Piezoelectric Bimorph Actuator Research Articles

A Dual Stage Low Power Converter Driving for Piezoelectric Actuator Applied in Micro Mobile Robot

Piezoelectric actuators are widely utilized to convert electrical energy into mechanical strain with considerable potential in micro mobile robot applications. However, the use of Pb-based Lanthanumdoped Zirconate Titanates (PZTs) leads to two difficulties in drive circuit design, namely, high voltage step-up ratio and high energy conversion efficiency. When some devices driven by piezoelectric actuators are used in emerging technologies, such as micro mobile robot, to perform special tasks, low mass, high energy density, and high conversion efficiency are strategically important. When these demands are considered, conventional drive circuits exhibit the disadvantages of being too bulky and inefficient for low mass applications. To overcome the aforementioned drawbacks, and to address the need for a piezoelectric bimorph actuator, this work proposed a high step-up ratio flyback converter cascaded with a bidirectional half-bridge stage controlled, via a pulse width modulation strategy, and a novel control method. Simulations and experiments were conducted to verify the ability of the proposed converter to drive a 100 V-input piezoelectric bimorph actuator using a prototype 108 mg (excluding printed circuit board mass), 169 (13 × 13) mm2, and 500 mW converter.

Numerical study of active control by piezoelectric materials for fluid–structure interaction problems

Fluid–structure interaction (FSI) is a phenomenon caused by mutual interference between structures and the surrounding flow. Controlling FSI is important because FSI causes undesired vibration and it often affects the safety and lifetime of structures. Piezoelectric materials have excellent electromechanical properties to suppress vibration. As such, piezoelectric sensors and actuators are often used for reducing not only mechanical vibration but also FSI induced vibration. A number of studies have examined active control of FSI using piezoelectric materials. In the study of the control of FSI, numerical simulations are effective because they are proper for parametric studies and reduce the need for experiments. Although a number of numerical studies examined the control of FSI using piezoelectric materials, in these studies, detailed fluid analyses were not performed and the fluid force was modeled as a simple function. As such, the existing method cannot treat complicated FSI problems. Therefore, we herein propose a general-purpose system that conducts detailed electrostatic, structural, and fluid analyses and considers an active control algorithm. We design a structure–fluid–electrostatic interaction analysis system considering active control by inserting electrostatic analysis into FSI analysis solved by the partitioned iterative method and integrating the active control algorithm. In the present study, we verify the proposed system in three ways. First, while varying the material properties of the fluid, we analyze the motion of a bimorph piezoelectric actuator in a non-flowing fluid and compare the results with those of a previous study that did not take the fluid into consideration. Second, we reproduce vortex-induced vibration (VIV), which is an FSI phenomenon using the proposed system. Third, we confirm that the active control algorithm is implemented correctly by solving the suppression of VIV with the velocity feedback control. Based on these verifications, the proposed system is comprehensively proven to be correct.

Concomitant sensing and actuation for piezoelectric microrobots

Sensor fabrication for microrobots is challenging due to their small size and low mass. As a potential solution, we present a technique for estimating the velocity of piezoelectric bending bimorph actuators, a popular choice for driving such microscale devices, that requires simple electronics and no additional mechanical components. Our approach relies on the insight that motion of the actuators causes varying strains on the surface on the piezoelectric material, which via the direct piezoelectric effect, results in a current proportional to the actuator velocity. We propose that the actuator be electrically approximated as a parallel combination of a frequency and voltage dependent resistor and capacitor, and a velocity proportional current source. We develop an experimental procedure to measure these quantities, and are able to experimentally determine the actuator tip velocity to within 10% accuracy over a range of voltages (25–200 V) and frequencies (1–2000 Hz, well beyond actuator resonance). We successfully apply this sensing methodology to two microrobots, the RoboBee and the Harvard Ambulatory MicroRobot (HAMR), to estimate the wing and limb motion respectively. We further use sensor feedback to close the loop on HAMR’s leg phase and obtain desired leg trajectories near transmission resonance. The proposed sensor methodology is generic and can be applied to piezoelectric actuators of different geometries and configurations for uses in microrobotic applications.

Micro converter with a high step-up ratio to drive a piezoelectric bimorph actuator applied in mobile robots

In this study, a micro converter for driving a piezoelectric actuator is designed and implemented. The converter can produce 100 V, 80 Hz AC voltage from 3.7 V DC voltage. With regard to the requir...

Design and experiment of a small-scale walking robot employing stick-slip motion principle.

