Actuator Layers Research Articles

Integrated control of active steering and braking systems with tyre forces and cornering stiffness estimation

A model-based integrated controller for active steering and active braking systems is proposed to enhance vehicle handling and stability. A hierarchical scheme is adopted, including vehicle layer based on model predictive control (MPC), actuator layer, and observer layer. The MPC controller adopts a predictive model with the lateral force of front axle and yaw moment as inputs, which leaves the nonlinearity and coupling of tyre forces to be solved by the tyre force allocation algorithm in actuator layer, leading to more precise control action. In order to maintain satisfactory control performance with respect to the variation of tyre character, a dual extended Kalman filter (DEKF) is designed in the observer layer to estimate tyre forces and cornering stiffness. The observed results are used to reduce the mismatch of the reference models in vehicle layer and actuator layer. The effectiveness of the proposed controller is demonstrated by simulations in CarSim environment.

Dynamic stability and nonlinear vibration of rotating sandwich cylindrical shell with considering FG core integrated with sensor and actuator

In this research, the dynamic stability and nonlinear vibration behavior of a smart rotating sandwich cylindrical shell is studied. The core of the structure is a functionally graded material (FGM) which is integrated by functionally graded piezoelectric material (FGPM) layers subjected to electric field. The piezoelectric layers at the inner and outer surfaces used as actuator and sensor, respectively. By applying the energy method and Hamilton\'s principle, the governing equations of sandwich cylindrical shell derived based on first-order shear deformation theory (FSDT). The Galerkin method is used to discriminate the motion equations and the equations are converted to the form of the ordinary differential equations in terms of time. The perturbation method is employed to find the relation between nonlinear frequency and the amplitude of vibration. The main objective of this research is to determine the nonlinear frequencies and nonlinear vibration control by using sensor and actuator layers. The effects of geometrical parameters, power law index of core, sensor and actuator layers, angular velocity and scale transformation parameter on nonlinear frequency-amplitude response diagram and dynamic stability of sandwich cylindrical shell are investigated. The results of this research can be used to design and vibration control of rotating systems in various industries such as aircraft, biomechanics and automobile manufacturing.

Vibrations piezo-control of FGM beam in a thermal environment

An analytical method on the active vibration control of a functionally graded beam equipped with layers of piezoelectric sensors and actuators, in a thermal environment, is studied. The study based on Euler-Bernoulli theory and finite element method, applied to a flexible beam divided into a finite number of elements. The equations of motion are obtained by applying the principle of Hamilton. The structure is modeled analytically then numerically and the results of the simulations are presented to visualize the states of their dynamics.

A Feedback Controlled MEMS Probe Scanner for On-chip AFM

Atomic force microscope (AFM) provides a unique possibility in nanoscience research and development for interrogation and manipulation of matter at nanoscale. Miniaturization of AFM significantly reduces the manufacturing cost and breaks the barrier to widespread adoption of this scientific instrument. This paper presents the characterization and control of a novel microelectromechanical system (MEMS)-based AFM. For in-plane motion, the device is equipped with a micro stage with integrated electrostatic actuators and electrothermal sensors. For use in taping-mode AFM imaging, a microcantilever is embedded within the device, featuring a piezoelectric layer for actuation. Positive position feedback (PPF) controller is used to attenuate the highly resonant dynamics of the stage. Scanning performance of device is evaluated by tracking a raster pattern where a 50 Hz triangular signal is applied to the actuators along the X axis. To reduce the tracking error, turnaround points of triangular signal are smoothed by using an optimization method. Moreover, the closed-loop bandwidth is increased with inversion-based feedforward technique. A 50Hz optimal reference signal combined with an inversion-based feedforward technique results in a fivefold decrease in root mean square of tracking error compared with triangular reference signal.

Edge effects in elastic and piezoelectric laminated panels under thermal loading

An analytical solution for accurately predicting the edge effects in elastic and hybrid multilayered panels integrated with piezoelectric actuator and sensor layers under thermal gradient loading is presented. The associated thermal problem is solved independently by performing a heat transfer analysis. The extended Reissner-type mixed variational principle is employed to develop the governing equations of the three dimensional (3D) piezothermoelasticity problem. Their solution is obtained using the mixed-field multiterm extended Kantorovich method, developed recently by the author group. The mixed field solution exactly satisfies all the mechanical and electric boundary conditions pointwise, leading to an accurate solution. The formulation is general, and is applicable for composite, sandwich and hybrid panels with arbitrary lay-up and boundary conditions. The solution is validated against the exact 3D solution available for simply supported panels. The free edge stress field in sandwich and hybrid composite laminates is investigated under uniform as well as gradient thermal loading. The solution successfully captures the singularity in free edge interlaminar stresses. The significance of pyroelectric coupling on the free edge thermal stress field is investigated, and the feasibility of its control through electric field actuation is examined.

