Actuation Efficiency Research Articles

Recent progress in the application development of Fe50Ni50 type alloys

Present and future applications for Fe50Ni50 type alloys are dependent on an ever-improving mastery of the shape of the hysteresis cycle and/or the best use of these quantities when approaching the Curie point Tc. A metallurgical solution exists to trigger anomalous grain growth at a thickness of 0.8 mm, allowing for the achievement of a coercive field less than 1.5–2 A/m which can further improve torque sensor accuracy. The lowering of Jr to reinforce the safety and efficiency of certain electromechanical actuators is obtained by adding elements, interpreted as magnetoelastic effect related to lattice deformations. The joint selection of Tc, the magnetic properties and the thermal and electromagnetic environmental conditions of the material will soon make it possible to achieve effective temperature regulations through the very nonlinear signature of the inductance as a function of temperature T at the approach of Tc.

New Robust Backstepping Attitude Control Approach Applied to Quanser 3 DOF Hover Quadrotor in the Case of Actuators Faults

In this paper, a novel robust backstepping-based fault-tolerant control is designed, implemented and validated experimentally on a quadrotor unmanned aerial vehicle testbed under actuator fault conditions for tracking control. Backstepping is known as a robust method to maintain system performance and keep it insensitive to disturbances. The proposed nonlinear controller is mainly based on the advanced robust backstepping method to solve the system uncertainties caused by disturbances and actuator faults, which appear in the motor part of the system and are compensated without diagnostics or fault identification. The various parameters of the proposed approach are optimized using the particle swarm optimization (PSO) method. Owing to the minimized control effort to accommodate uncertainties compared to the conventional backstepping, the proposed approach can still maintain the system performance when severer faults occur. The proposed approach is validated, first, in a simulation using the nonlinear model of the quadrotor, then experimentally, using the Quanser 3DOF Hover quadrotor. Both theoretical and experimental analyses have demonstrated that the effectiveness of the proposed improved backstepping fault-tolerant control strategies faces significant loss of actuator efficiency.

Increasing the Efficiency of Thermoresponsive Actuation at the Microscale by Direct Laser Writing of pNIPAM

AbstractThermoresponsive hydrogels such as poly(N‐isopropylacrylamide) (pNIPAM) are highly interesting materials for generating soft actuator systems. Whereas the material has so far mostly been used in macroscopic systems, here it is demonstrated that pNIPAM is an excellent material for generating actuator systems at the micrometer scale. Two‐photon direct laser writing is used to precisely structure thermoresponsive pNIPAM hydrogels at the micrometer scale based on a photosensitive resist. This study systematically shows that the surface‐to‐volume ratio of the microactuators is decisive to their actuation efficiency. The phase transition of the pNIPAM is also demonstrated by nanoindentation experiments. It is observed that the mechanical properties of the material can easily be adjusted by the writing process. Finally, it is found that not only the total size and surface structure of the microactuator play an important role, but also the crosslinking of the polymer itself. The results demonstrate for the first time a systematic study of pNIPAM‐based microactuators, which can easily be extended to systems of microactuators that act cooperatively, e.g., in microvalves.

Numerical investigation of flow over a two-dimensional square cylinder with a synthetic jet generated by a bi-frequency signal

