Symmetric Actuator Research Articles

The Vibration Analysis of a Simply Supported Plate Excited by Piezoelectric Actuators

Piezoelectric materials have the advantage of being lightweight, temperature insensitivity low-cost, easy of implementation that can be utilized for passive and active control of structural vibration. They can be surface bonded or embedded in the structures with slight modifications and without significantly changing the structural stiffness of the system. In this investigation, two piezoelectric actuators are symmetrically embedded in a simply supported plate. Electric voltages with the same amplitude and opposite sign are applied to the two symmetric piezoelectric actuators, resulting in the bending effect on the plate. The bending moment is derived and applied to the simply supported plate. The harmonic response of the simply supported plate excited by the piezoelectric actuators is derived and compared with the finite element solution to show the validation of present approach. The effects of the location and exciting frequency of the piezoelectric actuators on the response of the plate are presented through a numerical study.

Validation and modification of the Blade Element Momentum theory based on comparisons with actuator disc simulations

AbstractA comprehensive investigation of the Blade Element Momentum (BEM) model using detailed numerical simulations with an axis symmetric actuator disc (AD) model has been carried out. The present implementation of the BEM model is in a version where exactly the same input in the form of non‐dimensional axial and tangential load coefficients can be used for the BEM model as for the numerical AD model. At a rotor disc loading corresponding to maximum power coefficient, we found close correlation between the AD and BEM model as concerns the integral value of the power coefficient. However, locally along the blade radius, we found considerable deviations with the general tendency, that the BEM model underestimates the power coefficient on the inboard part of the rotor and overestimates the coefficient on the outboard part. A closer investigation of the deviations showed that underestimation of the power coefficient on the inboard part could be ascribed to the pressure variation in the rotating wake not taken into account in the BEM model. We further found that the overestimation of the power coefficient on the outboard part of the rotor is due to the expansion of the flow causing a non‐uniform induction although the loading is uniform. Based on the findings we derived two small engineering sub‐models to be included in the BEM model to account for the physical mechanisms causing the deviations. Finally, the influence of using the corrected BEM model, BEMcor on two rotor designs is presented. Copyright © 2009 John Wiley & Sons, Ltd.

IDENTIFICATION OF THE NONLINEAR FRICTION CHARACTERISTICS IN A HYDRAULIC ACTUATOR USING THE EXTENDED KALMAN FILTER

In this paper, the nonlinear friction characteristic of a custom made symmetrical linear hydraulic actuator is investigated using the Extended Kalman Filter (EKF). A new and very accurate characterization of friction is made by using a quadratic function of the piston velocity. Further to this proposed empirical friction model, the EKF is used to estimate the function coefficients. In this paper, an iterative approach is used to maintain system observability and render the estimation process more reliable. The study is conducted in simulation and by using measured experimental data. The estimated states and parameters by the EKF are found to be convergent to their known values in simulation and, further to experimental results, unique and repeatable. In addition, changes in the friction characteristics, which can occur in the physical system due to wear in the piston seals or degradation in the oil properties, are detected and accurately estimated by the EKF in simulation. This study presents an accurate nonlinear model for the representation of friction in a hydraulic actuator. It paves the way for the implementation of strategies for early fault detection in hydraulic systems.

All-Optical Micromirrors From Nanotube MOMS With Wavelength Selectivity

The photomechanical properties of carbon nano-tubes (CNTs) enable the construction of CNT-based optical actuators. Employing a microelectromechanical systems-compatible nanotube-patterning process by plasma etching, CNT ensembles are integrated into microsystems to realize microoptomechanical systems (MOMS) (CNT-MOMS), where nanotubes behave as both the structural materials and the actuation mechanism. In this paper, following the CNT-MOMS principle, we report on all-optical micromirrors from the CNTs. Photomechanical actuation of single-wall CNTs from polymer-/nanotube-fllm bimorph structures is designed to actuate the micromirrors. A large mirror angular displacement of 19deg is obtained under laser illumination. Bidirectional rotation of the micromirrors is realized by the incorporation of two symmetrical serpentine bimorph actuators with the mirror surface. Furthermore, to add controllability to the micromirror rotations, absorptive-type optical filters are combined with the mirror structure in a suspended filter assembly. With green and red optical filters incorporated in the micromirrors, they show rotational selectivities of 10:1 and 20:1 for the 532-and 658-nm lasers, respectively. Depending on the wavelength of the incoming light, it could be selectively modulated into opposite directions by the micromirror.

