Showing papers on "Bimorph published in 1996"

Thin film shape memory alloy microactuators

Abstract: Thin film shape memory alloys (SMAs) have the potential to become a primary actuating mechanism for mechanical devices with dimensions in the micron-to-millimeter range requiring large forces over long displacements. The work output per volume of thin film SMA microactuators exceeds that of other microactuation mechanisms such as electrostatic, magnetic, thermal bimorph, piezoelectric, and thermopneumatic, and it is possible to achieve cycling frequencies on the order of 100 Hz due to the rapid heat transfer rates associated with thin film devices. In this paper, a quantitative comparison of several microactuation schemes is made, techniques for depositing and characterizing Ni-Ti-based shape memory films are evaluated, and micromachining and design issues for SMA microactuators are discussed. The substrate curvature method is used to investigate the thermo-mechanical properties of Ni-Ti-Cu SMA films, revealing recoverable stresses up to 510 MPa, transformation temperatures above 32/spl deg/C, and hysteresis widths between 5 and 13/spl deg/C. Fatigue data shows that for small strains, applied loads up to 350 MPa can be sustained for thousands of cycles. Two micromachined shape memory-actuated devices-a microgripper and microvalve-also are presented.

Ink=jet print head with piezo-electric actuator

Abstract: The ink-jet print head 1 has a nozzle plate 2 with an orifice 5 that connects with an ink containing chamber 4 . The underside of the chamber is formed by a laminated actuator element 3 that is electrically excited and causes pressure to be applied to the fluid. The top surface is in the form of a flexible diaphragm and the lower elements 6 are of glass or silicon. Between these elements is a piezo-electric bimorph construction 7 that when energised causes a deflection to occur and so produces the ink-jet action.

Analysis of piezoelastic structures with laminated piezoelectric triangle shell elements

Abstract: In the recent development of active structural systems and microelectromechanical systems, piezoelectrics are widely used as sensors and actuators. Because of the limitations of theoretical and experimental models in design applications, finite element development and analysis are proposed and presented in this paper. A new laminated quadratic C° piezoelastic triangular shell finite element is developed using the layerwise constant shear angle theory. Element and system equations are also derived. The developed piezoelastic triangular shell element is used to model 1) a piezoelectric bimorph pointer and 2) a semicircular ring shell. Finite element (triangular shell finite element) solutions are compared closely with the theoretical, experimental, and finite element (thin solid finite element) results in the bimorph pointer case. Natural frequencies and distributed control effects of the ring shell with piezoelectric actuators of various length are also studied. Finite element analyses suggested that the inherent piezoelectric effect has little effect on natural frequencies of the ring shell. Vibration control effect increases as the actuator length increases, and it starts leveling off at the seven-patch (70%) actuator. Coupling and control spillover of lower natural modes are also observed.

Semipassive bimorph flexible mirrors for atmospheric adaptive optics applications

Abstract: A semipassive bimorph mirror is considered as the most promising corrector for low-order and at the same time low-cost atmo- spheric adaptive optical systems. Theoretical and experimental results of the response functions study are presented. A simple response function histeresis compensation method is suggested. The efficiency of correct- ing the first eight Zernike polynomials with a 17-electrode bimorph mirror is given. It is shown that such a corrector can be successfully used to compensate turbulence with the Kolmogorov spectrum. © 1996 Society of Photo-Optical Instrumentation Engineers.

Snapping microswitches with adjustable acceleration threshold

Abstract: This paper presents the design, fabrication and testing of prestressed bimorph microbeams for applications to tunable acceleration switches. The prestressed bimorph beams are buckled due to the residual stress difference between two dissimilar films, thereby generating initial beam deflections upon fabrication. Necessary and sufficient conditions for snapping action of the deflected bimorph beam have been derived from snap-through buckling analysis. A set of SiO 2 /p + -silicon bimorph beams has been designed and fabricated in three different lengths, 800, 900 and 1000 μm. The electrostatic snap-through voltage for each microbeam has been measured as 32, 56.3 and 76.5 V, respectively. Micromechanical properties of beam materials have been measured from on-chip test structures. It is demonstrated that the three different microswitches with a 7 μg proof-mass can be applicable to acceleration switches, where threshold acceleration levels can be adjustable within the ranges 0–14, 0–35 and 0–47 g , respectively, under inter-electrode bias voltages of 0–76 V.

