechanical actuator and the direct-drive electromechanical actuator are analysed. Second, the development state of the electromechanical actuator testing systems is elaborated in three aspects, namely the performance testing based on room temperature, testing in a thermal vacuum environment, and iron bird. Common problems and tendencies of the testing systems are summarized. Key technologies and research challenges are revealed in t...

Reconfigurable Tolerant Control of Uncertain Mechanical Systems With Actuator Faults: A Sliding Mode Observer-Based Approach

Abstract: This paper studies a key issue of developing reconfigurable fault-tolerant control to retain a nominal feedback controller and simultaneously handles actuator faults and system uncertainty, while the closed-loop system is stabilized with all control objectives achieved. A theoretical architecture of a reconfigurable control design is presented for a class of uncertain mechanical systems by using an observer technique. As a stepping stone, a nonlinear observer-based estimation mechanism is designed to reconstruct uncertain dynamics and actuator faults with the estimation error converging to zero within finite time. A reconfigurable control effort is then synthesized from the reconstructed knowledge. This control power operates as a compensation control part, and it is added to the nominal control part to accommodate system uncertainties and actuator faults. It is proved that the overall system resulted from the developed control framework has the same control performance of the nominal closed-loop system, including certain system dynamics and the nominal control effort. The effectiveness of the scheme is validated on a serial robotic manipulator.

A Piezoelectric-Driven Linear Actuator by Means of Coupling Motion

Abstract: A piezoelectric-driven actuator based on coupling motion has been proposed and tested to achieve a large linear working stroke with high resolution. “Z-shaped” flexure hinges are exploited for the symmetric flexure hinge mechanism to reduce the structural stress. Coupling motion is obtained by placing this symmetric flexure hinge mechanism with an angle of $\theta =20^\circ $ to the slider. Experimental results indicate that linear motion with a large working stroke is effectively obtained by this coupling motion; the maximum motion speed is $V_{s}=$ 6057 μm/s and the maximum output force is $F_{g}=$ 350 g. Additionally, the influences of input frequency $f$ and input voltage $U_{e}$ are investigated, and the system kinetic model is established to better analyze the performance of this designed piezoelectric-driven linear actuator.

Design and Experiments of a Single-Foot Linear Piezoelectric Actuator Operated in a Stepping Mode

Abstract: A single-foot linear piezoelectric actuator is proposed in this paper, and a new exciting method for the stepping motion is discussed The proposed actuator works in the hybrid modes of the second horizontal bending vibration and the second vertical bending vibration Two intermittent sinusoidal signals with a phase difference of 90° are applied on the horizontal and vertical PZT elements, respectively, to obtain a discontinuous elliptical motion at the driving foot, which can move the runner linearly step by step The structure of a single-foot linear piezoelectric actuator is designed and the mechanism for the linear driving is clarified Then, modal and transient analyses are carried out by using ANSYS software to get the resonance frequencies of the bending modes and the movement trajectory of the driving foot Finally, a prototype of the piezoelectric actuator is fabricated, and experiments are carried out The experiment results show that the displacement resolution, the maximum velocity, and the maximum thrust of the proposed piezoelectric actuator are about 021 μm, 8275 mm/s, and 27 N, respectively

An Adaptive Fault-Tolerant Sliding Mode Control Allocation Scheme for Multirotor Helicopter Subject to Simultaneous Actuator Faults

Abstract: This paper proposes a novel adaptive sliding-mode-based control allocation scheme for accommodating simultaneous actuator faults. The proposed control scheme includes two separate control modules with virtual control part and control allocation part, respectively. As a low-level control module, the control allocation/reallocation scheme is used to distribute/redistribute virtual control signals among the available actuators under fault-free or faulty conditions, respectively. In the case of simultaneous actuator faults, the control allocation and reallocation module may fail to meet the required virtual control signal, which will degrade the overall system stability. The proposed online adaptive scheme can seamlessly adjust the control gains for the high-level sliding mode control module and reconfigure the distribution of control signals to eliminate the effect of the virtual control error and maintain the stability of the closed-loop system. In addition, with the help of the boundary layer for constructing the adaptation law, the overestimation of control gains is avoided, and the adaptation ceases once the sliding variable is within the boundary layer. A significant feature of this study is that the stability of the closed-loop system is guaranteed theoretically in the presence of simultaneous actuator faults. The effectiveness of the proposed control scheme is demonstrated by experimental results based on a modified unmanned multirotor helicopter under both single and simultaneous actuator faults conditions with comparison to a conventional sliding mode controller and a linear quadratic regulator scheme.

Approximation-Free Control for Vehicle Active Suspensions With Hydraulic Actuator

Abstract: This paper presents a novel control strategy for nonlinear uncertain vehicle active suspension systems without using any function approximators [eg, neural networks (NNs) or fuzzy logic systems (FLSs)] Unlike previous results that neglect the effect of actuator dynamics, this paper incorporates the dynamics of a hydraulic actuator that is used to create the required active suspension forces into the controller design To address the nonlinearities of this hydraulic system, an approximation-free control method is introduced In this method, the widely used NNs and FLSs are not needed This leads to reduced computational burden and complexity, and thus, it is more suited for practical applications Moreover, by introducing a prescribed performance function and the associated error transform, the proposed controller can guarantee both the transient and steady-state suspension responses The stability of the closed-loop system and the suspension performance requirements are rigorously proved Finally, comparative simulations are conducted to validate the improved performance and robustness of the proposed method

Programmable design of soft pneu-net actuators with oblique chambers can generate coupled bending and twisting motions

Abstract: Soft pneumatic network (pneu-net) actuators are widely employed for achieving sophisticated motions. However, to produce bending and twisting simultaneously in a single pneu-net actuator is challenging. In this paper we present a programmable design to enable pneu-net actuators to achieve such complex motions. This achievement is mainly owing to tuning a structure parameter, the chamber angle. Through finite element analysis and experimental verification, variation trends of bending and twisting motions with respect to the chamber angle are investigated. Additionally, deformation characteristics of actuators are demonstrated by depicting configurations of actuators and some grasping tests. By adjusting the chamber angle, the motion of pneu-net actuators is explored into 3-D space and becomes more sophisticated and dexterous. This programmable design method guides the design of pneu-net actuators, making them promising candidates for more complicated and advanced applications.

Nonlinear Adaptive Fault-Tolerant Quadrotor Altitude and Attitude Tracking With Multiple Actuator Faults

Abstract: This brief presents the design, analysis, and implementation of a nonlinear robust adaptive fault-tolerant altitude and attitude tracking method for accommodating actuator faults in quadrotor unmanned aerial vehicles without the need of a fault diagnosis mechanism. Actuator faults are modeled as a constant loss of effectiveness in the thrust generated by the rotors. The fault-tolerant control (FTC) algorithm guarantees asymptotic convergence of the altitude and attitude tracking error even in the presence of possible multiple actuator faults and modeling uncertainties. The FTC method is implemented using a real-time indoor quadrotor test environment. Experimental results are shown to illustrate the effectiveness of the algorithm.