The flow around a square cylinder with a synthetic jet positioned at the rear surface is numerically investigated with the unsteady Reynolds-averaged Navier-Stokes (URANS) method. Instead of the typical sinusoidal wave, a bi-frequency signal is adopted to generate the synthetic jet. The bi-frequency signal consists of a basic sinusoidal wave and a high-frequency wave. Cases with various amplitudes of the high-frequency component are simulated. It is found that synthetic jets actuated by bi-frequency signals can realize better drag reduction with lower energy consumption when appropriate parameter sets are applied. A new quantity, i.e., the actuation efficiency Ae, is used to evaluate the controlling efficiency. The actuation efficiency Ae reaches its maximum of 0.266 8 when the amplitude of the superposed high-frequency signal is 7.5% of the basic signal. The vortex structures and frequency characteristics are subsequently analyzed to investigate the mechanism of the optimization of the bi-frequency signal. When the synthetic jet is actuated by a single-frequency signal with a characteristic velocity of 0.112 m/s, the wake is asymmetrical. The alternative deflection of vortex pairs and the peak at half of the excitation frequency in the power spectral density (PSD) function are detected. In the bi-frequency cases with the same characteristic velocity, the wake gradually turns to be symmetrical with the increase in the amplitude of the high-frequency component. Meanwhile, the deflection of the vortex pairs and the peak at half of the excitation frequency gradually disappear as well.

Real-time hybrid gait phase recognition algorithm under continuous multimodal locomotion for lower limb exoskeleton

Nowadays, exoskeletons' ability to operate in complex environments is increasingly important. It is challenging to obtain an accurate gait phase under continuous multimodal locomotion. A hybrid gait phase recognition algorithm is proposed combining the adaptive-oscillator-based algorithm and the model-based algorithm. The modification law is adopted to make two algorithms amend each other reciprocally. The design of the modification law combines the advantages of oscillator-based algorithms and model-based algorithms. The gait phase estimation results are more accurate via the hybrid gait phase prediction algorithm (GPRA). Therefore, appropriate assistance actuation and higher efficiency are obtained under the complicated multimodal locomotion. An experiment was designed to verify the performance of the hybrid GPRA. As a result, the hybrid GPRA can still produce a high-precision gait phase with low latency even when the locomotion mode switches. The hybrid GPRA can provide accurate gait phase and assistance timing under continuous multimodal locomotion.

Passive air leakage detection mechanism for enhanced vacuum suction actuator efficiency

Passive air leakage detection mechanism for enhanced vacuum suction actuator efficiency

Efficient Design Guidelines for Innovative Aerial Robot Design

Abstract The field of aerial robotics has advanced rapidly, but the design knowledge has not yet been codified into reusable design guidelines. Design guidelines have been developed for many mechanical design areas to advance the field itself and help novice designers benefit from past expert knowledge more easily. We used an inductive approach and collected 90 aerial robot examples by reviewing recent work in aerial robotics and studying the key motivations, features, functionalities, and potential design contradictions. Then, design guidelines are derived by identifying patterns and grouping them by the problem they solve and the innovation made to solve it iteratively. From this, we find 35 unique design examples that can be grouped into either 14 design guidelines for more sensing, battery, mission, or actuation efficiency; or to improve the desired functionality in an aerial robot such as reducing complexity or improving how the robot can interact with objects or its environment. The derived guidelines are validated for thematic saturation using convergence analysis and its utility through a qualitative design study involving novices and experienced designers working on two design problems. The design guidelines presented in this research can support the design of future innovative aerial robots.

Energy conversion analysis of ion wind in surface dielectric barrier discharge at low pressure

Ionic wind actuators are widely used in temperature control, food drying, aircraft propulsion, combustion, air purification, and many other fields. The energy conversion efficiency of ion-wind actuator has been low for a long time. In this paper, a lumped parameter circuit model is established for the surface dielectric barrier discharge structure, and the energy conversion path in the discharge process is proposed for the first time. According to the circuit topology, part of the energy loss is calculated. Based on the mathematical calculations of the circuit model, we discovered the possibility of “negative capacitance effect” in the plasma area, and the experimental verified the correctness of the theoretical deduction and prediction. Meanwhile, the results show that the equivalent capacitance of the solid dielectric is equal to the bottom slope of Lissajous graph, and the negative capacitance effect can effectively reduce the proportion of solid dielectric loss and relaxed polarization loss. The negative capacitance effect improves the energy conversion efficiency of the ionic wind exciter, and the maximum increase ratio is about 47.8%. With the increase of voltage, the deviation between the calculated value of theoretical model and the measured value increases gradually, and finally stabilizes at about 41%.