Curved piezoactuator model for active vibration control of cylindrical shells

Abstract: A composite differential equation of motion for a bimorph configured thin curved uniformly polarized piezoactuator pair surface bonded to a cylindrical shell is derived and the approximate analytical expressions for the equivalent forces exerted by the actuator on a cylindrical shell are obtained The in-phase configuration is studied The piezoactuators exertx and θ line forces and a uniform pressure load over the patch for in-phase configuration The in-phase forces show a saturation behavior with increase in thickness

Advances in the development of an intelligent helicopter rotor employing smart trailing-edge flaps

Abstract: Significant advances in the development of a Froude scaled helicopter rotor model featuring a trailing-edge flap driven by piezoceramic bimorph actuators for active vibration suppression are discussed. A quasisteady aerodynamic analysis used to determine flap size and actuator requirements is presented. The block force and stroke of the current actuators are evaluated using two theories and compared with experimental results. The dynamic performance of the actuator as well as the actuator - flap assembly is examined. Earlier hover tests showed severe degradation in flap deflections with increasing rotor speed, and flap deflections were too small to be effectively utilized for significant vibration control. To investigate the causes of the performance degradation, new blades are constructed and tested in vacuo to isolate the effects of centrifugal loading on the actuator - flap system. A beam model of the piezo bimorph including propeller moment effects is formulated to better illustrate the physical mechanisms affecting the system in a rotating environment. The cause of the reduced deflections is traced to frictional forces created at the junction where the flap is supported during rotation of the blades. The use of a thrust bearing was found to alleviate this problem and subsequent hover tests showed a dramatic increase in flap deflection at high excitation frequencies.

Missile flight control using active flexspar actuators

Abstract: A new type of subsonic missile flight control surface using piezoelectric flexspar actuators is presented. The flexspar design uses an aerodynamic shell which is pivoted at the quarter-chord about a graphite main spar. The shell is pitched up and down by a piezoelectric bender element which is rigidly attached to a base mount and allowed to rotate freely at the tip. The element curvature, shell pitch deflection and torsional stiffness are modeled using laminated plate theory. A one-third scale TOW 2B missile model was used as a demonstration platform. A static wing of the missile was replaced with an active flexspar wing. The 1 in 2.7 in active flight control surface was powered by a bimorph bender with 5 mil PZT-5H sheets. Bench and wind tunnel testing showed good correlation between theory and experiment and static pitch deflections in excess of . A natural frequency of 78.5 rad with a break frequency of 157 rad was measured. Wind tunnel tests revealed no flutter or divergence tendencies. Maximum changes in lift coefficient were measured at which indicates that terminal and initial missile load factors may be increased by approximately 3.1 and 12.6 g respectively, leading to a greatly reduced turn radius of only 2400 ft.

Soft-handling gripper driven by piezoceramic bimorph strips

Abstract: This paper is a study on the hybrid position/force control of a two-fingered miniature gripper driven by piezoelectric bimoph cells. The system is composed of the flexible cantilevers and a compact force sensor attached to the tip of one finger. Control action is applied by two piezoelectric bimorph strips placed at the base of each finger. The theoretical model of the electro-mechanical system is developed and applied to the study of a control problem where the gripper is commanded to grasp its object with a time-constant force 0.01 N at a prescribed commanded fingertip position. The PID control algorithm is introduced to drive the gripper.The system control behaviour is examined both theoretically and experimentally.

Cw industrial rod YAG:Nd 3+ laser with an intracavity active bimorph mirror

Abstract: A special type of resonator with an intracavity wide-aperture active mirror was built, and a concave spherical bimorph active corrector was investigated. An increase of laser beam quality by a factor of 2–2.5 was achieved in a multimode regime of laser generation with an intracavity-controlled mirror. It was shown that various radiation mode structures could be formed at the laser output and in the far-field zone.

