Bimorph Bender Research Articles

2D+1 degree of freedom equivalent circuit model for LiNbO3/metal/LiNbO3 bimorph bending cantilever

2D+1 degree of freedom equivalent circuit model for LiNbO3/metal/LiNbO3 bimorph bending cantilever

Dielectric Elastomer Actuator Driven Soft Robotic Structures With Bioinspired Skeletal and Muscular Reinforcement.

Natural motion types found in skeletal and muscular systems of vertebrate animals inspire researchers to transfer this ability into engineered motion, which is highly desired in robotic systems. Dielectric elastomer actuators (DEAs) have shown promising capabilities as artificial muscles for driving such structures, as they are soft, lightweight, and can generate large strokes. For maximum performance, dielectric elastomer membranes need to be sufficiently pre-stretched. This fact is challenging, because it is difficult to integrate pre-stretched membranes into entirely soft systems, since the stored strain energy can significantly deform soft elements. Here, we present a soft robotic structure, possessing a bioinspired skeleton integrated into a soft body element, driven by an antagonistic pair of DEA artificial muscles, that enable the robot bending. In its equilibrium state, the setup maintains optimum isotropic pre-stretch. The robot itself has a length of 60 mm and is based on a flexible silicone body, possessing embedded transverse 3D printed struts. These rigid bone-like elements lead to an anisotropic bending stiffness, which only allows bending in one plane while maintaining the DEA's necessary pre-stretch in the other planes. The bones, therefore, define the degrees of freedom and stabilize the system. The DEAs are manufactured by aerosol deposition of a carbon-silicone-composite ink onto a stretchable membrane that is heat cured. Afterwards, the actuators are bonded to the top and bottom of the silicone body. The robotic structure shows large and defined bimorph bending curvature and operates in static as well as dynamic motion. Our experiments describe the influence of membrane pre-stretch and varied stiffness of the silicone body on the static and dynamic bending displacement, resonance frequencies and blocking forces. We also present an analytical model based on the Classical Laminate Theory for the identification of the main influencing parameters. Due to the simple design and processing, our new concept of a bioinspired DEA based robotic structure, with skeletal and muscular reinforcement, offers a wide range of robotic application.

Bistable Threshold Humidity Sensor Switch with Rectangular Bimorph Bending Plate.

Energy-autonomous bistable threshold sensor switches have the potential to reduce costs because they do not need any electrical energy supply for monitoring physical quantities, such as relative humidity. In previous work, a bistable beam-like sensor switch with switching hysteresis was manufactured from sheet metal and a partially coated water vapor-sensitive hydrogel (poly(vinyl alcohol)/poly(acryl acid)). Based on the beam theory, a corresponding mechanical model was developed. However, bending plates should be used instead of bending beams to separate the humidity to be measured from the electrical contacts. For this reason, this work deals with the development and realization of a mechanical model based on the plate theory to describe the deflection of a silicon bimorph bending plate partially coated with hydrogel that swells with increasing humidity. For implementing a switching hysteresis a plasma-enhanced chemical vapor deposition silicon dioxide (SiO2) layer is used, which was deposited and structured on top of the silicon plate. The hydrogel layer itself is patterned on the surface of the bending plate using a stamp technique. To validate the mechanical model, the switching hysteresis of the miniaturized sensor switch was measured optically by a camera measurement device.

Vibration Tracking Control of Piezoelectric Bimorph Bender in Novel Reciprocal State Space Form

In this paper, the deflection of a piezoelectric bimorph bender is controlled to track given time varying reference command solely utilizing direct acceleration measurement without integration. Novel estimator that directly applies acceleration measurement and controller that applies estimated state derivative signals have been developed in reciprocal state space (RSS) form. Simulations for the augmented system of both closed loop system and estimator have been carried out to successfully verify the proposed methods. The design approach in this paper is applicable to smart structures with accelerometers as sensors.

Design of thermo-piezoelectric microstructured bending actuators via multi-field asymptotic homogenization

