Large Actuation Research Articles

Failures Mapping for Aircraft Electrical Actuation System Health Management

This paper presents the different types of failure that may occur in flight control electrical actuation systems. Within an aircraft, actuation systems are essential to deliver physical actions. Large actuators operate the landing gears and small actuators adjust passenger seats. As developing, aircraft systems have become more electrical to reduce the weight and complexity of hydraulic circuits, which could improve fuel efficiency and lower NOx emissions. Electrical Actuation (EA) are one of those newly electrified systems. It can be categorized into two types, Electro-Hydraulic Actuation (EHA) and Electro-Mechanical Actuation (EMA) systems. Emerging electric and hydrogen fuel aircraft will rely on all-electric actuation. While electrical actuation seems simpler than hydraulic at the systems level, the subsystems and components are more varied and complex. The aim of the overall project is to develop a highly representative Digital Twin (DT) for predictive maintenance of electrical flight control systems. A comprehensive understanding of actuation system failure characteristics is fundamental for effective design and maintenance. This research focuses on the flight control systems including the ailerons, rudders, flaps, spoilers, and related systems. The study uses the Cranfield University Boeing 737 as the basis to elaborate the different types of actuators in the flight control system. The Aircraft Maintenance Manual (AMM) provides a baseline for current maintenance practices, effort, and costs. Equivalent EHA and EMA to replace the 737 systems are evaluated. In this paper, the components and their failure characteristics are elaborated in a matrix. The approach to model these characteristics in DT for aircraft flight control system health management is discussed. This paper contributes to the design, operation and support of aircraft systems.

Biocatalytic 3D Actuation in Liquid Crystal Elastomers via Enzyme Patterning.

Liquid crystal elastomers (LCEs) are stimuli-responsive materials that undergo large shape transformations after undergoing an order-disorder transition. While shape reconfigurations in LCEs are predominantly triggered by heat, there is a considerable interest in developing highly specific triggers that work at room temperature. Herein, we report the fabrication of biocatalytic LCEs that respond to the presence of urea by covalently immobilizing urease within chemically responsive LCE networks. The hydrogen-bonded LCEs developed in this work exhibited contractile strains of up to 36% upon exposure to a base. Notably, the generation of ammonia by immobilized urease triggered a disruption in the supramolecular network and a large reduction of liquid crystalline order in the films when the LCEs were exposed to urea. This reduction in order was macroscopically translated into a strain response that could be modulated by changing the concentration of urea or exposure time to the substrate. Local control of the mechanical response of the LCE was realized by spatially patterning the enzyme on the surface of the films. Subsequent exposure of enzymatically patterned LCE to urea-triggered 3D shape transformations into a curl, arch, or accordion-like structure, depending on the motif patterned on the film surface. Furthermore, we showed that the presence of salt was critical to prevent bridging of the network by the presence of ammonium ions, thereby enabling such macroscopic 3D shape changes. The large actuation potential of LCEs and the ability to translate the biocatalytic activity of enzymes to macroscopic 3D shape transformations could enable use in applications ranging from cell culture, medicine, or antifouling.

Adaptive solar panel - overview and conceptual design

Renewable energy should reach its maximum usage capacity, around 20%, by 2025, as laid out by the Malaysian government to achieve the seventh Sustainable Development Goals (SDG): Affordable and clean energy. Many actions have been implemented to support the idea, including the development of solar energy panels in large photovoltaic installation. However, the installations require a wide area of land, and the efficiency offered is limited due to their fixed position. The efficiency of solar panels in absorbing the light from the sun is important to increase the energy supply. Several designs of the adaptive solar panel were developed by researchers, but the installation costs are high due to the components used. Commonly used actuators to move the solar panels are motor (DC motor, stepper motor, servo motor) that actuate according to the signals from photosensor, programming logic control (PLC), or microcontroller. Herein, the development of an Adaptive Solar Panel (ASP) is studied. SMA with high recoverability when it is strained is introduced as an actuator that capable of generating large actuation when heated to move the solar panel. In discovering the potential of SMA wire, a modern environmental-friendly design with six layers of solar panels with a rotational support system was designed in this study. In future work, the SMA wire actuation will be evaluated by computational simulation method using LS-Dyna.