Multipoint Bending and Shape Retention of a Pneumatic Bending Actuator by a Variable Stiffness Endoskeleton.

We propose a pneumatic bending actuator integrated with a low-melting-point alloy-based variable stiffness endoskeleton that can bend at multiple points and maintain its bent shape without power supply. Local stiffness of the soft actuator can be altered by melting or hardening the endoskeleton with electric heat applied through embedded metal wires. Bending points of the actuator can be changed by selecting different points of the endoskeleton to be melted, and the bending angle can be controlled by injected air pressure. The shape of the bent actuator is maintained by hardening the alloy even when pressure is reduced to the initial state. We demonstrate that the actuator can be bent differently with only one pneumatic actuation layer by combining multipoint bending and the shape retention function, and thus the actuator can be used for lifting, holding, and unloading an object. We believe that the simple machinery of the actuator will be useful in programming complicated motions of soft robotic fingers, fins, and tentacles.

Actuation and blocking force of stacked nanocarbon polymer actuators

ABSTRACTWe have developed stacked nanocarbon polymer actuators that are composed of several nanocarbon polymer actuator films using nonwoven fabric as insulation layers. The nonwoven fabric prepared through electrospinning methods has extremely-low-density structures, which do not significantly prevent the motions of each nanocarbon actuator layer. Therefore, stacking several thin nanocarbon polymer actuators using nonwoven fabric as insulation layers is expected to increase generated force without decreasing the displacement of a one-layer actuator. We have prepared stacked actuators with one, two, three, four, and seven layers using this method. The displacement and blocking force of these actuators are measured and compared with those of one-layer actuators of different thicknesses. Displacement is weakly dependent on the thickness of the actuator films of the stacked actuators. On the contrary, it decreases considerably as the thickness of the actuator film of the one-layer actuator increases. In both cases, blocking force is proportional to the thickness of actuator films. We have developed a stacked actuator model based on a trilayer actuator model and confirmed the experimental results using the model.

Analysis on nonlinear vibrations near internal resonances of a composite laminated piezoelectric rectangular plate

The nonlinear vibrations and chaotic motions of a simply supported symmetric cross-ply composite laminated piezoelectric rectangular plate subjected to the transverse and in-plane excitations are analyzed in the case of primary parametric resonance and 1:3 internal resonance. It is assumed that different layers of the symmetric cross-ply composite laminated piezoelectric rectangular plate are perfectly bonded to each other and with piezoelectric actuator layers embedded in the plate. Based on the Reddy’s third-order shear deformation plate theory, the nonlinear governing equation of motion for the composite laminated piezoelectric rectangular plate is derived by using the Hamilton’s principle. The Galerkin’s approach is employed to discretize the partial differential governing equation to a two-degree-of-freedom nonlinear system under combined the parametric and external excitations. The method of multiple scales is utilized to obtain the four-dimensional averaged equation. Numerical method is used to find the bifurcation diagram, the periodic and chaotic motions of the composite laminated piezoelectric rectangular plate. The numerical results illustrate the existence of the periodic and chaotic motions in the averaged equation. It is found that the chaotic responses are especially sensitive to the forcing and the parametric excitations. The influences of the transverse, in-plane and piezoelectric excitations on the bifurcations and chaotic behaviors of the composite laminated piezoelectric rectangular plate are investigated numerically.