A novel three-dimensional center energy deposition model for the hybrid synthetic jet actuator

The low energy conversion efficiency of the plasma synthetic jet actuator (PSJA) and the misfiring problem caused by the low gas backfill rate have hindered the application of the PSJA in supersonic aircraft for fast response aerodynamic control. Although the hybrid synthetic jet actuator (HSJA) based on the PSJA has the potential to solve these problems, the heat and mass transfer mechanism of hybrid synthetic jets is still unclear. According to the capacitive discharge process, a novel three-dimensional center energy deposition model was proposed in this paper. The accuracy of the three-dimensional center energy deposition model was verified by comparing it with the experimental results. Considering the damped oscillation of the discharge intensity, the effect of nonconstant center energy deposition on the heat and mass transfer inside the cavity was further discussed. The simulation results show that the electrodes have an impact on the creation and evolution of the vortices inside the cavity. And the three-dimensional nonconstant center energy deposition model reveals the real heat and mass transfer mechanism of the HSJA, which provides the theoretical foundation for improving energy conversion efficiency and gas backfill rate of the HSJA.

Efficiency assessment of a single surface dielectric barrier discharge plasma actuator with an optimized Suzen–Huang model

Spatial and time-resolved characteristics of a single surface dielectric barrier discharge (sDBD) actuator are experimentally and numerically investigated. The paper also focuses on the efficiency of sDBD actuators used as flow-control devices. The motivation is the need for developing a cost-effective way to optimize the balance between control performance and actuator power consumption. The study considers the steady state as often employed in experiments as well as the transient regime. Experimental methods to obtain the active power are revisited, and for the first time, the commonly used simplified phenomenological Suzen–Huang model (SHM) is used for the computation of electrical characteristics. The SHM represents fair qualitative features of the starting vortex. However, it fails when time-resolved velocity profiles are compared. Results show that even with an optimized parametrical analysis of the “tuned” plasma variables, the model is not able to fully reproduce the induced wall-jet neither spatially nor temporally. Furthermore, it underestimates the power consumption by more than 80%. The intrinsic challenge of accurately measuring the alternating current of the DBD and the instantaneous mechanical power, together with the failure of representing time-resolved velocity profiles and the underestimated electric power by the model, highlights that a better phenomenological model including gas dynamics and electric characteristics or using a fully coupled physical plasma model is required.

Evaluation of Tribological and Mechanical Properties of Carbon Steel with Fluoroligomeric Film at Piezoelectric Actuator Contact

The tribological investigations of carbon steel surfaces modified with fluoroligomeric materials were performed. Compared with the uncoated steel, the fluoroligomeric coated surface showed higher plasticity of the modified surface in the scratch tests where the fluoroligomeric film was not destroyed by higher loading. This could be explained by the lower micro hardness of the steel after processing by fluoroligomer and the influence of the adsorbic Rebinder effect. This study includes original results of the loading influence on the efficiency of the piezoelectric actuator and the wear value of the frictional element, which is important explaining the greater longevity of the piezoelectric actuator. Fluoroligomer treatment of the surface considerably improved the performance of the piezoelectric actuator. Using the reference steel roller in the piezoelectric actuator under minimum loads was characterized by a decrease in rotor speed with increasing the pressing of the frictional element. When the rotor was coated by fluoroligomer, the speed remained stable when increasing the pressing force. Using the reference steel roller, the rotation after short-term overloads was not restored, and rollers with fluoroligomeric surface started to rotate soon as the short-term overload was removed. The higher efficiency of piezoelectric actuators with a fluoroligomeric layer on the roller is related to almost two times lower wear of a friction element operating with coated rollers as compared to reference rollers.