The deflection of a simply supported plate induced by piezoelectric actuators

The coupling effects between the mechanical and electric properties of piezoelectric materials have drawn significant attention for their potential applications as sensors and actuators. In this investigation, two piezoelectric actuators are symmetrically embedded in a simply supported plate. Electric voltages with the same amplitude and opposite sign are applied to the two symmetric piezoelectric actuators, resulting in the bending effect on the plate. The bending moment is derived by using the theories of elasticity and piezoelectricity. The analytical solution of the flexural displacement of a simply supported plate subjected to the bending moment is solved by using the plate theory. The analytical solution is compared with the finite element solution to show the validation of present approach. The effects of the size and location of the piezoelectric actuators on the response of a plate are presented through a parametric study.

The static responses and displacement control of circular curved beams with piezoelectricactuators

We analyse the static responses of a circular curved beam bonded with a singlepiezoelectric actuator or symmetric actuators. We also study the characteristics of thecontrol parameters for the displacement control of a cantilever circular curved beamvia piezoelectric actuators in this paper. The uniform circular beam is thin andactuated by thin piezoelectric layers. The piezoelectric unimorph or the bimorphbeam is equivalent to a single-layer structure. The governing equations of thesestructures with small curvature are derived based on one-dimensional beam theory.The static analysis of the segmented beam undergoing radial concentrated loadand concentrated bending moment is given in detail. For a cantilever beam withsingle actuator or symmetric actuators, the theoretical results of the displacementresponses agree well with experimental results reported early and/or the FEM results.The control problem of a cantilever bimorph is studied as the first example. Tocontrol the displacement at the free end by piezoelectric actuation, an explicitexpression of the optimal voltage is obtained for the beam undergoing the radialconcentrated load at an arbitrary location, which indicates the optimal voltage isindependent of the material properties of the middle elastic layer. Numerical resultsshow that the peak control voltage and the negative control voltage will occurwith the changes of the load location and the beam length. The cantilever beamwith symmetric distributed actuators is studied as the second example. As thebeam is loaded by too high a radial concentrated load at the free end, the radialdisplacement of the free end is controlled to the minimum via actuators withgiven input voltage. The optimization of the actuators’ length and location isimplemented. For a given actuator’s length, the optimal actuator’s location is at theclamped end as the central angle of the beam is smaller than a critical value.After the central angle of the beam is larger than the critical value, the optimalvalue of the actuator’s location is dependent on the central angle of the beamand the central angle of the actuators. As the actuator’s location is given, theoptimal length of the actuators is the allowable maximum length of the actuators.

Investigation of an aqueous lithium iodide/triiodide electrolyte for dual-chamber electrochemical actuators

Electrochemical pumping, the electromigration-driven flow of ions and their associated solvent molecules across a permselective membrane, is investigated for the construction of dual-chamber electrochemical actuators. Important features include large volumetric strain, significant pressure generation, and minimal pressure-driven backflow. Aqueous electrolytes have a number of advantages over organic electrolytes such as dimethylformamide; four concentrations of a lithium iodide/triiodide electrolyte are investigated here. Fluid transport decreases as the ionic strength increases, with the waters associated with each cation decreasing from 16 to 6 as [Li +] increases from 0.5 to 3.5 M. As a result, the maximum volumetric strain which might be achieved in a symmetric dual-chamber actuator, about 18%, is for an electrolyte of intermediate concentration, 2 M LiI + 0.5 M I 2. Pressure generation experiments using this electrolyte reached 295 psig (∼20 atm) in 10 min, with about 50% of the available charge consumed. For this pressure, losses measured at open circuit, ca. 13 psi/min, are lower than previously measured losses using a dimethylformamide electrolyte. Simultaneous measurement of pressure generation and fluid transport provides a measure of the pressure-driven backflow, 0.13 μL/min, which compares favorably with those estimated for the porous separators used for electroosmotic-driven flow.

Development of symmetric type slim optical pickup actuator for flexible disk system

Recently, in information storage devices, several characteristics such as high data transfer rate, large storage capacity and small drive size are required as high-definition television (HDTV) broadcasting, mobile devices, and notebook personal computer (PC) were popularized. In optical disk drive (ODD), several actuators have been developed to satisfy these specifications. In this paper, we presented the symmetric type slim actuator with efficient tracking magnetic circuits for the flexible disk system. At first, electromagnetic (EM) circuits were designed to have big driving force for high sensitivities through design of experiments (DOE). And, in structural parts, we designed the actuator that had proper control bandwidth through several redesigns of moving parts. Consequently, the final model was fabricated and dynamic tests were experimented. And, it was checked that our actuator had a very high tracking sensitivity and could be applied to the flexible disk system.