Defects dipoles control strategy for temperature-insensitive piezoelectricity in the lead-free BiFeO3-BaTiO3 ceramics

The large and temperature-insensitive piezoelectric actuator coefficient (d33*) with small strain hysteresis and the enhanced piezoelectric sensor coefficient (d33) with high Curie temperature (TC) are highly demanded in the real applications. The controlled design of defects engineering has been proved to be an effective way for the improvement of temperature strain stability (Δd33*(T)) and reducing hysteresis (Hs) in piezoelectric ceramics. Two types of defect dipoles such as (FeFe3+2+′ −VO2−••) and (VBi3+''' −VO2−••) are possible in the lead-free BiFeO3–BaTiO3 (BF-BT) ceramics that suppress their functional property. However, these defect dipoles can be inhibited in the Ba2+-site Sm3+-donor BF-BT engineered ceramics. Additionally, the valence and ionic radius difference of Sm3+ (1.24 Å) and Ba2+ (1.61 Å) becomes the origin of large lattice strain in the unit cell of BF-BT that leads to the maximum piezoelectric performance. Therefore, the enhanced d33 (334 pC/N) and d33* (552 pm/V) with high TC (454 °C) were obtained in the Ba2+-site Sm3+-donor BF-BT lead-free ceramics. Furthermore, the reduced Hs ≈ 18% and preferable temperature-insensitive piezoelectric strain, Δd33*(T) ≈ 10% in the temperature 25–125 °C are highly encourageable in the lead-free ceramics. Hence, the defect dipoles controlling strategy helps to improve the functional properties and the concept presented here can be applied to design the lead-free piezoelectric material for real applications.

Thermally induced self-rupture of a constrained liquid crystal elastomer

Liquid crystal elastomer (LCE) is a promising soft material which exhibits large actuation and can respond to different external fields with proper modifications. In the case of thermally actuated LCEs, the fracture properties are crucial to ensure that LCEs can robustly function under different loading and heating conditions, without unexpected failure. In this work, we systematically characterize the fracture energy of LCE at different temperatures and loading rates. We found that LCE behaves like a tough elastomer at low temperatures and high loading rates, but the fracture energy dramatically drops once LCE is heated beyond the nematic to isotropic transition temperature (TNI). At high temperatures, a constrained precut LCE sample can undergo self-rupture due to the large actuation stress. We have also used the measured fracture energy to successfully predict the critical temperature of self-rupture for different sample geometries.

A novel large stepping-stroke actuator based on the bridge-type mechanism with asymmetric stiffness

This paper presents the design, analysis, and experiments of a novel stick–slip actuator with large working stroke and high resolution based on parasitic motion. To meet the requirement on large stepping-stroke in the fields of nanofabrication and nano-characterization, the bridge-type mechanism with asymmetric stiffness which changes the distribution of piezoelectric actuator elongation at two input points is proposed. A chain-based compliance matrix model is established for the static performance characterization and parameter optimization of the dual-input closed-loop compliant mechanism, and the performance is further studied by finite element method. The prototype of the proposed actuator is manufactured and experimental tests are conducted to investigate its characteristics. The results indicate that the maximum motion speed is 23.53 mm/s with the driving frequency of 350 Hz. The stepping-stroke is 102 μm, and the resolution is measured to be 12 nm. It is confirmed that the proposed actuator is feasible to enlarge the stepping-stroke and work stably.

Fracture Toughness and Blocking Force of Temperature-Sensitive PolyNIPAAm and Alginate Hybrid Gels.

In the field of actuator materials, hydrogels that undergo large volume changes in response to external stimuli have been developed for a variety of promising applications. However, most conventional hydrogels are brittle and therefore rupture when they are stretched to moderate strains (~50%). Thus, gels to be used for actuators still require improved mechanical properties and actuation performance. In this study, we synthesized a tough and thermo-sensitive hydrogel with a large actuation force by forming interpenetrating networks between covalently crosslinked poly(N-isopropylacrylamide) and ionically crosslinked alginate. Poly(N-isopropylacrylamide) was used as a thermo-sensitive actuation material, and alginate was found to enhance the mechanical properties of the hydrogels. Due to the enhanced elastic modulus and energy dissipation in the hybrid gel, the toughness was increased by a factor of 60 over that of pure PNIPAAm gel. Further, based on the results showing that the hybrid gel exhibits an actuation force that is seven times higher than that of pure PNIPAAm gel, the hybrid gel is more applicable to real actuators.

Large amplitude vibration of a cantilever actuated by a high-frequency pulsed laser.