Improvements to atomic force microscopy cantilevers for increased stability

Abstract: A modification of commercially manufactured atomic force microscopy cantilevers which reduces the bending of the V‐shaped legs due to changes in temperature is described. Gold‐coated silicon nitride cantilevers are a bimorph system in which the different thermal expansion coefficients of the materials comprising the system can produce a temperature‐dependent change in curvature. Other stress‐related effects might also be responsible for the observed bending. By removing the gold film and redepositing gold only at the end of the V‐shaped legs, a reduction in the bending of the cantilever is accomplished while the required optical reflectivity for the laser deflection system is retained. Imaging x‐ray photoelectron spectroscopy, scanning electron microscopy, and changes in the detector photodiode signal related to bending of the cantilever are shown for modified and unmodified tips.

Micro contact pin structure with a piezoelectric element and probe card using the same

Abstract: A micro contact structure and a probe card to be used in testing performance of a semiconductor integrated circuit device formed on a semiconductor wafer have improved contact characteristics The contact structure includes a micro contact pin having electric conductivity formed on one end of a beam which is movable in a vertical direction, and a piezoelectric element formed on the beam to drive the beam in the vertical direction The beam is made of silicon on the surface of which is formed of a conductive thin film, and the micro contact pin has a pyramid shape The piezoelectric element is a bimorph plate mounted on an upper surface of the beam or both upper and lower surfaces of the beam

Process and apparatus for detecting the limit level of liquids and bulk materials

Abstract: In a process for the detection of the limit level of liquids and bulk materials in containers and pipelines, the change in the oscillation behavior of a sensor which is excited to oscillation is detected electronically and used to trigger a switch command. As sensor there is used a parallel bimorph piezoelectric element (22) having a common central electrode (44) and two outer electrodes (46, 48). A first alternating voltage (U1) with an oscillator frequency (f1) is applied between the central electrode (44) and a first outer electrode (46), a second alternating voltage is measured as amplitude of oscillation (U2) with corresponding oscillation frequency (f2) between the central electrode (44) and the second outer electrode (48), and the measured amplitude of oscillation (U2) or oscillation frequency (f2) is converted into an output switch signal. In a device suitable for the carrying out of the process, the piezoelectric element (22) is inserted in liquid-tight manner into a plastic cover (24), the plastic cover (24) in its turn being fastened in liquid-tight manner to a plastic housing which passes through the wall (16) of a container or a pipeline, and the plastic cover (24) together with the piezoelectric element (22) extends into a protective tube (18) developed on the plastic housing (12).

Acceleration sensor and shock detecting device using the same

Abstract: A small accelaration sensor which is highly sensitive over a large frequency region and which varies little in characteristics such as sensitivity. A piezoelectric element is formed by connecting two main faces of retangular LiNbO 3 piezoelectric substrates, in which the polarization axes are directed oppositely. Supporters comprising LiNbO 3 directly connected to one end of the piezoelectric element. Eletrodes of chromium-gold being 0.2 μm are thick are successively connected to the two main faces of the piozoelectric element and to the supporters, thus to produce a cantilever structure bimorph electromechanical transducer.

Caterpillar‐type piezoelectric d33 bimorph transducer

Abstract: A piezoelectric bimorph transducer utilizing piezoelectric d33 coefficient was developed. This bimorph consists of piezoelectric segments bonded by a polymeric agent and was fabricated by a dicing and layering technique. The transducer has superior piezoelectric characteristics compared to standard piezoelectric d31 bimorphs. Piezoelectric coefficients, electrical admittance, mechanical compliance, and losses of the actuator were found to increase with increasing driving electric field.

