Electrostrictive Actuators Research Articles

Transient Electro-Mechanics of Piezoelectric Actuator-Driven Active Mechanical Systems

This paper presents a theoretical model to determine the transient electro-mechanical response of active structures driven by piezoelectric (PZT) actuators. The solution is expressed in terms of actuator and structural mechanical impedances, which are the steady state frequency domain dynamic properties and can be characterized theoretically or experimentally. Theoretical case studies have also been presented using a simple example of a PZT actuator-driven one-degree-of-freedom spring-mass-damper system. The solution of the transient response includes the transient electrical current passing through the PZT actuator and the mechanical response of the system (displacement and force). The solution technique may also be applied to active structures driven by other types of induced strain actuators, including electrostrictive and magnetostrictive actuators.

An Impedance Method for Dynamic Analysis of Active Material Systems

This paper describes a new approach to analyzing the dynamic response of active material systems with integrated induced strain actuators, including piezoelectric, electrostrictive, and magnetostrictive actuators. This approach, referred to as the impedance method, has many advantages compared with the conventional static approach and the dynamic finite element approach, such as pin force models and consistent beam and plate models. The impedance approach is presented and described using a simple example, a PZT actuator-driven one-degree-of-freedom spring-massdamper system, to demonstrate its ability to capture the physics of adaptive material systems, which is the impedance match between various active components and host-structures, and its utility and importance by means of an experimental example and a numerical case study. The conventional static and dynamic finite element approaches are briefly summarized. The impedance methodology is then discussed in comparison with the static approach. The basic elements of the impedance method, i.e., the structural impedance corresponding to actuator loading and the dynamic output characteristics of PZT actuators, are addressed. The advantages of using the impedance approach over conventional approaches are discussed using a simple numerical example. A comparison of the impedance method with the static and the dynamic finite element approaches are provided at the conclusion of this paper.

Polyurethane elastomer actuator

Polyurethane elastomer (PUE) prepared from a polyester glycol, paraphenylenediisocyanate (PPDI), and a mixture of 1,2-propanediol and 1,1,1-tris(hydroxymethyl) propane (TMP) as a chain extender, were found to be actuated by the electric field. The characteristics of the PUE electrostrictive actuator were studied as functions of molecular structure, electrode material, its thickness, dielectric constant and applied field. The PUE actuator was confirmed to move smoothly like a finger.

PMN-PT ceramics for active vibration control

Abstract A 1-D experimental vibration control set-up is studied. It uses a Berlin court piezometer as a vibrating source and the internal piezoelectric calibration ceramic as a sensor. A piezoelectric or electrostrictive actuator made of PMN-PT ceramics (65/35 or 90/10) is mechanically coupled to the sensor and used to con trol the motion at different points of the structure which provides two main reso nance modes between 100 and 1000 Hz. It is shown that the amplitude of motion at resonance can be either enhanced or reduced with the piezoelectric actuator de pending on the phase shift between sensor and actuator, while it can only be en hanced with the electrostrictive actuator. A simple model of the system is pro posed.

Performance of a Smart Vibration Isolator for Precision Spacecraft Instruments

This paper describes the configuration and measured performance of an hybrid, active-passive vibration isolation mount designed to mitigate vibratory disturbances on sensitive spacecraft instruments. The device, called the Active Vibration Canceler (AVC), consists of a passive isolation stage using composite leaf springs faced with shape-memory metal sheet material to provide load-adaptive damping, and an active, force-canceling stage using a motion-amplified electrostrictive stack actuator to augment attenuation of transmitted vibrations in the 10-120 Hz band. The paper discusses the features of the AVC design and active control architecture, and presents results of experiments characterizing the broadband performance of the device. Performance measurements show that the AVC provides up to 40 dB attenuation of base disturbances at 100 Hz, and that the electrostrictive active stage provides in excess of 10 dB attenuation over the passive isolator in the range 10-100 Hz. The measurements indicate that hybrid devices of this type can be effective in reducing transmitted vibrations to sensitive instruments, and that the incorporation of active elements can significantly enhance attenuation of broadband vibrations in isolation applications.