An ultrahigh efficiency electrochemical actuator

Electrochemical actuators (EAs) with capabilities of triggering large deformation are attracting great interests because of their low stimulation voltage and high durability. However, porous electrode structures (PESs) with either a large unexpected strain or small-size inserted ions lead to small actuation strain and low energy transduction efficiency. To address this problem, an ideal electrode material, namely, pyrolytic graphite (PG), with an anisotropic densely stacked electrode structure (ASES), was proposed, and the optimal insertion ion, namely, AlCl4− with a large radius, was selected. Simulations show that an ASES presents an increased actuation strain and effectively eliminates unexpected strain. In addition, the insertion of AlCl4− into the graphite layers can lead to a directionally large volume expansion (>230%) due to the low energy barrier and large ionic radius. Experimental results reveal that the PG can expand/contract repeatedly with a high linear strain of ≈48% under a zero stress and ≈32% under a load of 2.5 MPa. EAs based on PG and AlCl4− achieve excellent actuation efficiency with an energy density of 105.89 J cm −3, power density of 0.35 W cm−3 and a high electromechanical transduction efficiency of up to 14.30%. This design method provides a significant way to develop high-performance EAs.

Full-State-Constrained Non-Certainty-Equivalent Adaptive Control for Satellite Swarm Subject to Input Fault

Satellite swarm coordinated flight (SSCF) technology has promising applications, but its complex nature poses significant challenges for control implementation. In response, this paper proposes an easily solvable adaptive control scheme to achieve high-performance trajectory tracking of the SSCF system subject to actuator efficiency losses and external disturbances. Most existing adaptive controllers based on the certainty-equivalent (CE) principle show unpredictability and non-convergence in their online parameter estimations. To overcome the above vulnerabilities and the difficulties caused by input failures of SSCF, this paper proposes an adaptive estimator based on scaling immersion and invariance (I&I), which reduces the computational complexity while improving the performance of the parameter estimator. Besides, a barrier Lyapunov function (BLF) is applied to satisfy both the boundedness of the system states and the singularity avoidance of the computation. It is proved that the estimator error becomes sufficiently small to converge to a specified attractive invariant manifold and the closed-loop SSCF system can obtain asymptotic stability under full-state constraints. Finally, numerical simulations are performed for comparison and analysis to verify the effectiveness and superiority of the proposed method.

Novel SPECTA Actuator to Improve Energy Recuperation and Efficiency

The current state of the art in compliant actuation has already good performance, but this is still insufficient to provide a decent autonomy for the next generation of robots. In this paper, a next step is taken to improve the efficiency of actuators by tackling and enhancing the Series-Parallel Elastic Constant Torque Actuation (SPECTA) concept, which has previously been analyzed in simulations. In this work, the efficiency is increased further by decoupling the springs and their driving parts through the use of locking mechanisms, such that the motors are not always loaded and the springs can easily store energy from both input or output. Simulations have been performed to confirm this and they also showed that, in the SPECTA concept, it is always better to use high-speed motors instead of high-torque motors, even with non-efficient gearing. In this paper, the SPECTA concept is also validated experimentally with the use of a newly built test setup. In light of the obtained results, showing an increase in efficiency for almost all working points, it can be stated that SPECTA is a promising new actuation technology that allows for an increase in energy recuperation, efficiency, and autonomy.

Nonlinear burn control in ITER using adaptive allocation of actuators with uncertain dynamics