Scanning tunneling microscopy head having integrated capacitive sensors for calibration of scanner displacements

Abstract: Scanning tunneling microscopy heads having some tip–displacement measurement capability are essential for quantitative and accurate measurements A scanning tunneling microscopy head based on a bimorph parallelogram scanner with a metallized glass cube situated above the tunneling tip is described The cube acts as a counterelectrode or as a mirror for capacitance‐based and interferometric measurements of scanner displacements The capacitive sensors are mounted on differential screws facing the cube in such a way that the lateral Abbe error in the measurement of actual tip–displacements is minimized The sensor electronics uses a Howland‐type alternating current source, and has a deviation from linearity of less than 015% up to 30 μm and a low frequency bandwidth of 1 kHz

A low power, tight seal, polyimide electrostatic microvalve

Abstract: An electrostatically-actuated polyimide microvalve is developed with sub-micron gaps between the electrodes to provide high force with low power consumption (< 1 mW) Built-in residual stress results in a curled bimorph cantilever which allows for a n-Licroactuator with large displacement This microactuator is used to open and close a fluid path hole etched in silicon for a microvalve The microactuator can be actuated with 25V for a displacement of 200 {mu}m The cantilever actuator is mainly composed of polyimide, which is flexible enough to conform over the flow hole, thereby eliminating the need for the design of a valve seat

Image shifting mechanism and imaging device

Abstract: The disclose is intended to miniaturize the actuator of an image shifting mechanism, to operate the actuator at high speed, and to reduce the effect of image shifting on image resolution. In an image shifting mechanism, a pair of bimorph type piezoelectric elements are disposed on both sides of a refraction plate. The bimorph type piezoelectric elements have a cantilever structure. The base end sides of the bimorph type piezoelectric elements are bonded and secured to a stage, and the free end sides are sandwiched between an upper holding plate and a lower holding plate so as to support one end of the refraction plate. When the bimorph type piezoelectric elements are displaced, the refraction plate can be inclined around its rotation center O. In the case of this structure, the specifications of the refraction plate and the bimorph type piezoelectric elements are determined so that the relationship between the moment of inertia Ic around the rotation center of the moving portions of the image shifting mechanism and the moment of inertia Ig around the center of gravity of the image shifting mechanism is Ic/Ig≦1.6.

Bimorph adaptive optics: elements, technology, and design principles

Abstract: The present paper is concerned with existing deformable bimorph mirrors, their advantages and disadvantages; an effective technology of their construction is proposed providing a significant increase of the mirrors sensitivity as well as their controllable aperture. In accordance with the technology described industrial one-channel bimorph mirrors have been developed and investigated intended for use in laser optics and as well as a 3.3-meter bimorph mirror for optical telescope. Results of the investigation strongly confirm the effectiveness of the proposed technology for improvement of characteristics of controllable bimorph mirrors which represent a perfect instrument for `small' adaptive optics being of great importance for laser techniques and astronomic telescopes even today.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Mosaic adaptive bimorph mirror

Abstract: The invention pertains to the field of adaptive optics and can be used for the static and dynamic guidance of a wave front in a variety of optical devices and systems including astronomical telescopes, industrial laser systems and optical guidance and tracking systems. In the proposed mosaic adaptive bimorph mirror, multilayered local bimorph structures in the form of piezo-electric elements are used to deform the reflecting surface. The piezo-electric elements in question each comprise at least two piezo-ceramic plates (4) fixed on the bottom of a housing (1) the interior cavity of which is filled with an elastic sealant (9).

Governing equations of piezoelectric plates with graded properties across the thickness

Abstract: Two-dimensional governing equations for electroded piezoelectric plates with graded material properties across the thickness are derived from the three-dimensional equations of linear piezoelectricity by extending Mindlin's power series expansion to the mechanical displacement, electric potential and the thickness-graded properties, i.e., the elastic stiffnesses, piezoelectric coefficients, dielectric permittivity, and mass density. The couplings of the extensional and flexural motions due to the graded material properties, in addition to those due to the anisotropy of material properties, are clearly disclosed in these newly derived equations which reduce to Mindlin's equations of homogeneous nonpiezoelectric plates when the graded material properties contain only the zeroth-order terms in the power series expansion. Dispersion curves for both the homogeneous piezoelectric plates and piezoelectric bimorphs are calculated from the 3-D equations and from the present 2-D first-order equations, and the comparison shows that the agreement is very close for frequencies up to and including the fundamental thickness-shear frequencies. An electrode-plated piezoelectric ceramic cantilever plate with thickness-graded piezoelectric coefficients is studied in detail. Resonance frequencies, modes of vibrations and static responses are computed and discussed.