Laser excitation based on the thermoelastic principle is effective for micro-scale actuation, enabled energy conversion from optical to mechanical. The major advantages lie in non-contact actuation, easy miniaturization, and integration. To avoid surface damage, the laser power per unit is limited, leading to several micrometers of the vibration. In this study, a pure nickel millimeter-sized cantilever is successfully actuated at a low-frequency resonance (around Hz) via a nanosecond pulsed laser. By modal interaction, the energy is transferred from a low-intensity, high-frequency (around kHz) excitation to a low-frequency response with millimeter amplitude. The stable low-frequency resonance of the cantilever was maintained by changing the laser pulse parameters and the illumination locations. We also present a method to control the vibration of the cantilever using a modulated wave (MW: the laser wave modulated by a rectangular wave). The cantilever's amplitude can be efficiently adjusted by changing the laser power or duty cycle of the MW. The resonance frequency of the cantilever also can be altered by optimizing the geometries to meet various actuation requirements. This study enables large actuation (up to tens of millimeters) by laser excitation, facilitating applications in precision manipulation, microfluidic mixing, lab-on-a-chip device, and other related micro actuation devices.

A user-configurable electric actuator hybrid test platform: Development and applications for viscoelastic damping system seismic testing

To expand the inclusiveness of hybrid test platform research, enhance the flexibility of hybrid test platforms using various control strategies, and promote the development of hybrid test techniques, a low-cost user-configurable electric actuator hybrid test platform is established in this paper. This platform can be transferred to other medium or large electric actuator hybrid test platform, the research applications of this platform cannot be limited by their proposed setup. Firstly, the hardware system design including hybrid test facility integrated control system core architecture and all related signal routings are carried out. Then, the improved equivalent force control feedback method based on force-loading control is proposed, and the software system development including hybrid test process control system software and user-configurable STM32 microcontroller (UCSM) software are conducted. Next, the mechanical performance of viscoelastic damper is tested, and the mechanical model parameters of viscoelastic damper are regressed. The accuracy of electric actuator force control (inner control loop), of which the control tasks get executed on the UCSM is verified using the experimental substructure of viscoelastic damper. The hybrid test of viscoelastic damping system verifies the reliability and robustness of hybrid test platform (outer control loop). Finally, the developed hybrid test platform implements various hybrid tests of viscoelastic damping system under broad temperature range and different seismic intensities. The test results reveal the influence of temperature and seismic intensities on the seismic control effect of viscoelastic damper.

Adaptive Fault-tolerant and Anti-disturbance Attitude Control of the Reconfigurable Modular CubeSat

This paper addresses the dynamical coupling and attitude control problems caused by the large-scale abrupt changes of the system mass characteristics and the relative motion of the sub-body during the autonomous reconfiguration of the modular satellite in orbit, the attitude dynamics equations of the reconfigurable modular CubeSat system with time-varying mass characteristics parameters are derived. An improved adaptive fault-tolerant anti-disturbance control algorithm that does not rely on an accurate dynamics model and converges quickly in finite time is also proposed based on the composite control idea. In the attitude control of modular CubeSat with large external disturbances and large range of moment of inertia time variation, the method has a faster convergence speed and higher accuracy than the traditional sliding mode control. Without any fault detection and diagnostic information, the method is able to achieve fast and highly accurate attitude adaptive fault-tolerant control in the presence of large disturbances and actuator time-varying, stochastic-type faults through real-time observation of total disturbances inside and outside the system. The final simulation results verify the effectiveness and reliability of the method.

Experimental analysis of fiber-reinforced laminated composite plates with embedded SMA wire actuators

Shape memory alloy (SMA) wires are effective smart actuators since they provide relatively large actuation force and strain in a very limited space. Embedding SMA wires in flexible laminated composite plates or shells allows for creating active structures for morphing applications. However, the design of such structures is challenging due to the nonlinear thermomechanical coupling of SMA materials, the adhesion of the SMA actuators to the resin, the effect of temperature on the adhesion strength, the heat transfer between the SMA wires and the surrounding laminate, and the convection boundary conditions. This paper presents an experimental analysis of smart fiber-reinforced composite laminated plates with embedded SMA wires, focusing on the relationship between the applied electric current, measured temperature of the SMA wires, and the resulting tip deflection. A temperature-based control method was developed to achieve the required wire temperature and tip deflection as quickly as possible. Results showed that the fiber-orientation angle of the composite plies and the convection boundary conditions have significant effects on the structure’s actuation. With cyclic actuation, damage starts around the heated SMA wires and can grow to cause delamination at areas between neighboring SMA wires and yielding of the matrix material, resulting in permanent deformation.