Active damping of sound transmission through an electrorheological fluid-actuated sandwich cylindrical shell

An exact model is proposed for sound transmission through a sandwich cylindrical shell of infinite extent that includes a tunable electrorheological fluid core, and is obliquely insonified by a plane progressive acoustic wave. The basic formulation utilizes Hamilton’s variational principle, the classical and first order shear deformation shell theories, the Kelvin–Voigt viscoelastic damping model (for the electrorheological fluid-core layer), and the wave equations for internal/external acoustic domains coupled by the proper fluid/structure compatibility relations. The Fourier–Bessel series expansions are used to arrange the governing (coupled) system equations in state-space form. The classical Sliding Mode Control law is then applied to semi-actively reduce sound transmission through the composite cylinder by smart variation of stiffness and damping characteristics of the electrorheological fluid-core actuator layer according to the control command. Numerical results present both the uncontrolled and controlled sound transmission loss spectra of the sandwich cylindrical shell at three angles of incidence for three distinct sets of material input parameters that represent the electric-field dependency of the complex shear modulus of the electrorheological fluid-core layer. The superior soundproof performance of electrorheological fluid-based sliding mode control system in avoiding the highly detrimental sound transmission loss dips occurring throughout the critical resonance and coincidence regions is demonstrated. Likewise, remarkable enhancements in the sound insulation characteristics of the electrorheological fluid-actuated structure utilizing the first or second electrorheological fluid material model are achieved within the stiffness-controlled region, especially at lower frequencies in near-grazing incidence situation. A number of limiting cases are introduced and validity of the formulation is confirmed by comparison with the available data.

Nonlinear finite element modeling of vibration control of plane rod-type structural members with integrated piezoelectric patches

This paper addresses modeling and finite element analysis of the transient large-amplitude vibration response of thin rod-type structures (e.g., plane curved beams, arches, ring shells) and its control by integrated piezoelectric layers. A geometrically nonlinear finite beam element for the analysis of piezolaminated structures is developed that is based on the Bernoulli hypothesis and the assumptions of small strains and finite rotations of the normal. The finite element model can be applied to static, stability, and transient analysis of smart structures consisting of a master structure and integrated piezoelectric actuator layers or patches attached to the upper and lower surfaces. Two problems are studied extensively: (i) FE analyses of a clamped semicircular ring shell that has been used as a benchmark problem for linear vibration control in several recent papers are critically reviewed and extended to account for the effects of structural nonlinearity and (ii) a smart circular arch subjected to a hydrostatic pressure load is investigated statically and dynamically in order to study the shift of bifurcation and limit points, eigenfrequencies, and eigenvectors, as well as vibration control for loading conditions which may lead to dynamic loss of stability.

Evaluating actuator distributions in simply supported truncated thin conical shell with embedded piezoelectric layers

In this investigation, distributed modal actuator forces of simply supported truncated conical shell embedded by a piezoelectric layer are studied. Piezoelectric layer is distributed on the conical shell surface as actuators. Three types of distributions are considered: longitudinal, circumferential, and diagonal distributions. First, electromechanical equations of the conical shell with embedded piezoelectric actuator layer are extracted. Then modal expansion method is used to define independent modal characteristics of the conical shell. For each kind of distribution, three case studies are considered and evaluated. Results showed that in the longitudinal and diagonal distributed actuator, membrane force in the longitudinal direction is the dominant force and in the circumferential distributed actuator, the membrane force in the circumferential direction is the dominant force. The effects of cone angle, piezoelectric thickness, and piezoelectric layer segmentation on modal forces of each distributed actuator are also studied. In circumferential distributed actuator, modal forces increase as the cone angle increases. This phenomenon in the longitudinal and diagonal distributed actuator is almost reversed. The piezoelectric layer segmentation effect on the modal forces distribution is also evaluated, and it showed that this phenomenon has a critical effect on the modal forces distribution.

Smart control and vibration of viscoelastic actuator-multiphase nanocomposite conical shells-sensor considering hygrothermal load based on layerwise theory

Smart control and vibration analysis of laminated sandwich truncated conical shells with piezoelectric layers as sensor and actuator are presented in this paper. The core of the sandwich structure is reinforced by carbon fibers and carbon nanotubes (CNTs) where the effective material properties are obtained by Halpin–Tsai model. The actuator layer is subjected to external voltage and a Proportional-Derivative (PD) controller is used for sensor output control. Based on Kelvin–Voigt model, the structural damping effects are assumed. The formulation of the problem is based on the layerwise first order shear deformation theory (FSDT). Considering the continuity of the displacements and the internal stress fields at the interfaces of the layers, the motion equations are derived utilizing Hamilton's principle. The solution of the problem is carried out by differential quadrature method (DQM) for calculating the frequency of the smart sandwich structure. The effects of different parameters such as structural damping, weight percent of CNTs, boundary conditions, geometrical parameters of the structure, semi vertex angle of the cone, external voltage, temperature and moisture changes are examined on the vibration response of the smart sandwich structure. Numerical results indicate that using a PD controller can increase the frequency of the structure. In addition, the hygrothermal load decreases the vibration frequency of the system.