The use of integrated MicroElectroMechanical systems (MEMS) is recently spread thanks to their improved sensitivity, accuracy and reliability. Accurate preliminary computations born from the need of high precision in the manufacturing process of such devices. Piezoelectric materials are broadly employed in this field as direct converters between mechanical and electrical signals and some of these piezoelectric materials show pyroelectric features, which involve thermo-electrical interactions. Pyroelectric bending actuators are analyzed in the present study in plane conditions. They consists of active PZT layers with in-plane polarization and a microstructured composite layer characterized by a periodic microstructure where PZT fibers with an out of plane polarization are immersed in a polymeric matrix. The constitutive law of the composite layer at the mesoscale has been determined by means of a multi-field asymptotic homogenization technique, recently developed for thermo-piezoelectric materials. Overall constitutive equations characterizing the behavior of the microstructured layer at the mesoscale have been derived and the closed form of the overall constitutive tensors has been provided for the equivalent first-order (Cauchy) homogenized continuum. Deflection of unimorph and bimorph bender actuators has been investigated in relation to their geometrical features, exploiting the out of plane piezoelectric properties of the composite layer, which modify the stiffness of the entire bender. An accurate description of benders behavior at the structural length scale is of fundamental importance in order to design devices with high performances. In this regard, the influence of the microstructure on the global response of the actuator is investigated in the present study in order to understand how the composite material can be tailored to meet specific design requirements.

Miniature Resonant Ambulatory Robot

This article describes the design, manufacture, and performance of a prototype miniature resonant ambulatory robot that uses piezoelectric actuators to achieve locomotion. Each leg is comprised of two piezoelectric bimorph benders, joined at the tip by a flexure and end effector. Combinations of amplitude and phase can be used to produce a wide range of motions including swinging and lifting. A lumped mass model previously developed is described as a design tool to tune the resonance modes of the end effector. The completed robot was driven with frequencies up to 500 Hz resulting in a maximum forward velocity of approximately 520 mm/s at 350 Hz. A frequency analysis was also performed to determine the effects of ground contact on the performance of the robot. This analysis showed a significant reduction in the resonance gain and frequency.

A comparison between direct measurements and inference results from an acoustic propagation experiment in Currituck Sound

An acoustic propagation experiment was conducted in Currituck Sound to characterize low frequency propagation in a very shallow-water environment with water depths of only a few meters. Signals from a Combustive Sound Source (CSS) were recorded on bottom mounted geophones and a vertical array of hydrophones. The CSS produces a broadband signal with significant low frequency energy, and the analysis presented in this paper focuses on frequencies below 2.5 kHz. A statistical inference method was applied to obtain an estimate of the sediment sound-speed profile as a function of depth in the seabed. During the experiment, in situ measurements of compressional and shear wave speed and attenuation were also collected 30 cm below the sediment-water interface. Bimorph bender elements were employed to generate and receive horizontally polarized shear waves in the frequency range from 200 Hz to 1 kHz. Compressional waves were measured using cylindrically shaped piezoelectric elements operated in the 5 kHz to 100 kH...

Design and optimisation of an aerofoil with active continuous trailing-edge flap

ABSTRACTThis paper presents the design and optimisation of an aerofoil with active continuous trailing-edge flap (CTEF) investigated as a potential rotorcraft active control device. Several structural cross-section models are developed: high-fidelity NASA STRucture ANalysis (NASTRAN) and University of Michigan/Variational Asymptotic Beam Section Code (UM/VABS) models and a reduced-order analysis model. The validation of the reduced-order model is established by comparing its predictions of CTEF deformations with those of NASTRAN and UM/VABS analyses, which both show good agreement. The 2D aerodynamic characteristics of the CTEF aerofoil are evaluated using XFOIL and Computational Fluid Dynamics (CFD) analyses: FUN3D and Overset Transonic Unsteady Rotor Navier-Stokes (OVERTURNS). XFOIL, coupled with the reduced-order structure model, is adopted for optimisation study. The accuracy of XFOIL in predicting the aerodynamic pressure of the CTEF aerofoil is verified using CFD simulations, which shows sufficient fidelity. The predicted variations of aerodynamic coefficients with a CTEF angle are compared among the aerodynamic analyses. The optimisation process is developed and applied to two bimorph bender configurations: a Macro-Fibre Composite (MFC) solid bender and an MFC stack bender. The solid bender is used to confirm the functioning of the optimisation procedure and to use its optimal layout as a reference to the stack design, the primary design object. A linear tapered shape is found to be the optimum for a MFC solid bender, which generates an average of 63% more CTEF angles than those of an optimal rectangular bender. An optimised MFC stack bender is shown to resemble the shape of the solid bender. A four-ply bimorph is considered the best choice among the stack layouts because of its large output of CTEF angles and relatively less plies required. The CTEF angle produced by the four-ply optimal layout ranges from 7.6° to 5.3° with speeds from 0 to 200m/s at an angle of attack (AoA) of 6°. The reduction in the CTEF angle with AoA is less steep than that with speed, ranging from 6.5° to 5.8° with AoA from 0 to 8° at speed of 166m/s. An average of 14% increase in CTEF angles is achieved through optimisation for the four-ply bimorph.

