Actuation Efficiency Research Articles

Adaptive sliding mode control for stochastic jump systems against sensor and actuator failures

This study investigates the fault-tolerant control problem in the presence of simultaneous actuator degradation and additive sensor fault for a class of stochastic Markovian jump systems, where external disturbance and partially accessible mode information are considered. A new adaptive observer approach is developed to generate the asymptotic estimations of system state, unknown actuator efficiency factor and additive sensor fault. An adaptive sliding mode control law based on the state estimation is proposed to stabilise the resulting closed-loop fault system. Finally, an example of a linearised model of an F-404 aircraft engine system is presented to illustrate the effectiveness of the proposed control method.

Effect of nanosecond-pulsed plasma actuation on a separated laminar flow

An experimental investigation was carried out on the effect of unsteady periodic control on a separated laminar shear layer. Time resolved Particle Image Velocimetry (tr-PIV) was used to characterize a backward-facing step (BFS) flow (Reh=3600), periodically perturbed by a nanosecond Dielectric Barrier Discharge (ns-DBD) plasma actuator. Ensemble averaged vector fields indicate a decrease of reattachment length with increasing actuation non-dimensional frequency, reaching a minimum at a Sth=0.32. Further increase of forcing non-dimensional frequency, up to 0.4, resulted into an increase of the reattachment length, which nevertheless remained shorter than the non-actuated case. Spectral analysis of the fluctuating fields revealed a change of the amplified frequency range for the actuated cases with respect to the base flow. Proper Orthogonal Decomposition (POD) analysis showed that actuation leads to a redistribution of energy among coherent spatial modes. Stability diagrams were calculated from mean velocity field data for each case via Linear Stability Theory (LST). Results indicate that stability of each actuated case changes with respect to the non-actuated case. Moreover, looking into the calculated growth rate for all the cases a more stable flow regime is observed for the cases of most successful reduction in terms of reattachment length. The effect of a pulsed periodic perturbation on the control of a laminar shear layer promotes the development of large structures, i.e. K-H vortices, due to inviscid-viscous interaction. These convect downstream resulting in a mean flow deformation (MFD) which causes a change of stability. New unstable frequencies are excited and promote the redistribution of energy among modes. This ultimately affects the efficiency of actuation in promoting transition from laminar to turbulent flow.

Piezoelectric MEMS resonators based on ultrathin epitaxial GaN heterostructures on Si

We present the first results for microelectromechanical (MEMS) resonators fabricated on epitaxial nitride semiconductors with thin buffers engineered for MEMS and NEMS applications. These results are used to assess the use of thin buffers for GaN MEMS fabrication. On a 700 nm thick AlGaN/GaN epilayer, a high tensile stress is observed to increase the resonant frequency. The electromechanical coupling efficiencies of integrated transducers are assessed and compared with previously obtained results on commercially available 2 µm thick epilayers used for power transistor applications. A 28 nm V−1 actuation efficiency is measured on the 700 nm thick structure which is slightly better than the one measured on the 2 µm buffer. The electrical response of a gateless detector designed as a piezoresistance is obtained and a gauge factor of 60 is estimated. These results show that material issues can be unlocked to exploit the potentialities of III-nitrides for NEMS applications.

A robust adaptive nonlinear fault-tolerant controller via norm estimation for reusable launch vehicles

In this paper, a reusable launch vehicle (RLV) attitude control problem with actuator faults is addressed via the robust adaptive nonlinear fault-tolerant control (FTC) with norm estimation. Firstly, the accurate tracking task of attitude angles in the presence of parameter uncertainties and external disturbances is considered. A fault-free controller is proposed using dynamic surface control (DSC) combined with fuzzy adaptive approach. Furthermore, the minimal learning parameter strategy via norm estimation technique is introduced to reduce the multi-parameter adaptive computation burden of fuzzy approximation of the lump uncertainties. Secondly, a compensation controller is designed to handle the partial loss fault of actuator effectiveness. The unknown maximum eigenvalue of actuator efficiency loss factors is estimated online. Moreover, stability analysis guarantees that all signals of the closed-loop control system are semi-global uniformly ultimately bounded. Finally, illustrative simulations show the effectiveness of the proposed method.