We describe the design and control of a four legged walking robot, 45 g in weight and 130 mm × 105 mm × 25 mm in size. Each leg consists of two piezoelectric bimorph actuators that are bonded at the free end by a flexure and an end-effector. The robot generates stick-slip locomotion when applying sawtooth shaped voltage signals. Friction between legs and a contact surface is analyzed by using the Coulomb friction model. Locomotion characteristics are measured in several experiments. The robot was driven with frequencies up to 75 Hz, and a maximum velocity of 65 mm/s was obtained at two frequencies: 45 Hz with 190 Vpp driving voltage and 60 Hz with 170 Vpp driving voltage, respectively.

Multi-objective optimization of a triple layer piezoelectric bender with a flexible extension using genetic algorithm

ABSTRACTThis article presents an electromechanical analysis for a piezoelectric bimorph actuator with a flexible extension, which is used to increase the tip deflection. The performance measuring attributes of such an actuator are derived, and a genetic algorithm is used for multi-objective optimization. The analysis reveals that for a thick flexible extension, the length of the extension provides Pareto optimal solutions for multi-objective optimization. The analysis also shows that as the thickness of the flexible extension decreases, the Pareto optimal solutions converge to a single solution for multi-objective optimization. We have considered nonlinear deflection behavior of piezoelectric materials at high electric fields, and series and parallel electrical connections in the analysis.

Performance improvement of a piezoelectric bimorph actuator by tailoring geometry

ABSTRACTThis article illustrates performance improvement of a piezo-bimorph actuator by tailoring its geometry. We have analytically presented that a piezo-bimorph actuator with a tapered surface provides superior performance for out-of-plane bending compared to a rectangular surface while having equal mass and equal primary capacitance. Equal capacitance ensures equal input electrical energy and bandwidth for both the cases below its first resonant frequency. We have analytically derived performance measuring attributes of such an actuator considering high electric field, and shown the performance improvement quantitatively. We have also presented finite element solutions to compare with the analytical solutions. Some results are validated with the earlier published experimental results.

Experimental characterizations of bimorph piezoelectric actuator for robotic assembly

Piezoelectric actuator is one of the most versatile types of smart actuators, extensively used in different industrial applications like robotics, microelectromechanical systems, micro-assembly, biological cell handling, self-assembly, and optical component handling in photonics. By applying potential to a piezoelectric actuator, it can produce micro level deflection with large force generation, very fast response, and long-term actuation as compared to other actuators. The design and analysis of the bimorph piezoelectric cantilever using proportional–integral controller are carried out where the bimorph piezoelectric actuator is used as an active actuator for providing the dexterous behavior during robotic assembly. Characterization of bimorph piezoelectric actuator carried out by controlling voltage signal provides steady-state behavior which is verified by conducting experiments. A prototype of micro gripper is also developed which shows the potential of handling small lightweight objects for robotic assembly.

Experimental performance evaluation of smart bimorph piezoelectric actuator and its application in micro robotics

Piezoelectric actuator is one of the most versatile types of smart material based actuators which can be utilized for different industrial applications like robotics, MEMS, micro assembly, biological cell handling, self-assembly and optical component handling in photonics. By applying a potential to piezoelectric based smart actuator, it can produce micro level deflection with large force generation, very fast response and long term actuation as compared to other actuators. The characterization and performance evaluation of the bimorph piezoelectric cantilever beam using novel fuzzy logic controller (FLC) tuned proportional-integral-derivative (PID) system has been carried out where the smart bimorph piezo actuator is used as an active actuator for providing the dexterous behavior during robotic assembly. Fuzzy is introduced for fast tuning of PID and it provides the steady state characteristics. Experimentally, it is verified that the actuator produces steady state behavior of deflection for handling the object. A prototype is developed which shows the potential of handling the light weight objects for assembly.

Effect of self-induced electric displacement field on the response of a piezo-bimorph actuator at high electric field

This paper analytically illustrates the response of a piezoelectric bimorph actuator considering the effect of self-induced electric displacement field. In the analysis, we have considered response of the actuator at high electric field. The self-induced electric displacement field exists inside the piezoelectric actuator during its bending. This effect was not considered in the earlier modeling, which typically followed stress-strain based approaches, instead of following the extended Hamilton's principle for electromechanical systems driven by constant voltage source. This electric displacement field affects the tip deflection of a piezoelectric actuator. The new derivation based on Hamilton's principle also shows that a piezo-bimorph's short circuit stiffness, which was considered independent of the piezoelectric coupling coefficient in earlier literature, actually depends on the piezoelectric coupling coefficient. A piezoelectric material of high piezoelectric coupling coefficient can produce a significant self-induced electric displacement field, which can significantly impact the tip deflection and the stiffness of a piezoelectric bimorph actuator. The analytical results are validated with the experimental results, published in earlier literature.