Vibration-based piezoelectric micropower generator for power plant wireless monitoring application

This paper investigates the factors affecting the performance of a vibration based micropower generator for a power plant wireless monitoring application. A bimorph bender, one of micropower generator methods, was used in this work. The ANSYS program was used to study the distribution of stress–strain in each model design, and MATLAB was used to simulate and investigate the extracted power. Triangular, rectangular and trapezoidal cantilevers were chosen to analyse the effect of the bender shape on the power produced. The tests were conducted using the same input excitation conditions (10m/s2), frequency range of (50–150Hz). The effect of the configuration arrangement (horizontal and vertical) of the PZT bimorph cantilever on the power generation (poling series) was also investigated. The simulation result showed that the maximum stress–strain value was produced in the triangular bender shape with equal distribution on all the surface areas. The measurements’ results showed that the triangular cantilever produced maximum power compared to other bender shapes for both horizontal and vertical directions and single test. The horizontal and vertical arrangements of the cantilevers showed that the vertical arrangement could produce more power than the horizontal arrangement. The experimental results showed concurrence with theoretical models.

Design of a Charge Drive for Reducing Hysteresis in a Piezoelectric Bimorph Actuator

This paper describes the design of a charge drive for reducing the hysteresis exhibited by a piezoelectric bimorph bender. Existing charge drive circuits cannot be directly applied to bimorph benders since they share a common electrode. In this paper, a new charge drive circuit and electrical configuration are implemented that allows commonly available piezoelectric bimorphs to be linearized. This circuit consists of four major components, including, a high voltage amplifier, a differential amplifier, a piezoelectric load, and a PI feedback controller. An isolation amplifier was used to achieve a differential amplifier with a high common-mode rejection ratio. The charge drive was tested by driving a series poled three layer bimorph bender. The experiment showed a significant improvement to the hysteresis of the bender when compared to a typical voltage drive. This paper has identified an alternative Feedback method to improve the ac hysteresis performance of a piezoelectric bender by using a charge drive.

Investigation of piezoelectric bimorph bender transducers to generate and receive shear waves

This paper further demonstrates the ability of piezoceramic bimorph bender elements to preferentially generate and receive near-surface shear waves for in situ sediment characterization measurements, in terrestrial as well as marine clay soils. The bimorph elements are housed in probe transducers that can manually be inserted into the sediment and are based on the work of Shirley [J. Acoust. Soc. Am. 63(5), 1643–1645 (1978)] and of Richardson et al. [Geo.—Marine Letts. 196–203 (1997)]. The transducers can discretely generate and receive horizontally polarized shear waves, within their bimorph directivity patterns. The use of multiple probes allows one to measure the shear wave velocity and attenuation parameters in the sediment of interest. Measured shear wave data on a hard clay terrestrial soil, as well as on soft marine sediments, are presented. These parameters along with density and compressional wave velocity define the elastic moduli (Poisson’s ratio, shear modulus, and bulk modulus) of the sediment, which are of interest in various areas of geophysics, underwater acoustics, and geotechnical engineering. Discussion will focus on use of the probes in both terrestrial and marine sediment environments. [Work supported by ARL:UT Austin.]

Design, fabrication and characterization of a piezoelectrically actuated bidirectional polymer micropump

We present the design, fabrication and characterization of a new, piezoelectrically actuated fully polymeric three chamber peristaltic micropump. An optimized bimorph bending actuator has been designed to deform the polymer membranes in an optimal and most-efficient way. The piezoelectric actuators of the micropump are driven with actuation voltages of ±260 V. The pump has a total size of 46 × 18 × 4 mm, is produced by hot embossing and is assembled in a very simple way. The presented design is able to pump water with a flow rate of 4.8 ml/min and achieves a maximum back pressure of app. 200 mBar.

Stochastic Evaluation and Analysis of Free Vibrations in Simply Supported Piezoelectric Bimorphs

Piezoelectric bimorph benders are a particular class of piezoelectric devices, which are characterized by the ability to produce flexural deformation greatly larger than the length or thickness deformation of a single piezoelectric layer. Due to extensive dimensional reduction of devices and to the high accuracy and repeatability requested, the effect of erroneous parameter estimation and the fluctuation of parameters due to external reasons, sometimes, cannot be omitted. As such, we consider mechanical, electrical and piezoelectric parameters as uniformly distributed around a nominal value and we calculate the distribution of natural frequencies of the device. We consider an analytical model for the piezoelectric bimorph proposed in literature. The results show how the parameters errors are reflected on the natural frequencies and how an increment of the error is able to change the shape of the frequencies distribution.