FBG based shape sensing of a silicone octopus tentacle model for soft robotics

The shape sensing of a soft silicone octopus tentacle model using FBG sensors is presented in this paper. A polyimide thin film layer integrates FBG sensors is embedded into a soft silicone model as the strain limited layer for pneumatic actuation. The relation between the Bragg wavelength shift (BWS) value and the bending curvature of the soft silicone model is measured through the FBG calibration process. The curvature values of the soft silicone model at four bending shapes are calculated based on the BWS values and the interpolation algorithm. The reconstruction of the 3D shapes of the soft silicone model at different bending status are realized using the curve fitting function, and the correctness is verified. The results show that the error between the calculated and actual values of the bending curvature is no more than 2.1%, the proposed FBG-based sensing approach is effective for the measurement of the bending shape of the soft silicone model, it has application prospect in the field of soft robotics.

On the Free Vibrations of Piezoelectric Carbon Nanotube-Reinforced Microbeams: A Multiscale Finite Element Approach

In this article, the vibrational behavior of beam-type microstructures made of carbon nanotube-reinforced composite is studied based on a finite element approach accounting for micro-/nanoscale effects. It is considered that the surface of microbeams is perfectly bonded with a piezoelectric actuator layer. First, the random distribution of CNTs into the polymer matrix is modeled using a three-phase representative volume element (RVE), and the properties of CNT-reinforced polymer are determined for various volume fractions of CNT. In the selected RVE, the interphase region formed due to the interaction between CNTs and the matrix is taken into account. In the next step, natural frequencies of composite piezoelectric microbeams subject to different end conditions are calculated. The influences of CNT volume fraction, interphase, boundary conditions and geometrical properties on the results are investigated.

Integrated optimization of actuators and structural topology of piezoelectric composite structures for static shape control

This paper investigates a new integrated optimization method for laminated composite structures with piezoelectric patch actuators. Three kinds of design variables, i.e. the actuators’ locations, electrical voltages applied on piezoelectric patches and host structural pseudo-densities, are simultaneously optimized to improve the overall deformation precision. To freely place piezoelectric actuator on the host structure surface regardless of coincident finite element in classic lamination theory (CLT), the multi-point constraints (MPC) method is used here to simulate the perfect bonding between actuator layer and host layer, which inherits the advantages of avoidance of remeshing process analytical sensitivity as well as efficient lamination description during the movement of actuators in optimization iterations. For applying to spatially complex shape control, a modified shape error function based on the relative error between computed and desired surfaces is used. The finite circle method (FCM) is implemented to prevent the overlaps among the actuators and those between actuators and boundaries of the global design domain. Finally, numerical examples with plane or curved host structure are tested and discussed to demonstrate the validity and efficiency of this method.

Piezoelectric Membrane Actuators for Micropump Applications Using PVDF-TrFE

This paper presents the design, fabrication, and performance evaluation of a biocompatible piezoelectric membrane actuator (PMA) using polyvinylidene fluoridetrifluoroethylene (PVDF-TrFE). Electrode structure optimization was verified by a finite element method simulation software. Fabrication was done utilizing only standard microfabrication techniques. 1-μm-thick membrane and 1.5-μm-thick actuator layers were formed by spin coating using PVDF-TrFE. The surface roughness of the fabricated film was measured as 7.9 nm using a tabletop atomic force microscope (AFM) and remnant polarization at 200 V was measured as 5.38 μC/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . Deflection measurements were performed with an Al coated tipless AFM probe using a precision nano displacement system, which consists of a ferroelectric tester, a table top AFM, and a computer. A 432 nm displacement was obtained at 9 V under non-resonant conditions from a PMA with 2250 μm diameter. Since all moving structures were fabricated from a polymer material, high displacements could be obtained without fracture. The results demonstrated that the proposed PMA can be a good candidate for membrane type micropumps, especially to be used in biomedical applications, where low driving voltage and biocompatibility are required.