Heterogeneous Multi-Agent-Based Fault Diagnosis Scheme for Actuation System

In this paper, a fault diagnosis method of a heterogeneous multi-agent is proposed that realizes the rapid and accurate fault diagnosis of a redundant multi-type actuation system of large aircraft. Firstly, the multi-agent model of a large aircraft actuation system is established, the composition of the actuation system and the relationship between each multi-agent are clarified and three different types of actuator mathematical models are established. Secondly, a fault detection and isolation (FDI) model is established and transformed into an optimization problem according to different performance index requirements. Aiming at the optimization problem, combined with the principle of linear matrix inequality (LMI), the fault diagnosis algorithm of a heterogeneous multi-agent system is designed. Moreover, the threshold judgment method based on the error signal is presented. Finally, the three actuator models of the aileron actuation system of large aircraft are combined to complete the fault diagnosis of a heterogeneous multi-agent system under the given model interference and model fault. The obtained results demonstrate and validate that the proposed method can accurately and effectively diagnose the faults of the actuator and its associated actuators.

The electrical response and self-sensing of the fully flexible PVC gel actuator based on flexible electrodes

There has recently been a substantial increase in interest in research on PVC gel actuators because of its numerous advantages over traditional actuators, such as low mass density, large actuation strain, great compliance, and simple manufacturing. However, the current PVC gel actuator is mainly based on the research of rigid electrodes, and there are few researches based on flexible electrodes. In this paper, a fully flexible actuator based on PVC gel film and carbon grease electrode has been prepared. The mechanical properties of the prepared PVC gels with different plasticizer ratios were tested. Three commonly used hyperelastic models (Neo-Hookean, Mooney-Rivlin and Yeoh models) were used to characterize the mechanical properties of PVC gels, and only the Yeoh model was found to be better for the characterization of the mechanical properties of PVC gels. In addition, we used the Prony series to successfully characterize the viscoelasticity of PVC gels. Then, the fully flexible PVC gel actuator (FFPGA) with long-time static and dynamic response characteristics was studied. It was found that the FFPGA has strong viscoelasticity when working. Finally, we proposed to simplify the FFPGA into a capacitor and designed a high-pass filter in the driving circuit. The self-sensing function of the FFPGA was achieved by superimposing a high-frequency low-voltage sensing signal on the low-frequency high-voltage driving signal as the input signal.

Surfactant-assisted fabrication of room-temperature self-healable dielectric elastomer toward actuation application

Dielectric elastomers are widely used for actuation applications in emerging domains such as tunable optics, tactile displays and soft robotics. However, dielectric elastomer actuators (DEAs) are prone to suffering from electrical or mechanical damage under the conditions of high operating voltage and mechanical stress, leading to a short service time and a low reliability. To address these issues, we in this work made an attempt to facilely develop a self-healable dielectric elastomer that combines high stretchability, dielectric properties, large actuation and effective repairing of mechanical and electrical failure by constructing multitype noncovalent interactions under surfactant assistance. It is demonstrated that the as-prepared elastomer possesses good healability at room temperature. After mechanical injury, a gentle pressure can initiate the recovery of damaged region, and the elastomer film could be subjected to a huge strain of 750% after healing for 24 h. In particular, this as-fabricated DEA that suffered from accidental or repetitive breakdown could still be re-actuated stably without significantly decreasing its actuated strain after quick healing (∼5 min). It is also found that embedding a fluoroelastomer with a fluorosurfactant can achieve larger deformation (tan α = 0.57 at 30 MV/m) due to the improved electromechanical properties. Our strategy for achieving self-healing feature and high actuation performance is favorable for extending lifetime, strengthening damage tolerance and lowering excitation voltages required for the DEAs.

A Healable Resistive Heater as a Stimuli-Providing System in Self-Healing Soft Robots

Self-healing polymers can address the damage susceptibility in soft robotics. However, in most cases, their healing requires a heat stimulus, provided by an external device. This letter presents a self-healing soft actuator with an integrated healable flexible heater, functioning as the stimuli-providing system. The actuator is constructed out of thermoreversible elastomers that are crosslinked by the Diels-Alder (DA) reaction, which provides the healing ability. The heater is manufactured from a DA-based composite network filled with 20 wt% carbon black to provide electrically conductive properties for resistive Joule heating. The flexibility of the heater does not compromise the actuator performance upon integration and the self-healing properties of both heater and actuator allow for damage repair. This includes very large damages, as both heater and actuator can recover (near 100%) from being cut completely in two pieces, using Joule heating at 90°C with a bias voltage of about 30 V. The embedded heater avoids the need for external intervention in the healing process, and provides healing quality assessment and a healing on-demand mechanism, paving the way for an optimum healing solution of damage resilient soft robots that require heat as a healing stimulus.