Enhancement of Optical Adaptive Sensing by Using a Dual-Stage Seesaw-Swivel Actuator with a Tunable Vibration Absorber

Technological obstacles to the use of rotary-type swing arm actuators to actuate optical pickup modules in small-form-factor (SFF) disk drives stem from a hinge’s skewed actuation, subsequently inducing off-axis aberrations and deteriorating optical quality. This work describes a dual-stage seesaw-swivel actuator for optical pickup actuation. A triple-layered bimorph bender made of piezoelectric materials (PZTs) is connected to the suspension of the pickup head, while the tunable vibration absorber (TVA) unit is mounted on the seesaw swing arm to offer a balanced force to reduce vibrations in a focusing direction. Both PZT and TVA are designed to satisfy stable focusing operation operational requirements and compensate for the tilt angle or deformation of a disc. Finally, simulation results verify the performance of the dual-stage seesaw-swivel actuator, along with experimental procedures and parametric design optimization confirming the effectiveness of the proposed system.

Modeling and Comparison of Bimorph Power Harvesters with Piezoelectric Elements Connected in Parallel and Series

Power harvesting devices are designed to convert the ambient energy surrounding a system to usable electric energy. The strong desire to create self-powered systems, which do not rely on traditional energy sources such as electrochemical batteries has led to the rapid growth of this field. One type of energy harvesting is the use of piezoelectric materials to directly transform ambient vibration to electrical energy. In the majority of applications the piezoelectric is configured as a bimorph bender, where the two patches of piezoceramic material can be electrically connected in either series or parallel. A reduced model will be used here to develop a set of closed form solutions to the power harvesting performance of the system based on the electrical connection of the piezoelectrics. It will be theoretically and experimentally shown that the maximum power output and efficiency is independent of the electrical connection. However, the voltage (and current) outputs between a series and parallel conditions are related by a factor of two with a symmetric system. Additionally, a critical impedance will be derived to serve as a criterion on selecting the appropriate electrical connection between the piezoelectrics to tune the systems performance based on the impedance of external circuitry. Key

CHARACTERISTICS OF SMART PIEZOELECTRIC ACTUATORS FOR PRECISE MOTION APPLICATIONS

In this paper, the static and dynamic characteristics of piezoelectric actuators (micromanipulator) are investigated theoretically and experimentally. A physical measurement setup is established for bimorph bending actuators. The actuator deflection is calculated for different driving voltages and compared with the measured values. Transient response due to a step input was very fast, the bandwidth obtained was 101Hz.The Transient, and frequency responses are obtained under different operating conditions.

Thermo-Magnetic, Piezo-Electric and Electroactive Energy Harvesting Devices

AbstractWe present three approaches to harvesting ambient energy, based on complementary physical effects in order to exploit three kinds of energy available for harvesting:Mechanical vibrationsMechanical vibration energy can be harvested with resonant mechanical structures excited by the vibrations; this scavenged energy is then transformed into electricity by piezoelectric materials. We propose to use thin piezoelectric layers deposited on the resonant structure.An on-chip integrated prototype, using a seismic mass at the end of a Si cantilever beam coated with a piezoelectric AlN film (overall volume 5 mm3), produces 30 nW of rectified power at 3 V under 0.4 g acceleration, which is enough to power a wireless sensor. Power conditioning electronics adapted to ultra-low voltage input is also proposed, which can efficiently charge a storage capacitor under very low accelerations. The fully micro-fabricated System on a Package combines a MEMS generator and ASIC power management circuit.Evolutions of ambient temperatureA permanent magnet is attached to a PZT/brass bimorph, and placed near a "thermo-magnetic" material (FeNi) which Curie temperature can be tuned around the ambient. During slow cooling or heating by the ambient air, the FeNi magnetic properties vary slowly and thus the attraction force between the FeNi and the NdFeB magnet varies slowly. Despite the slow global evolutions, the opposition between the linearity of the bimorph bending and the strong non-linearity of the magnetic attraction over distance leads to brutal clamping or release of the magnet around Tc: the piezo can then efficiently convert these fast deformations into electricity. Operational temperature range can be set by tuning the FeNi composition to obtain a predefined Curie point; hysteresis between the cooling/heating thresholds can be tuned by modifying the gap between the magnet and the FeNi.The cm-scale prototype generates a peak voltage of 35 V on release (T > Tc). For a discharge time of 0.1 s through a 1 MΩ load, the total energy harvested is 13.5 μJ per stroke, i.e. 1.35 mW of average power (respectively -14 V, 2.2 μJ and 0.22 mW on clamping when T < Tc). Output power is surprisingly constant for various load values tested. Scaling effects must now be addressed to assess the feasibility of an integrated MEMS generator and its potential efficiency.Low-frequency, large amplitude bending from human motion:A very light, flexible electro-active polymer membrane (50 x 30 mm, 31 μm thick) operates in a large frequency spectrum from quasi-static to dynamic range. It scavenges 0.1 mJ per cycle at 1 Hz, under 170 V and constant charge Q: 100 μW is enough to supply a low-power system.Improvements under investigation include achieving poling voltage with piezoelectric polymer or electrets polymer, using multi-stack scavengers to miniaturize the structure and to decrease the poling voltage V, and integration into textile.