ITER will be the first tokamak to sustain a fusion-producing, or burning, plasma. If the plasma temperature were to inadvertently rise in this burning regime, the positive correlation between temperature and the fusion reaction rate would establish a destabilizing positive feedback loop. Careful regulation of the plasma’s temperature and density, or burn control, is required to prevent these potentially reactor-damaging thermal excursions, neutralize disturbances and improve performance. In this work, a Lyapunov-based burn controller is designed using a full zero-dimensional nonlinear model. An adaptive estimator manages destabilizing uncertainties in the plasma confinement properties and the particle recycling conditions (caused by plasma–wall interactions). The controller regulates the plasma density with requests for deuterium and tritium particle injections. In ITER-like plasmas, the fusion-born alpha particles will primarily heat the plasma electrons, resulting in different electron and ion temperatures in the core. By considering separate response models for the electron and ion energies, the proposed controller can independently regulate the electron and ion temperatures by requesting that different amounts of auxiliary power be delivered to the electrons and ions. These two commands for a specific control effort (electron and ion heating) are sent to an actuator allocation module that optimally maps them to the heating actuators available to ITER: an electron cyclotron heating system (20 MW), an ion cyclotron heating system (20 MW), and two neutral beam injectors (16.5 MW each). Two different actuator allocators are presented in this work. The first actuator allocator finds the optimal mapping by solving a convex quadratic program that includes actuator saturation and rate limits. It is nonadaptive and assumes that the mapping between the commanded control efforts and the allocated actuators (i.e. the effector model) contains no uncertainties. The second actuator allocation module has an adaptive estimator to handle uncertainties in the effector model. This uncertainty includes actuator efficiencies, the fractions of neutral beam heating that are deposited into the plasma electrons and ions, and the tritium concentration of the fueling pellets. Furthermore, the adaptive allocator considers actuator dynamics (actuation lag) that contain uncertainty. This adaptive allocation algorithm is more computationally efficient than the aforementioned nonadaptive allocator because it is computed using dynamic update laws so that finding the solution to a static optimization problem is not required at every time step. A simulation study assesses the performance of the proposed adaptive burn controller augmented with each of the actuator allocation modules.

Highly Efficient Fiber Optic Thermal Heating Device Based on Turn-Around-Point Long Period Gratings

The use of in-fiber core-to-cladding coupling components for thermal heating purposes has been well assessed in the last decades within the development of fiber optic devices for flow measurements and water thermal conductivity calculation. In these devices, light travelling in the fiber core is transferred into the cladding and absorbed by a metallic layer surrounding the fiber, with the consequent resistive heating generation. Here we demonstrate the use of a Turn-Around-Point (TAP) Long Period Grating (LPG) as resonant core-to-cladding light coupling mechanism for the fabrication of a highly efficient heating device based on metallic coated Fiber Bragg Grating (FBG). A properly designed TAP LPG was fabricated by means of point-to-point UV laser and spliced to a 150 nm thick Au-coated FBG. The heating efficiency characterization of the final device was analyzed, in both air and water, by evaluating the temperature increase in the gold layer surrounding the FBG at incremental values of the injected power. Collected results confirm that the use of LPGs involving the excitation of higher order cladding modes provides an excellent transferring mechanism of the fiber core light into the cladding, which in turn guarantees very high thermal heating efficiency to the final device. Moreover, by comparing such results with the performance of other in-fiber core-to-cladding coupling components already presented in literature, it was found that the TAP LPG-based device exhibits an actuation efficiency 2.5 times greater, thus resulting the most effective and highly performing solution for energy transfer to the metallic overcoat.

Adaptive output-Feedback asymptotic tracking control for a class of nonlinear systems with actuator failure

This study deals with the output-feedback asymptotic tracking control problem for a class of nonlinear strict-feedback systems with actuator loss of effectiveness failure. To handle with the output-feedback control issue in the presences of nonlinearities, a new reduced-order observer design is presented, by utilizing the dynamic gain technique, which not only eliminates the limitation that the Lipchitz coefficients are required to be known in the existing output-feedback results, but makes full use of the measurable information. Furthermore, a new failure compensation mechanism is proposed to erase the effect of actuator failure, by introducing a cubic absolute-value Lyapunov function method and a novel (σ,σf)-modification technique. Compared with the existing output-feedback failure compensation results, our proposed method can not only relax the assumption requirement on nonlinear function, i.e., the nonlinear function with respect to output y can be extended to the nonlinear one with respect to state variable χ¯i in the means of asymptotic tracking, but also avoid the issue that the estimate for actuator efficiency indicator drifts to a large value suddenly. Further, within the framework of backstepping design, a new high-gain reduced-order observer based adaptive output-feedback failure compensation control is developed. Then, with the aid of Lyapunov analysis method, it is shown that all the signals in the closed-loop system are globally bounded, and the system output can asymptotically track a given reference signal. Finally, a simulation example is given to illustrate the efficiency of the proposed techniques.