R&D program on bimorph mirrors at the ESRF

Abstract: The very low emittance of new synchrotron sources and the increasing number of micro-focusing applications make the production of highly stable and well defined beams increasingly necessary. The use of flexible mirrors whose curvature can be changed while maintaining a correct figure appeared to be a very attractive solution. For over two years, the ESRF has been developing a new approach which consists of making an X-ray mirror from an active material such as piezoelectric ceramics. With respect to conventional bender this concept, already used in astronomical and laser applications, has the advantages to be mechanics free, very compact and relatively cost effective. This paper presents the status of the ESRF's developments in this field. First, theoretical and technical descriptions of the system are given. Experimental tests of various configurations confirmed the potential of this concept. For example, two 150 mm long bimorph mirrors set into a Kirkpatrick-Baez geometry gave a focused spot of 10 micrometers (vertical) X 20 micrometers (horizontal). Finally, the developments of in-situ control systems (strain gauges, optical devices), necessary to fully exploit the capabilities of these active optics, are discussed.

Optimization of bimorph based double amplifier actuator under quasistatic situation

Abstract: Bimorph based double amplifier actuator is a new type of piezoelectric actuation structure which combines both bending and flextensional amplification concepts. As a result the displacement of the actuator can be more than ten times larger than the tip displacement and can be used in air acoustic transducers as an actuation element. This paper studied the dependence of displacement on actuator parameters and optimum design issues for the cover plate (the flextensional part of the actuator) theoretically and experimentally.

Development of a polymeric piezoelectric C-block actuator using hybrid optimization technique

Abstract: A new class of polymeric piezoelectric bimorph actuators, called C-blocks because of their curved shape, has been developed to overcome limitations of conventional bimorph and stack piezoelectric configurations. Design tradeoffs are investigated in the current research using various performance criteria such as maximum deflection, force, and strain energy. The set of design variables to optimize the C-block actuators, which can be used alone or can be combined in series and/or parallel, includes both continuous and discrete parameters. Therefore, a hybrid optimization technique is developed to address the nonlinear mixed continuous/discrete optimization problem. The results of the optimization procedure indicate useful trends toward microscale actuator development for the most efficient implementation of these actuators.

Deflection-voltage performance of asymmetrically activated piezoelectric C-block actuators

Abstract: As the field of smart materials and structures emerges, there is an increasing need for high- force, high-displacement actuators. An actuator architecture that shows potential in meeting this need is the C-block. C-blocks are curved piezoelectric laminated beams, poled in the radial direction, that flex when voltage is applied. One of the main advantages of C-blocks is they can be combined into distributed arrays to generate more force and/or deflection. The original C-block design was a polymeric bimorph and required the piezoelectric layers to experience both tension and compression. Unfortunately, ceramic versions of the actuator would fail as a result of the tensile stress. Therefore, the C-block design has been modified to an asymmetrically loaded unimorph. This paper introduces a ceramic C-block actuator design along with a simple model for deflection-voltage performance. To verify the model, piezoelectric polymeric and ceramic C-block prototypes were fabricated and deflection-voltage experiments were performed. These experiments demonstrate that the model predicts well the performance of asymmetric C-blocks. The model may be used to design a variety of C-block actuators, potentially including a high-force, high displacement actuator for smart structures applications.