Thermal behavior modeling and characteristics analysis of electrothermal microactuators

Electrothermal microactuators possess a number of desirable attributes including ease of fabrication and large force and displacement capabilities relative to other types of microactuators, but these performances come at the expense of large input energy and relatively low frequencies because of the time necessary to reach thermal equilibrium. These characteristics provide motivation for improving thermal actuator designs that are more energy efficient and better suited for high-frequency applications. To this end, models describing the combined electrothermal and thermomechanical behavior of thermal actuators are developed in this thesis. The temperature distribution of the actuator is analyzed and the influence of the actuator’s geometrical parameters on its force and displacement is studied. Steady-state and transient thermal responses of the actuator operating in air and a vacuum are investigated by creating finite-difference model with temperature-dependent parameters, this model allows temperatures throughout the actuator to be simulated as a function of time. Results demonstrate that the efficiency of the actuator can be improved significantly by operating in a vacuum environment and providing short-duration, high-current pulse inputs. A set of parametric studies and design changes are evaluated through thermomechanical models, strategies gained from modeling analysis result in significant improvements in operational efficiency of the thermal actuator.

Improvement of Magnetic Actuator Capable of Movement on Magnetic Substance

In recent years, periodical inspection of large structures, such as large steel bridges with main towers of over 200 m, has been necessary. However, robots capable of a reciprocating movement over a long range have not been established yet. In this paper, a propulsion module with a bobbin-type electromagnet to increase the magnetic force was proposed. By changing the magnetic circuit, the experimental result demonstrates that the maximum efficiency of the magnetic actuator is 36.2% and the maximum pulling power is $\sim 1.5$ N. Furthermore, consideration of reciprocating movement by using two mass–spring models was given. The actuator system was capable of reciprocating movement with almost the same movement properties when powered by the same input power.

Synergistic effects of carboxylic acid-functionalized carbon nanotube and nafion/silica nanofiber on electrical actuation efficiency of shape memory polymer nanocomposite

Synergistic effects of self-assembled carboxylic acid-functionalized carbon nanotube (CNT) and nafion/silica nanofiber on the electro-activated shape recovery behavior of shape memory polymer (SMP) nanocomposite were investigated. Carboxylic acid-functionalized CNTs were self-assembled onto the carbon fiber mat to enhance their bonding reliability and achieve efficient electrical actuation for SMP matrix. Nafion/silica nanofibers were electrospun onto surfaces of the carbon fiber mat to prevent electrically resistive heat dissipation. The combination of electrically/thermally conductive CNTs and thermally resistive nafion/silica nanofibers results in improvement for both electrically induced shape recovery and actuation efficiency in the SMP nanocomposite.

Preliminary design and multi-objective optimization of electro-hydrostatic actuator

Electro-hydrostatic actuator is generally regarded as the preferred solution for more electrical aircraft actuation systems. It is of importance to optimize the weight, efficiency and other key design parameters, during the preliminary design phase. This paper describes a multi-objective optimization preliminary design method of the electro-hydrostatic actuator with the objectives of optimizing the weight and efficiency. Models are developed to predict the weight and efficiency of the electro-hydrostatic actuator from the requirements of the control surface. The models of weight prediction are achieved by using scaling laws with collected data, and the efficiency is calculated by the static energy loss model. The multi-objective optimization approach is used to find the Pareto-front of objectives and relevant design parameters. The proposed approach is able to explore the influence of the level length of linkage, displacement of pump and torque constant of motor on the weight and efficiency of the electro-hydrostatic actuator, find the Pareto-front designs in the defined parameter space and satisfy all relevant constraints. Using an electro-hydrostatic actuator for control surface as a test case, the proposed methodology is demonstrated by comparing three different conditions. It is also envisaged that the proposed prediction models and multi-objective optimization preliminary design method can be applied to other components and systems.