Electric field simulation of a symmetrical plasma actuator system

In this paper, the electric field of a symmetrical actuator system is simulated and the plasma flow control mechanism is analysed. The peristaltic acceleration process in electromagnetic field is simulated with finite-difference time_domain method and the result accurately consists with theoretical analysis, and the peristaltic acceleration mechanism is discussed. Our results may provide a theoretical basis for improving the peristaltic acceleration and optimizing the symmetrical plasma actuator configuration.

PARAMETER IDENTIFICATION IN A HIGH PERFORMANCE HYDROSTATIC ACTUATION SYSTEM USING THE UNSCENTED KALMAN FILTER

This paper describes an early fault detection strategy for a high performance hydrostatic actuation system, referred to as the ElectroHydraulic actuator (EHA). Safety is crucial for the EHA which is being applied in flight surface actuation systems and in robotics. The proposed fault detection methodology in this manuscript uses a new state/parameter estimation algorithm, referred to as the Unscented Kalman Filter (UKF) to estimate parameters which cannot be measured using sensors. The parameters reflect the health condition of the system and changes in their normal values can be related to the inception and progression of faults in the system. The two parameters of interest in this study are the viscous damping coefficient of a symmetrical actuator and the effective bulk modulus of the hydrostatic system. The feasibility of the approach is demonstrated by a simulation study and using experimental data. Changes in the viscous damping coefficient provide valuable information about the lubricating propertie...

평행 평판 정전형 구동기를 이용한 가변 광 감쇠기

The micromachined variable optical attenuator(VOA) was presented in the paper. The VOA has two single mode fiber(SMF) aligned with free space and symmetric parallel plate actuator with microshutter, which can control a amount of light by driving the actuator. In the paper, analysis on driving performances of the VOA was performed and can be reduced threshold voltage through the decreasing displacement actuating range. This paper presents a VOA that is fabricated using bosch deep silicon etching process with silicon on insulator(SOD wafer. The VOA consists of driving electrode, ground electrode, actuating microshutter, and mechanical stopper. In this VOA, actuating shutter is driven by electrostatic force and the threshold voltage is close to 28V, 46V come along with the spring width of 5<TEX>${\mu}{\textrm}{m}$</TEX>, 7<TEX>${\mu}{\textrm}{m}$</TEX> respectively. Attenuation range is measured from 2.4㏈ to 16.7㏈.

Bending actuation in polyurethanes with a symmetrically graded distribution of one-way shape memory alloy wires

Structures are being actuated by embedding shape memory alloy (SMA) wires into compliant materials, such as polyurethane. To achieve bending actuation, these wires are placed in opposing wire configurations, where multiple wires are often employed to enhance the amplitude of the bending actuation response. In this investigation, a procedure has been developed for fabricating polyurethanes with a symmetrically graded distribution of SMA wires. The effects of grading the distribution of one-way SMA wires have been characterized using full-field displacement deformation measurements obtained with the digital image correlation (DIC) technique. These measurements have been used in a one-dimensional (1D) model of bending actuation to determine the “equivalent two-way shape memory effect (SME)” of the graded wire distribution. To utilize the 1D actuation model, the constitutive properties of the polyurethane structure predicted by rule-of-mixture formulations were reduced to account for the differences in strain between the SMA wires and the polyurethane matrix. The graded wire distribution was also found to significantly stiffen the polyurethane structure. The level of equivalent two-way SME therefore became limited by the maximum recovery stress of the SMA wires, with a maximum level that was approximately 75% less than previously measured levels in an opposing wire configuration. However, the bending actuation behavior was more symmetric, and the actuated bending deflections were similar to those observed when using more compliant materials. It was also predicted that the symmetrically graded wire distribution would exhibit a better balance between actuation amplitude and uniformity, which combined with the more symmetric actuation behavior makes the graded wire distribution potentially more desirable for achieving higher actuation frequencies with distributed actuation concepts in new applications, such as miniaturized double diaphragm pumping devices.