Kinestatic Modeling of a Spatial Screw-Driven Continuum Robot

Continuum robots offer many advantages for use in miniature diagnostic and interventional surgical devices. However, the creation of snake-like devices with extremely high slenderness ratios, those with great length and small diameter, remains challenging from a device design perspective. To facilitate improved slenderness ratios, high total accumulated bending angles, and high stiffness and mechanical stability of the active section, we propose the use of a flexible screw-driven mechanism to generate large distal actuation forces while still locating motors and other bulky system components at the base of the device. In comparison to tendon-based designs and push-pull rods, the design avoids the capstan-like buildup of friction. In this work, we present design, fabrication, kinestatic modeling, and experimental validation for a two-degree-of freedom, screw-based, multi-backbone continuum robot. The model that compensates the friction in the system most accurately predicts the behavior of the robot and eliminates most of the hysteresis in the input-output behavior.

Study on the improved electromechanical properties of composited dielectric elastomer by tailoring three-dimensional segregated multi-walled carbon nanotube (MWCNT) network

High permittivity and large actuation strain under low actuation voltage have been the “hotspot” on the development and application of dielectric elastomer actuators (DEAs) for decades. In this work, by coating multi-walled carbon nanotube (MWCNT)/silicon rubber (SR) composite on the surface of nickel foam, after which the nickel foam was etched, the segregated MWCNT network structure was filled and encapsulated by SR. As a result, an isolated three-dimensional (3D) MWCNT network was successfully introduced into the SR elastomer matrix. Studies showed that owing to the large amount of accumulated charge on the large polarization interface between MWCNT and SR, high dielectric constant value as high as 10.39 at 1 kHz under 0.8 wt % MWCNT can be endowed to the composited elastomer. In addition, because discontinuity of adjacent MWCNTs in the 3D MWCNT network, the dielectric loss and elastic modulus of the composited elastomer has been significantly lowered, providing a high actuated strain of about 11.61% at a low electric field of 10.1 V·μm−1 under a filler content of 0.6 wt % to the composites. This finding raises a long-range prospect to readily and reliably prepare high-performance polymer based dielectric materials, and the 3D-MWCNT/SR composite elastomer seizes a great potential to be applicated as high-performance DEAs.

Modelling and mechanical design of a flexible tube-guided SMA actuator

Shape memory alloy (SMA) wires are excellent candidates for wearable actuators since they are thin, low weight and have a high actuation force. The main drawbacks are that the wire should be kept straight and needs to be relatively long to enable a large enough actuation stroke. Embedding the SMA wire in a flexible tube largely enhances its applicability since then the counter forces are transferred by the tube material and the tube can be rolled up or attached to flexible surfaces or clothing layers. The performance of such tube-guided SMA actuators is, however, more complicated since it not only depends on the SMA behaviour but also on the tube materials and the actuator construction.In this research, a simple end-state model for a tube-guided SMA actuator system is proposed. We measure and model both the SMA and tube material properties, including tube creep effects, and derive an approximate prediction for the actuator stroke. Validation experiments showed that the predicted stroke during the second heating and cooling experiments agreed well with the measurements and that the average deviation is 9.6%, even though the deviation is much larger (27.3%) for the maximum applied force.

Fabrication and actuation characterisation of a new UV curing acrylic dielectric elastomer

Most commonly used dielectric elastomers (DEs) such as acrylic dielectric elastomers VHBTM 4910 need a high actuation voltage and pre-stretching to obtain a large actuation strain, and present high mechanical loss caused by viscoelasticity. In this work, we fabricated a new acrylic elastomer by UV curing based on CN9021 and lauryl acrylate. By manipulating crosslinker content, crosslink density changed and physical entanglements of the new material can be affected. Therefore, mechanical properties such as Young's Modulus and mechanical loss of the new material can be controlled, and little change of its glass transition temperature was induced. Results of the actuation test show that the new DE is capable of 9.0% actuation area strain under 11 kV/mm and a good performance under oscillating voltage with different waveforms and frequencies.

An ultrahigh fatigue resistant liquid crystal elastomer-based material enabled by liquid metal

The low crosslink density characteristic of liquid crystal elastomer (LCE) materials causes poor fatigue resistance performance, which has seriously plagued their prospects in industrial applications. Here we report that the introduction of 5 wt% liquid metal nanodroplets (average diameter: ca. 195 nm) into the LCE network can dramatically reinforce the corresponding composite’s mechanical properties, in particular ultrahigh fatigue resistance, capable of bearing unprecedented 10,000 tensile cycles within a large range of strain amplitude up to 70% and 2000 times of continuous actuating deformations. Furthermore, this liquid metal-incorporated LCE composite material exhibits large actuation stroke (maximum actuation strain: 55%), high actuation stress (blocking stress: 1.13 MPa), fully reversible thermal/photo-actuation functions, and self-healing ability at moderate temperatures, which qualifies the composite material for high-load actuators.