Frictional resistance model for tissue-capsule endoscope sliding contact in the gastrointestinal tract

Wireless capsule endoscopes are becoming prevalent in the medical field as screening, diagnostic and therapeutic tools within the gastrointestinal (GI) tract. However, state-of-the art capsules lack active locomotion systems, which could improve accuracy and broaden applications. The actuation efficiency for direct capsule-tissue contact depends on the frictional resistance between the capsule and the intestinal wall. A model for predicting the resistance force on a capsule was developed and experimentally validated by performing drag force experiments using various cylindrical capsule design parameters and tissue properties. Of the design parameters studied, capsule edge radius influences frictional resistance the most. The average normalized root-mean-square error between the model and experimental results is 6.25%. These results could lead to optimized capsule endoscope actuation systems.

Photo-thermo-mechanically actuated liquid crystalline elastomer nanocomposite reinforced by polyurethane fiber-network

ABSTRACTIn this work, we develop a nanocomposite consisting of nematic liquid crystal elastomer (LCE) matrix incorporated with single-wall carbon nanotubes (SWCNTs) and the reinforcement phase of polyurethane fiber-network (PUFN). The photo-thermo-mechanical actuation of LCE matrix is realized by converting light into heat with assistant of SWCNTs. The PUFN enhances the mechanical properties of the material, thus the actuation capability. Under the irradiation from a wide-spectrum light source with an intensity on the order of 100 mW/cm2, the PUFNs/SWCNT/LCE nanocomposite contracts up to 27% of the original length in several seconds due to the photo-induced strain, and recovers to the original length in several seconds after the light source is switched off. The efficiency of actuation is not light-spectrum dependent. The maximum effective actuation force is about 260 kPa, much larger than that of the LCE material without the reinforcement of PUFNs. The tensile strength and the performance of anti-fatigue failure under multiple reversible actuations are also greatly improved. The mechanism of the actuation capability of LCE material involved in the fiber-network reinforcement phase is studied.

Design and testing of a pulley and cable actuator for large ball valves

The objective of this work is the development of an innovative actuator for Velan ABV S.p.A., which is mainly used for control and special on/off applications where high efficiency and linear behaviors are desirable specifications. The main performances of the proposed actuator, which has been protected by a patent, have been compared with a conventional scotch yoke one, using both the simulation results and the experimental data. In order to measure the efficiency and the dynamical response of the actuators, the authors have designed a hydraulic test rig, configured to fulfill different testing procedures. In this way, it is possible to perform both static tests to identify actuator efficiency and dynamic hardware-in-the-loop tests in which an assigned load or valve impedance function is simulated to verify the response of the tested object in realistic operating conditions. Finally, the proposed test rig has been successfully used to perform reliability and fatigue tests in which the actuator is stressed with realistic and repetitive loads. Moreover, the integrated development of both innovative actuator and testing devices is explained introducing interesting concepts whose applications are normally limited to robotics (e.g. impedance and force control) or vehicular technology (e.g. smart suspensions and suppression of vibrations).