Dynamic characteristics of a bitable linear actuator with moving permanent magnet

The dynamic characteristics of an ax symmetrical linear actuator with axially magnetized moving permanent magnet are obtained using combined field and circuit approach. The magnetic field of the actuator has been analyzed using the finite element method over a current-displacement sampling grid. Two field analyses are carried out for each point of the grid - one for the real system and one for the system where the permanent magnet is considered as a soft magnetic body. For each point of the grid, data for the total flux linkage, electromagnetic force and the coil inductance are extracted from the magnetic field analysis. These data are approximated by bicubic spline functions, which are employed in the solution of the system of ordinary differential equations of the electrical circuit and the mechanical motion. Results are obtained for the time variations of the coil current, mover displacement, mover velocity and electromagnetic force. The results for the current and displacement are verified experimentally.

Design of a new high-performance electrohydraulic actuator

This paper describes the design and prototyping of a new high-performance actuation system that combines the benefits of conventional hydraulic systems and direct-drive electrical actuators, namely high torque/mass ratio and modularity. It is referred to as the electrohydraulic actuator (EHA) and results from the fusion of the above-mentioned technologies. The EHA is a unique device with its own characteristics and requires hydraulic components that are specifically tailored to its needs and requirements. Based on a mathematical model of the EHA, the requirements for its components are determined. These requirements are used as a basis for component selection, component modification, and design of a customized new symmetrical linear actuator. The analysis of the EHA presented is supported by experimental data and explains the extremely high level of performance attained by a prototype of the EHA.

Nonlinear control strategy development for asymmetric actuators

We develop a nonlinear control method for asymmetric actuators. Asymmetric actuators do not generate symmetric power during an application. Thrusters and shape memory alloy wires are examples of this class of actuators that produce only unidirectional forces. Hydraulic and pneumatic cylinders are generally asymmetric because, under constant pressure, the generated force in the forward direction is different than that in the reverse direction. Existing control methods assume a symmetric actuation, and therefore, application of asymmetric actuators calls for new control schemes. Current control techniques implement a bias in utilizing asymmetric actuators. However, the amount of the bias depends on the control effort and is not constant. Also, the use of a bias changes the system equilibrium point and introduces a steady-state error. We propose a control scheme capable of producing any biased input. The controller is a second-order system coupled to the system through quadratic terms. The application of quadratic terms for the control input enables us to generate any biased control input, which can be utilized by asymmetric actuators.

DESIGN AND ANALYSIS OF A NEW SYMMETRICAL LINEAR ACTUATOR FOR HYDRAULIC AND PNEUMATIC SYSTEMS

In this paper, the performance of hydraulic actuation systems is analyzed and, it is observed that the performance of symmetrical (rotary) actuators is significantly better than their linear asymmetrical counterpart. The deficiency of linear actuators, resulting from their asymmetry, manifests itself as an undesirable dynamic effect related to the pressure characteristics of the actuator chambers. Subsequently, a new symmetrical design for linear actuators is proposed. In this design, the active areas of the two pressure chambers are made equal without the need for a dead-space on the fixed end of the piston as required by commercial double rod pistons. The paper discusses the benefits of this new design and demonstrates the advantages of its flow characteristics and its command input/force relationship. The theoretical observations are supported by experiments conducted on a large hydraulic robot. The Workmaster, formerly manufactured by Thorn EMI Robotics.

Transient heat transfer behavior of one-dimensional symmetric thermoelectric SMA actuators

The main purpose of this paper is to study the transient heat transfer behavior of one-dimensional symmetric thermoelectric Shape Memory Alloy (SMA) actuators, without assuming a small ratio between the layer thicknesses of SMA and semiconductor. For the transient heat transfer with a constant current density, it is proved that there is an upper bound for the current density so that the temperature distribution along the SMA layer is stable. For the transient cooling problem with a constant current density, it is proved that there is a lower bound for the current density so that the temperature at the interface between SMA and semiconductor layers is always decreasing to its stable state, and it may not be always decreasing if the current density is below the lower bound. Estimates for these bounds are derived. The physical implications of main results are also discussed.

Experimental Control of Flexible Structures Using Nonlinear Modal Coupling: Forced and Free Vibration

This paper is an experimental study of free and forced vibration suppression in a piezoceramic actuated flexible beam via the nonlinear Modal Coupling Control (MCC). The method is based on transferring the oscillatory energy from the plant to an auxiliary second order system (controller), coupled to the plant through nonlinear terms. The proposed controller produces an input that can be utilized by unidirectional actuators. Unidirectional actuators do not generate symmetric power during an application. Shape memory alloys, thrusters and cable based actuators are examples of this class of actuators. Existing control methods assume a symmetric actuation and therefore application of unidirectional actuators call for new control techniques. Current control techniques implement a bias in utilizing unidirectional actuators. However, the amount of the bias is variable and depends on the control effort. Moreover, the use of a bias changes the system equilibrium point and introduces a steady state error. The proposed controller is used to control the first mode of a flexible beam. The results show that the method is more effective than conventional control approaches in conjunction with unidirectional actuators.