Energy-Based Comparison of Solid-State Induced-Strain Actuators

A study of published literature and information from piezoelectric, electrostrictive, and magnetostrictive actuator vendors has been undertaken to establish the mechanical and electrical operating characteristics of the actuators, and to compare them using output energy density criteria. Output energy values of up to 0.666 J can be achieved with off-the-shelf actuators. Energy density per unit volume was found in the range 1.816-7.280 J/dm3. Energy density per unit mass was found in the range 0.233-0.900 J/kg. In one isolated case, higher energy densities of 11.9 J/dm3 and 1.09 J/kg were identified for a small co-fired PMN stack of 0.00481 J total energy. Energy transformation efficiency between input electric energy and output mechanical energy was found to be: 17-27% for adhesively-bonded PZT and PMN stacks, 5-20% for co-fired PZT and PMN stacks, and 67.1% for TERFENOL-D devices. The overall performance of induced-strain actuators based on output energy density criteria was found to vary widely from vendor to vendor, and even from one model to another within the same vendor catalogue list. These variations are attributed to progress being made currently in both the active material technology and in the detailed mechanical construction of induced-strain actuators based on these materials.

Torsional actuation with extension-torsion composite coupling and a magnetostrictive actuator

This paper presents an analytical-experimental study of using magnetostrictive actuators in conjunction with an extension-torsion coupled composite tube to actuate a rotor blade trailing-edge flap to actively control helicopter vibration. Thin-walled beam analysis based on Vlasov theory was used to predict the induced twist and extension in a composite tube with magnetostrictive actuation. To validate the analysis, extension-torsion coupled Kevlar®-epoxy tubes or different ply lay-ups were fabricated using an autoclave molding technique. They tubes were first tested under static mechanical loads, and tip twist and axial extension were measured by means or a laser optical system and strain gages, respectively. Good correlation between theory and experiment was achieved. Subsequently, these composite tubes were tested under magnetostrictive actuation. The [11] 2 Kevlar-epoxy tube system generated the maximum twist, 0.19 deg in tension and 0.20 deg in compression. The Kevlar-epoxy systems showed good correlation between measured and predicted twist values. Finally, alternate actuator concepts for these tubes, specifically piezoelectric stacks and electrostrictive actuators, were examined, and a piezoelectric stack actuator was round to induce much larger force and twist (approximately 3 times that created by the magnetostrictive actuator/tube system)

Redundant actuators to achieve minimal vibration trajectory tracking of flexible multibodies: Theory and application

We address the problem of inverse dynamics for flexible multibodies, which arises, in trajectory tracking control of flexible multibodies such as space manipulators and articulated flexible structures. Previous research has resolved this trajectory tracking problem by computing the system inputs for feedforward control of actuators at the joints. Recently, the use of distributed actuators like electro-strictive actuators in flexible structures has introduced a new dimension to this trajectory tracking problem. In this paper we optimally utilize such actuators to aid joint actuators for tracking control, and introduce a new inverse dynamics scheme for simultaneously (1) tracking a prescribed trajectory and (2) minimizing ensuing elastic deflections. We apply this scheme for trajectory tracking of a two-link two-joint planar manipulator with joint motors and distributed electro-strictive actuators. Experimental results are presented to contrast our new scheme with other existing methods.

Reliability Studies on Electrostrictive Actuators

Multilayer electrostrictive actuators have numerous applications. Frequently these applications involve harsh mechanical and electrical loads. Furthermore, it is typically expected that these loads be incurred for > 108 repetitions (ideally for an infinite number of cycles). This paper describes the electrical and electro-mechanical analyses used at AVX Corporation to assess the performance characteristics of multilayer ceramic actuators, and addresses the effects of electro mechanical cycling on selected device properties. In this study, lead magnesium niobate based multilayer electrostrictive actuators were subjected to a.c. fields at rated device voltage. Capacitance, dissipation factor, displacement vs. voltage, displace ment hysteresis, electro-mechanical quality factor, and resonant frequency were monitored as a function of electro-mechanical cycling. The actuators exhibited highly stable displacements through out the investigation. Changes observed in other properties indicate a possibility of using them as NDE techniques to assess the actuator reliability.

Dielecetric aging of relaxor ferroelectrics in the Pb (Mg1/3Nb2/3) O3-PbTiO3-Pb (Mn1/3Nb2/3) O3system

Abstract Lead magnesium niobate, Pb (Mg1/3Nb2/3) O3, with, perovskite structure is promising for various applications such as electrostrictive actuators, multilayer capacities and pyroelectric bolometers. For these applications, dielectric aging must be minimal. Aging properties in the Pb (Mg1/3Nb2/3) O3–PbTiO3–Pb(Mn1/3Nb2/3)O3 system have been studied with respect to the chemical composition, microstructure and cation arrangement in B–site in perovskite structure. It is found that they are strongly dependent on the amount of Pb (Mn1/3Nb2/3) O3.