Experimental Estimation of SparkJet Efficiency

The results presented herein include SparkJet characterization studies with a focus on understanding the actuator efficiency during stage 1 and the resulting flowfield. Experimental cavity pressure and arc power measurements are used to estimate efficiency whereas experimental microschlieren images are used to visualize the flowfield and quantify the velocity of distinct flow features. The experimental measurements used to estimate efficiency during stage 1 of a single SparkJet cycle were acquired using a single orifice SparkJet design in a quiescent environment. The experiments evaluated efficiency as a function of cavity volume (), orifice diameter (0.4–2.0 mm), and input energy (0.17–0.77 J per pulse). The results show that efficiency is a function of parasitic resistance in circuit components, high-temperature gas dynamics, and the ratio of input energy to internal energy of the cavity air, . The circuit design used here was approximately 80% efficient and the pressure-based efficiency decreased from 40 to 20% as increased from 5 to 60. Adjusting the pressure-based efficiency calculation to be a function of the measured arc energy, the conversion from arc energy to the energy available to raise the cavity pressure was 40–45% efficient. Using a SparkJet four-orifice array design (cavity volume of and each orifice 0.4 mm in diameter) in a quiescent environment, phase-averaged microschlieren images of a single SparkJet cycle reveal the rapid flow development when the first evidence of flow is seen after the SparkJet initiation and a well-developed jet is visible by . Also based on these calibrated images, the maximum jet velocity was estimated at .

Performance and efficiency of loudspeaker driven synthetic jet actuator

The paper presents the results of a detailed experimental investigation wherein the efficiency of synthetic jet actuator, momentum velocity, Reynolds number and input power as a function of oscillating actuator frequency and for different cavity configuration are studied. Synthetic jet actuator consists of plexiglas cavity and a loudspeaker. We have proposed synthetic jet actuator efficiency definition as a ratio of flow kinetic power based on momentum velocity to electrical power feeding generator. The maximum achieved efficiency is about 5%, although with another loudspeaker the efficiency would be different. Experimental investigation was carried out for the Reynolds number in range Re=0–22,600 and for the Stokes number St=13–308. We find out that the maximum efficiency appears close to resonant loudspeaker frequency or Helmholtz frequency. It depends on geometrical configuration of the actuator. Presented results may be useful for designing loudspeaker driven synthetic jet actuator.

Performance study of a hydrogen powered metal hydride actuator

A thermally driven hydrogen powered actuator integrating metal hydride hydrogen storage reactor, which is compact, noiseless, and able to generate smooth actuation, is presented in this article. To test the plausibility of a thermally driven actuator, a conventional piston type actuator was integrated with LaNi5 based hydrogen storage system. Copper encapsulation followed by compaction of particles into pellets, were adopted to improve overall thermal conductivity of the reactor. The operation of the actuator was thoroughly investigated for an array of operating temperature ranges. Temperature swing of the hydride reactor triggering smooth and noiseless actuation over several operating temperature ranges were monitored for quantification of actuator efficiency. Overall, the actuator generated smooth and consistent strokes during repeated cycles of operation. The efficiency of the actuator was found to be as high as 13.36% for operating a temperature range of 20 °C–50 °C. Stress–strain characteristics, actuation hysteresis etc were studied experimentally. Comparison of stress–strain characteristics of the proposed actuator with traditional actuators, artificial muscles and so on was made. The study suggests that design modification and use of high pressure hydride may enhance the performance and broaden the application horizon of the proposed actuator in future.

Design and Testing of an Innovative Wire Transmission for a Quarter-Turn Actuator

The object of this work is the development of an innovative wire actuator in collaboration with Velan ABV S.p.A., which will be mainly used in applications in which high efficiency and linear behavior are desirable specifications. In this work, the main features of the proposed actuator, which is protected by a patent, are evaluated and compared with respect to a conventional solution consisting of a scotch yoke (SY) transmission system. The comparison is performed using both the simulation results and the experimental data. In order to identify the efficiency and the dynamical response of the innovative actuator, the authors have designed a hydraulic test rig, which can be configured to perform different testing procedures. In this way, it is possible to perform both static tests to identify actuator efficiency, and dynamic ones, in which an assigned load or a valve impedance function is simulated to verify the response of the tested actuator in realistic conditions. Finally, the proposed test rig has been successfully employed to perform both reliability and fatigue tests in which the actuator is subjected to realistic and repetitive loads.