Non-linear electromechanical behaviour of piezoelectric bimorph actuators: Influence on performance and lifetime

Piezoelectric bimorph bender actuators find application number of areas, ranging from automotive to health care. High voltage operation in harsh environments poses ever more stringent demands on functionality and lifetime. In these high performance benders, the trade-off between functionality and lifetime becomes of increasing importance, and a model-based understanding is imperative for further tailoring actuator performance. An important issue in this is the non-linear electromechanical coupling and mechanical poling/depoling processes. PZT materials are known to exhibit non-linear stiffness when strained. This effect is attributed to domain re-orientation and can result in mechanical depoling. In bimorph benders where only one of the PZT members is actuated, the non-linear stiffness effect results in higher deflections than are predicted by linear elastic models. This effect is larger for soft PZT materials than for hard PZT materials. In this work, the non-linear behaviour of piezoelectric bimorphs was characterized by dynamic mechanical thermal analysis (DMTA). Unimorph benders were characterized in different configurations. Two different PZT materials (one soft, one hard) were used. The non-linear stiffness behaviour is included in a model for piezoelectric multimorphs. The multimorph model predictions are compared to measured deflection and blocking force of bimorph benders made from soft PZT material. The model incorporating non-linear stiffness predicts deflection and blocking force values more accurately than the linear model for the situation studied. Attention is paid to the stresses induced during poling of the bimorphs and their effect on performance and lifetime. © 2008 Springer Science+Business Media, LLC.

Post-buckled precompressed elements: a new class of control actuators for morphing wingUAVs

This paper describes how post-buckled precompressed (PBP) piezoelectric benderactuators are employed in a deformable wing structure to manipulate its camberdistribution and thereby induce roll control on a subscale UAV. By applying axialcompression to piezoelectric bimorph bender actuators, significantly higher deflectionscan be achieved than for conventional piezoelectric bender actuators. Classicallaminated plate theory is shown to capture the behavior of the unloaded elements. ANewtonian deflection model employing nonlinear structural relations is demonstrated topredict the behavior of the PBP elements accurately. A proof of concept 100 mm(3.94′′) span wing employing two outboard PBP actuator sets and a highly compliantlatex skin was fabricated. Bench tests showed that, with a wing chord of 145 mm(5.8′′) and an axialcompression of 70.7 gmf mm−1, deflection levels increased by more than a factor of 2 to15.25° peak-to-peak, with a corner frequency of 34 Hz (an order of magnitude higher thanconventional subscale servoactuators). A 1.4 m span subscale UAV was equippedwith two PBP morphing panels at the outboard stations, each measuring 230 mm(9.1′′) in span. Flight testing was carried out, showing a 38% increase in roll control authorityand 3.7 times greater control derivatives compared to conventional ailerons. The solid statePBP actuator in the morphing wing reduced the part count from 56 down to only 6,with respect to a conventional servoactuated aileron wing. Furthermore, powerwas reduced from 24 W to 100 mW, current draw was cut from 5 A to 1.4 mA,and the actuator weight increment dropped dramatically from 59 g down to 3 g.

Economic application of piezoelectric actuator in linear vibratory feeding

The research investigated a decoupled vibratory feeding scheme driven by a piezoelectric actuator. In the decoupled design, the action of the horizontal and vertical vibration would be separately controlled to achieve a desired track trajectory and consequently the feed of the part. A computer control method was used to develop voltage input waveforms to control these actuators to produce decoupled movements that cause parts to move forward relative to the track and overcome backsliding and other inefficient feeding motions of conventional operation. To provide a commercial result from research, the authors proposed an economic application of decoupled feeding in an industrial environment, in which a regular PZT bimorph bender is used to drive a linear vibratory feeder in micro-industry. The bimorph actuator is economic and easy to install; however, it needs to be properly controlled to obtain the desired actuation. In the present work, a simple but effective control algorithm was designed to suppress undesired responses of the bimorph actuator, i.e. the disturbance from the harmonic vibration and hysteresis effect. The control algorithm was then downloaded into an ECM for experimental operation. The vibratory feeding effect was then studied to validate the application of decoupled piezoelectric actuation.