Motor unit buckling in variable recruitment fluidic artificial muscle bundles: implications and mitigations

Fluidic artificial muscles (FAMs) are a popular actuation choice due to their compliant nature and high force-to-weight ratio. Variable recruitment is a bio-inspired actuation strategy in which multiple FAMs are combined into motor units that can be pressurized sequentially according to load demand. In a traditional ‘fixed-end’ variable recruitment FAM bundle, inactive units and activated units that are past free strain will compress and buckle outward, resulting in resistive forces that reduce overall bundle force output, increase spatial envelope, and reduce operational life. This paper investigates the use of inextensible tendons as a mitigation strategy for preventing resistive forces and outward buckling of inactive and submaximally activated motor units in a variable recruitment FAM bundle. A traditional analytical fixed-end variable recruitment FAM bundle model is modified to account for tendons, and the force–strain spaces of the two configurations are compared while keeping the overall bundle length constant. Actuation efficiency for the two configurations is compared for two different cases: one case in which the radii of all FAMs within the bundle are equivalent, and one case in which the bundles are sized to consume the same amount of working fluid volume at maximum contraction. Efficiency benefits can be found for either configuration for different locations within their shared force–strain space, so depending on the loading requirements, one configuration may be more efficient than the other. Additionally, a study is performed to quantify the increase in spatial envelope caused by the outward buckling of inactive or low-pressure motor units. It was found that at full activation of recruitment states 1, 2, and 3, the tendoned configuration has a significantly higher volumetric energy density than the fixed-end configuration, indicating that the tendoned configuration has more actuation potential for a given spatial envelope. Overall, the results show that using a resistive force mitigation strategy such as tendons can completely eliminate resistive forces, increase volumetric energy density, and increase system efficiency for certain loading cases. Thus, there is a compelling case to be made for the use of tendoned FAMs in variable recruitment bundles.

Ionic covalent organic framework based electrolyte for fast-response ultra-low voltage electrochemical actuators

Electrically activated soft actuators with large deformability are important for soft robotics but enhancing durability and efficiency of electrochemical actuators is challenging. Herein, we demonstrate that the actuation performance of an ionic two-dimensional covalent-organic framework based electrochemical actuator is improved through the ordered pore structure of opening up efficient ion transport routes. Specifically, the actuator shows a large peak to peak displacement (9.3 mm, ±0.5 V, 1 Hz), a fast-response time to reach equilibrium-bending (~1 s), a correspondingly high bending strain difference (0.38%), a broad response frequency (0.1–20 Hz) and excellent durability (>99%) after 23,000 cycles. The present study ascertains the functionality of soft electrolyte as bionic artificial actuators while providing ideas for expanding the limits in applications for robots.

The fault-tolerant consensus strategy for leaderless Multi-AUV system on heterogeneous condensation topology

The present paper proposes a distributed fault-tolerant consensus control protocol strategy for leaderless multi-autonomous underwater vehicle (AUV) systems, where actuators have a partial break-down. Instead of the global information, this strategy applies the relative state of the topology. Also, the topology graph can be any heterogeneous condensation digraph with a spanning tree in the communication network. The linear feedback technique is used to linearize the system model into a second-order multi-AUV system. Then, the Lyapunov functional method is used to prove the system's stability and astringency and the algorithm's effectiveness is simulated numerically. It was found that the actuator efficiency could not be the same in each AUV. Also, the partial actuator loss of effectiveness faults is more typical and complicated. In addition, each AUV's state can converge to the same asymptote, and the consensus error can converge to zero.