A New Type of Hydraulic Muscle

This paper presents the invention and development of a new fundamental type of hydraulic actuator, aimed at delivering better actuation efficiency. This actuator is a flexible tube, composed of two different materials, which deflects while applying inner pressure. This concept is simple to produce, and allows adaptation of the deflected shape by the design parameters (radius, wall thickness, geometry, etc.). Among other applications, it is mostly suitable for the activation of fins of nature-like marine robots. Theoretical formulation, production of prototypes and actuation experiments are presented, as well as material hysteresis research and an application example.

伸縮バルーンアクチュエータの出力変換効率の向上

In this paper, we report improvement of a contracting motion balloon actuator for output enhancement conversion efficiency. A contracting motion balloon actuator composed of two polyimide films and a PBA. A contracting motion balloon actuator converts from swelling motion to contracting motion by using a pantograph mechanism. However, a contracting motion balloon actuator could not convert completely from swelling motion to contracting motion since polyimide films did not touch whole balloon of a PBA. In this work, we increase areas which touch between polyimide films and balloon of a PBA. We proposed to improve output conversion efficiency of a contracting motion actuator by increasing the areas.

Distributed fault-tolerant control for a class of cooperative uncertain systems with actuator failures and switching topologies

This paper studies the distributed fault-tolerant control (DFTC) problem for a class of high-order multi-agent systems (MASs) with switching undirected topologies, heterogeneous matching uncertainties, disturbances and actuator faults including loss of effectiveness, bias, outage and stuck. In this frame work, the communication network of dynamic agents may switch among several undirected connected graphs. It is assumed that the actuator efficiency factors, the lower and upper bounds of the time-varying failures and heterogeneous uncertainties, disturbances and the leader’s control input signal, are unknown. Based on the relative information of neighbors, a novel fault-tolerant consensus tracking protocol is designed for each follower node via distributed adaptive mechanism. By utilizing the multiple Lyapunov functions method and algebraic graph theory, a sufficient condition for consensus tracking is established. Furthermore, it is proved that if the topology dwell time is larger than a positive threshold, the state of each follower node synchronizes to that of the leader with a bounded residual error in the presence of actuator faults, heterogeneous matching uncertainties and disturbances. Finally, two numerical examples are given to show the effectiveness of the proposed control scheme.

Electromechanical characteristic analysis of a dielectric electroactive polymer (DEAP) actuator

To assist in the design and optimization of dielectric electroactive polymer (DEAP) actuators, an analytical model for the electromechanical response of cone DEAP actuators is developed. Using the Yeoh form strain energy potential and the Maxwell stress tensor, the constitutive relationship of the DEAP that accounts for the electromechanical coupling behavior is deduced. The equilibrium equations of DEAP actuators with a cone configuration are derived and an analytical model is then proposed. With this model, the actuation characteristics of the DEAP actuator, including actuation displacement, force output and efficiency can be calculated. Additionally, the principal stresses and principal stretch ratio of the membrane under different actuation voltages can be determined, along with the wrinkling failure mode of DEAP actuators. The experimental results for the DEAP actuator matched the numerical results determined using the proposed model. As such, the proposed work is beneficial as a guide for the design optimization of DEAP actuators.

Modelling of efficiency of synthetic jet actuators

A comprehensive and detailed modelling to evaluate the efficiency of energy conversion of piezo-electric actuators driving synthetic jets is developed. The contribution is original because the analysis is based on the energy equations of the two coupled oscillators, the membrane and the acoustic one, which are directly derived from the corresponding motion equations. The modelling is validated against numerical as well as experimental investigations carried out on home-made actuators having brass and aluminum shims on which the piezo-disk is bonded. A major result is that for aluminum shim the global efficiency (representing the conversion of input Joule power to kinetic power) decreases with increasing the applied voltage. Another finding is that the conversion process of mechanical power transferred, by means of the driving membrane, to Helmholtz oscillator kinetic power scales dramatically with the coupling degree of the oscillators. The coupling degree influences the efficiency of two cavities actuators sharing the same piezo-diaphragm as well. Considerations are reported to relate the theoretical orifice efficiency to the practical jet efficiency issuing in the external field.