Shock sensors using direct bonding of LiNbO/sub 3/ crystals

Abstract: We have developed a shock sensor made with a bimorph type cantilever using by a technique of directly bonding piezoelectric single crystals. The cantilever's polarization-inverted structure was achieved by directly bonding LiNbO/sub 3/ single-crystal wafers having reverse polarization. This technique did not require any bonding agent. The basic characteristics of the shock sensor were evaluated. The resonance frequency of the cantilever having a length of 2 mm was 20 kHz. The sensor made from 140/spl deg/ rotated Y cut LiNbO/sub 3/ wafers had a high sensitivity of 6.4 mV/G, and excellent linearity.

The role of piezoceramic microactuation for advanced mobility

Abstract: This paper presents the potential role of piezoceramic microactuation in micro-robotics for future space missions, e.g. unmanned sample-return missions to Mars, in search of life or evidence of prebiotic materials. The focus of the paper is on the advanced mobility with the desired characteristics of high force, displacement, and operability over a wide temperature range, at the cost of lowest possible mass, volume, and power. A comparison of the various actuation technologies including piezoceramic, shape memory alloys, polymeric actuators and magnetostrictive materials is presented. The comparison suggests piezoceramics to be the most promising candidate. The concept of a flexible microactuator based on tailored films of lead lanthanum zirconate titanate, PLZT, deposited on flexible substrates is described. Such flexible microactuators are expected to offer a multifold enhancement in the force and displacement capabilities over those of the current state-of-the-art actuators based on bulk ceramic materials. Of special interest is the promise of high efficiency actuation from an optimized thin film based flexible bimorph structure by contact-less optical activation.

Force Control of a Flexible Finger with Distributed Sensors and Piezoelectric Actuators

Abstract: This paper is concerned with the theoretical and experimental study of the force control of a miniature robotic finger that grasps an object at portions other than the fingertip. The artificial finger is a uniform flexible cantilever equipped with a distributed set of compact grasping force sensors. Control action is applied by a piezoceramic bimorph strip place at the base of the finger. The mathematical model of the assembled electromechanical system is developed. The distributed sensors are described by a set of concentrated mass-spring systems. The formulated equations of motion are applied to the study of control problem where the finger is commanded to grasp its object with a time-constant force 0.03 N regardless of the contact position of the finger with the object. Both the PID and H0, regulators are tested and their control behaviours are compared with each other.

Piezoelectric air transducer for active noise control

Abstract: A new type of piezoelectric air transducer has been developed for active noise control and other air acoustics applications The transducer is based on the composite panel structure of a bimorph-based double amplifier, that is, two parallel bimorphs or bimorph arrays with a curved cover plate as an active face attached to the top of the bimorphs The electro- mechanical and electro-acoustic properties of the double amplifier structure and the transducer are investigated in this paper The displacement of the cover plate of the double amplifier structure can reach millimeter scale with a relatively low driving voltage, which is more than ten times larger than the tip displacement of bimorphs The sound pressure level (SPL) of the transducer can be larger than 90 dB (near field) in the frequency range from 50 to 1000 Hz and be larger than 80 dB (far field) from 200 Hz to 1000 Hz, with the largest value more than 130 dB (near field) Because of its light weight and panel structure, it has the potential to be used in active noise control

Tactile microgripper for application in microrobotics

Abstract: As part of a microrobot we present a micromachined gripper system which has both force sensor and actuator integrated. This gripper is used for handling and assembling and allows control of the gap of the gripper and the gripping force continuously. We use a thermal bimorph actuator for the operation of the gripper. For the force sensor we utilize the piezoresistive effect, known to be very strong in silicon. As compared to previous realizations we have optimized the design: the proposed folded bimorph beam delivers a multiple of the actuators stroke as compared to a simple beam structure. This folded bimorph beam design can also be applied to other bimorph actuators (e.g. piezoelectric, SMA). The actuators maximum stroke is 800 micrometers at a finger length of 1600 micrometers and the maximum force generated is in the order of 1 mN. That means an improvement of a factor of five with respect to designs published earlier. The sensitivity of the sensor finger is about 100 mV/VmN which is an improvement by a factor of three and its shows a good linearity.