Flow over an obstacle emerging from the wall of a channel

Direct simulation of laminar flow over a rising obstacle (an actuator) reveals the presence of vortical structures identical to those found in flow over a stationary obstacle, intensified and stretched by the upward velocity of the boundary. Following deceleration of the actuator to a stationary position, this amplification leads to a vortex shedding event in the wake region as the flow evolves toward its steady state. Three obstacle shapes are analyzed: one is streamwise symmetric, and two are skew symmetric. The symmetric actuator is also raised into a higher Reynolds number flow and in a final test is raised at half-speed into the low Reynolds number flow. Results indicate that the time scale of the transient is independent of Reynolds number, depending primarily upon the rising time of the actuator and to a lesser degree its shape. A CTIVE control in the turbulent boundary layer of a wallbounded flow is an area of research that has significant implications for the air transport industry: substantial reductions in fuel costs may be achieved through small reductions in skin-friction drag; higher operating temperatures (and better efficiency) may be obtained in gas turbines through control of the heat transfer between exhaust gases from the combustor and the turbine blades. Different strategies for control include mass transfer through porous walls1 and so-called smart skins: an actuator on the wall responds to a flow by adjusting its height to steer the wall region dynamics (the bursting processes that are signatures of turbulent'flows and primary sources of momentum and heat transport).2 Critical to the success of active control is not only an understanding of near-wall turbulence (a great deal of research has been directed toward this over the past 30 years) but also an understanding of the phenomena that are to be used to effect control—the transient behavior of flow over a moving obstacle (concerning which little data are available). Flows over three-dimensional, stationary obstacles have been studied in the laboratory, in the physical domain, and through numerical simulation.36 In a comprehensive survey consisting of both experimental and computational tests, Mason and Morton7 have analyzed laminar, steady flows past a variety of stationary obstacles. As an extension of this body of work, focus is redirected toward transients associated with obstacles that emerge in time, utilizing an algorithm that simulates flow in a channel with three-dimensional, time-dependent wall geometries. The code has been verified using wall geometries for which there exist known steady and unsteady solutions8; this includes comparisons with data from Mason and Morton.7 Between these benchmark tests involving simpler flows and the control work involving turbulent flows fall intermediate analyses of transients associated with low and moderate Reynolds number laminar flows over rapidly emerging obstacles. To distinguish between the stationary and the rising obstacle, the latter shall be referred to as an actuator. Three actuator shapes have been selected, one streamwise symmetric and two skew symmetric. All are smooth functions, symmetric in the spanwise (crossflow) direction. As in the cases analyzed by Mason and Morton,7 Reynolds numbers have been chosen that lie below the value at which flow (over a stationary obstacle) becomes unsteady. Using a local Reynolds number (Ret), based on obstacle height and the mean velocity that would exist through the height interval

Asymmetric actuation and sensing of a beam using piezoelectric materials

The purpose of the present work is the modeling of a beam actuated by a ceramic piezoelectric on the top with a PVDF piezoelectric on the opposite side acting as a sensor. The two piezoelectric are different in types, may be of arbitrary length and can be positioned independently along the beam. Since there is only one actuator, the asymmetric excitation induces transverse and axial displacement in the beam. This asymmetric actuation contrast with the symmetric actuation normally considered in the literature. Symmetric actuation implies no axial displacement. Here, both piezos are considered perfectly bonded to the beam and the Bernoulli–Euler hypothesis is used for the displacement field. The variational approach with Hamilton’s principle is put to use in the theoretical model. Hamilton’s principle states that the definite time integral of the Lagrangian shall be stationary. This formulation, which is energy based, allows one to consider any boundary conditions and to take into account the dynamic effects of both piezos on the beam response. The theoretical model gives the axial and transverse displacements, the strains, the mean quadratic velocity of the beam, and the voltage of the PVDF piezo sensor as a function of the voltage given to the actuating ceramic piezo. Experimental results are compared to the theoretical model for the case of the beam with free-ends boundary conditions.