Nonlinear thermal torsional post-buckling of carbon nanotube-reinforced composite cylindrical shell with piezoelectric actuator layers surrounded by elastic medium

The paper focuses on thermal torsional post buckling of functionally graded carbon nanotube reinforced composite cylindrical shells with sur-bonding piezoelectric layers and embedded in an elastic medium. The distribution of reinforcements through the thickness of the shells is considered to be uniform and functionally graded. The basic equations using geometrically nonlinearity in von Karman-Donnell sense within the classical thin shell theory are established. The torsional post-buckling behavior of the piezoelectric functionally graded carbon nanotubes reinforced composite (FG-CNTRC) shells is analyzed with using the Airy's stress function and the Galerkin's method, in which a three-term approximate solution of the deflection of the shell is assumed. Effects of thermal environment, CNT volume fraction, piezoelectric layers (the thickness and the constant voltage), distribution type of the reinforcement, dimensional parameters and Winkler and Pasternak foundation are investigated in this paper. Numerical and graphical results show that the carbon nanotube volume fraction and the piezoelectric layers as well as the elastic foundation and the thermal loads have significantly influenced on the torsional postbuckling behavior of nanocomposite shells.

Infrared actuation-induced simultaneous reconfiguration of surface color and morphology for soft robotics

Cephalopods, such as cuttlefish, demonstrate remarkable adaptability to the coloration and texture of their surroundings by modulating their skin color and surface morphology simultaneously, for the purpose of adaptive camouflage and signal communication. Inspired by this unique feature of cuttlefish skins, we present a general approach to remote-controlled, smart films that undergo simultaneous changes of surface color and morphology upon infrared (IR) actuation. The smart film has a reconfigurable laminated structure that comprises an IR-responsive nanocomposite actuator layer and a mechanochromic elastomeric photonic crystal layer. Upon global or localized IR irradiation, the actuator layer exhibits fast, large, and reversible strain in the irradiated region, which causes a synergistically coupled change in the shape of the laminated film and color of the mechanochromic elastomeric photonic crystal layer in the same region. Bending and twisting deformations can be created under IR irradiation, through modulating the strain direction in the actuator layer of the laminated film. Furthermore, the laminated film has been used in a remote-controlled inchworm walker that can directly couple a color-changing skin with the robotic movements. Such remote-controlled, smart films may open up new application possibilities in soft robotics and wearable devices.

Optimization of dynamic buckling for sandwich nanocomposite plates with sensor and actuator layer based on sinusoidal-visco-piezoelasticity theories using Grey Wolf algorithm

Optimization of embedded piezoelectric sandwich nanocomposite plates for dynamic buckling analysis is presented in this work based on Grey Wolf algorithm. The Grey Wolf algorithm mimics the leadership hierarchy and hunting mechanism of grey wolves in nature. In addition, the main steps of hunting, searching for prey, encircling prey, and attacking prey are employed. The structure is composed of a laminated functionally graded-carbon nanotubes reinforced layers as core integrated with sensor and actuator layers considering structural damping effects. Two-dimensional magnetic and 3D electric fields are applied to core and piezoelectric layers, respectively. Sinusoidal shear deformation theory is utilized for obtaining the motion equations and differential quadrature method is applied for solution. Also, a proportional–derivative controller is employed to control the dynamic behavior of the structure. Finally, the optimum designs for the structure are evaluated using proposed Grey Wolf algorithm based on the geometrical parameters of plate, applied voltage, controller parameters, volume fraction of carbon nanotubes, spring, and shear constants of foundation. Numerical results indicate that by applying the positive voltage and transverse magnetic field the optimum dimensionless frequency of the system decreases.

Vibration analysis and control of delaminated and/or damaged composite plate structures using finite element analysis

The present article deals with the vibration analysis of delaminated and/or damages composite plate structures. Delamination and/or debonding occur in the laminate due to various load and extreme environmental conditions in their service time. A Matlab based finite element model is developed for centrally located delamination. The Active Fiber Composite actuator layer is placed at top or bottom of the laminated plate. A small delamination in the mid-plane is considered. Numerical results are generated for different boundary conditions and delamination sizes. The formulation of the governing equation is based on minimum potential energy approach. The key observation is that natural frequencies decrease due to delamination because of a decrease in stiffness of the structures. Certain local mode shapes can also be observed in the delamination region. The stiffness of the delaminated composite plate can be enhanced by applying voltage to the active fibre actuator layer.