Effect of PZT and PMN actuator hysteresis and creep on nanoindentation measurements using force microscopy

Nanoindentation measurements performed using the atomic force microscope (AFM) are significantly affected, both with regard to indentation curve shape and quantitative values of the measurements (70% variation in measured modulus), by the well-known effects of hysteresis and creep in the lead zirconate titanate (PZT) piezoceramic actuators used to control the positioning and motion of the mechanical components of the AFM. A capacitance-based displacement calibrator has been built and it was discovered that the response of PZT ceramics may vary (up to 66%) depending upon the conditions under which the piezoceramic is calibrated. By replacing the PZT actuators with lead magnesium niobate (PMN) electrostrictive actuators, nanoindentation measurements have been obtained using the AFM that are both reproducible and quantitative.

Dynamics of a deformable mirror actuator

The electromechanical equations governing the motion of the surface of a deformable mirror, due to the activation of a piezoelectric or electrostrictive actuator mechanically located between the mirror surface and the mirror substrate, are derived in terms of the fundamental electromechanical parameters of the mirror-actuator configuration. The equations of motion are solved in the frequency domain and the solutions show reasonable agreement with experimental data such as Bode plots, which characterize the frequency dependence of the amplitude and phase of the mirror surface motion, and with frequency-dependent impedance measurements. Time-domain solutions are used to construct time histories of an actuator under a step-voltage input.

Saw filter resonant frequency adjustment by electro-strictive and piezoelectric actuators

Abstract Abstract: Electrostrictive and piezoelectric actuators are used to adjust the SAW resonant structures by means of of strain induced voltage controlled change of the linear dimensions of the resonators. The effect is also used for the precise measurements of the actuator displacement under the external load with the accuracy 10−5.

On the Use of Electrostrictive Actuators in Recovering the Optical Performance of the Hubble Space Telescope

AbstractThis paper describes the development of a space qualified active mirror—the Articulating Fold Mirror—which forms part of the scheme for recovering the optical performance of the Hubble Space Telescope. Three Articulating Fold Mirrors are incorporated into the optical train of the Jet Propulsion Laboratory's Wide Field and Planetary Camera-2, which was installed into Hubble by astronauts in December, 1993. Each Articulating Fold Mirror utilizes six electrostrictive ceramic multilayer actuators to precisely position a mirror in tip and tilt in order to correct the spherical aberration of the Hubble Space Telescope's primary mirror. Flight qualification aspects of the electrostrictive actuators are described. Pre- and postrepair images from the Wide Field and Planetary Camera, showing the effect of the optical correction, are presented.

An Impedance Method for Dynamic Analysis of Active Material Systems

This paper describes a new approach to analyzing the dynamic response of active material systems with integrated induced strain actuators, including piezoelectric, electrostrictive, and magnetostrictive actuators. This approach, referred to as the impedance method, has many advantages compared with the conventional static approach and the dynamic finite element approach, such as pin force models and consistent beam and plate models. The impedance approach is presented and described using a simple example, a PZT actuator-driven one-degree-of-freedom spring-mass-damper system, to demonstrate its ability to capture the physics of adaptive material systems, which is the impedance match between various active components and host-structures, and its utility and importance by means of an experimental example and a numerical case study. The conventional static and dynamic finite element approaches are briefly summarized. The impedance methodology is then discussed in comparison with the static approach. The basic elements of the impedance method, i.e., the structural impedance corresponding to actuator loading and the dynamic output characteristics of PZT actuators, are addressed. The advantages of using the impedance approach over conventional approaches are discussed using a simple numerical example. A comparison of the impedance method with the static and the dynamic finite element approaches are provided at the conclusion of this paper.

Stresses Near the End of an Internal Electrode in Multilayer Electrostrictive Ceramic Actuators

AbstractStresses near the end of an internal electrode in a multilayer electrostrictive ceramic actuator are studied in detail. A finite element program capable of overcoming two major difficulties is developed. The program solves both the mechanical and electrical coupling problem and the nonlinear electric field and electric displacement relationship for these materials. Results indicate that the stress difference between the coupled and the uncoupled cases can only be distinguished when a stress singularity is present. Tensile stresses are found both in front, and behind, the end of an internal electrode. The magnitude of the stresses is predetermined by the material constants.

Ba/sr Doped Electrostrictive Compositions for Actuator Design

AbstractSolid solutions of lead zirconate titanate (PZT) and lead magnesium niobate (PMN) doped with barium/strontium were developed for use in miniature electrostrictive actuators. The microstructural features of the materials were determined by high-resolution transmission electron microscopy (HREM) and by x-ray diffractometry. The response and the strain hysteresis were measured by applying a sinusoidal or a rectangular voltage pulse. Pulses of variable amplitude and width were applied to the elements to study the switching behavior of 90° domain walls in the materials and to elucidate the initial zero-position “walk off” mechanism. The strain hysteresis or remanent strain of PZT decreased with increasing PMN concentration. A barium-doped PZT (Ba-PZT) composition containing 4 mole% of PMN exhibited ferroelectric relator behavior with a field-induced strain much larger than those of lead magnesium niobate (PMN) electrostrictive materials and a small remanent strain hysteresis.

Enhanced Structural Control with Discretely Attached Induced Strain Actuators

A new configuration where induced strain actuators such as piezoelectric ceramic patches or shape memory alloys are attached to a structure at discrete points (as opposed to being bonded) is presented. This paper specifically addresses discretely attached induced strain actuators like piezoceramic and electrostrictive actuators which are available in the form of plates or patches, and includes actuator flexural stiffness considerations. When activated, such actuators deform along with the structure (like bonded actuators), but in this case the actuator and the structure are free to deform independently. In such a scenario, the in-plane force of the actuator results in an additional moment on the structure and enhanced structural control. Also because now the actuator can be offset from the structure without an increase in the basic flexural stiffness of the structure, the actuator offset distance can be optimized to maximize actuator authority. Enhanced control is demonstrated by comparing the static response of a discretely attached actuator/beam system with its bonded counterpart system. Through a proper choice of the offset distance, the flexural control authority measured in terms of the moment applied to the substrate structure can be increased considerably for stiff and thick substrates. The advantage of this configuration over the bonded configuration is also verified experimentally. The limitations and considerations for the implementation of the concept in realistic structures are also discussed.

Enhancing induced strain actuator authority through discrete attachment to structural elements

In structural control, induced strain actuators are used by bonding them or embedding them in a structure. With bonded or embedded actuators used for inducing flexure, the developed in-plane force contributes indirectly through a locally generated moment. Control authority in this configuration is thus limited by actuator offset distance. In this paper, a new concept of flexural or shape control is presented, whereby induced strain actuators such as piezoelectric ceramic patches or shape memory alloys are attached to a structure at discrete points (as opposed to being bonded). This paper specifically addresses discretely attached induced strain actuators like piezoceramic and electrostrictive actuators which are available in the form of plates or patches, and includes actuator flexural stiffness considerations. This configuration is different from the bonded actuator configuration in two ways. One, because the actuator and the structure are free to deform independently, the in-plane force of the actuator can result in an additional moment on the structure and enhanced control. Second, the actuator can be offset from the structure without an increase in the flexural stiffness of the basic structure. This allows for the optimization of the offset distance to maximize control. Enhanced control is demonstrated by comparing the static response of a discretely attached actuator beam system with its bonded counterpart system. The advantage of this configuration over the bonded configuration is also verified experimentally.

Ceramic Actuators: Principles and Applications

Piezoelectric and electrostrictive actuators, capable of moving something electromechanically, are forming a new field between electronic and structural ceramics. Application fields are classified into three categories: positioners, motors, and vibration suppressors. The manufacturing precision of optical instruments such as lasers and cameras, and the positioning accuracy for fabricating semiconductor chips, which must be adjusted using solidstate actuators, is of the order of 0.1 μm. Regarding conventional electromagnetic motors, tiny motors smaller than 1 cm3 are often required in office or factory automation equipment and are rather difficult to produce with sufficient energy efficiency. Ultrasonic motors whose efficiency is insensitive to size are superior in the minimotor area. Vibration suppression in space structures and military vehicles using piezoelectric actuators is also a promising technology.New solid-state displacement transducers controlled by temperature (shape memory alloy) or magnetic field (amorphous magnetostrictive alloy) have been proposed, but are generally inferior to the piezoelectric/electrostrictive actuators because of technological trends aimed at reduced driving power and miniaturization.