A miniature circular pump with a piezoelectric bimorph and a disposable chamber for biomedical applications

Piezoelectric miniature pumps provide excellent stability and accuracy, and thus, have been used in fluid handling and medical applications. In the current study, a separable piezoelectric miniature pump was developed by combining a piezoelectric bimorph actuator and a disposable pumping chamber. By employing a single-use disposable pumping chamber the cross-contamination issues caused by repeated uses of the pumping chamber can be easily avoided, making the pump ideal for biological fluid transmission process. The pumping in the proposed miniature pump was indirectly driven by a circular piezoelectric bimorph actuator through a pillar structure that connects the actuator with the covering PET diaphragm of the pumping chamber. The pumping efficiency of the proposed miniature pump was investigated with respect to several parameters, such as the diaphragm thickness, the chamber diameter and the pillar-to-chamber ratio. A maximum flow rate of 9.1mL/min was achieved by using the proposed pump structure with 10mm chamber diameter and a pillar-to-chamber ratio of 0.9.

Size-dependent constituent equations of piezoelectric bimorphs

In this paper, two size-dependent constituent equations for symmetrical/heterogeneous piezoelectric bimorph actuators are developed using the modified couple stress theory and the principle of minimum total potential energy. The present model involves an internal material length scale parameter used to capture the size effect. In the limit when the internal material length scale parameter goes to zero, this model reduces to classical (local) constituent equations available in the literatures. Exact solutions for the normalized static deflection are obtained as a function of the ratio of the actuator thickness to the internal material length scale parameter. The simulations show that the static deflection developed by the present model has a remarkable difference with those got by the classical constituent equations when the ratio of the beam thickness to the internal material length scale parameter is small. It is also observed that the stiffness of elastic layers show directionally opposite effects on tip deflections of symmetrical piezoelectric bimorph actuator and heterogeneous one.

Modelling and analysis of circular bimorph piezoelectric actuator for deformable mirror

A theoretical model of a circular flexure-mode piezoelectric bimorph actuator is established. The circular bimorph structure, consisting of two flexible layers of piezoelectric material and a layer of metallic material in the middle, is powered to the flexural deformation. The analytical solutions including the statics solution and the dynamics solution are derived from the 3D equations of the linear theory of piezoelectricity. Numerical results are included to show the circular bimorph piezoelectric actuator (CBPA) performance, depending on the physical parameters.

Multilayer laminated piezoelectric bending actuators: design and manufacturing for optimum power density and efficiency

In previous work we presented design and manufacturing rules for optimizing the energy density of piezoelectric bimorph actuators through the use of laser-induced melting, insulating edge coating, and features for rigid ground attachments to maximize force output, as well as a pre-stacked technique to enable mass customization. Here we adapt these techniques to bending actuators with four active layers, which utilize thinner material layers. This allows the use of lower operating voltages, which is important for overall power usage optimization, as typical small-scale power supplies are low-voltage and the efficiency of boost-converter and drive circuitry increases with decreasing output voltage. We show that this optimization results in a 24%–47% reduction in the weight of the required power supply (depending on the type of drive circuit used). We also present scaling arguments to determine when multi-layer actuator are preferable to thinner actuators, and show that our techniques are capable of scaling down to sub-mg weight actuators.

Active filter driver for piezo-actuators for flapping-wing micro air vehicles

Piezoelectrically actuated flapping-wing micro air vehicle (MAV) is an emerging technology. This paper discusses limitations of presently used voltage drivers for the piezoelectric actuators used in such applications and suggests an active filter-based unipolar high-voltage driver. A Chebyshev polynomial has been used to extract a unipolar sinusoidal high voltage signal from a unipolar square wave signal for driving the piezoelectric actuators at low frequency in flapping-wing MAV applications. The filter is based on Sallen–Key topology and is suitable for connecting a piezo-bimorph in series or parallel electrical connection. We have considered an application-specific piezoelectric bimorph actuator of 40 Hz flapping frequency and 32 nF capacitance in each piezoelectric layer to design a driver. The driver circuit in verified by simulation results of OrCAD® software. The driver circuit can control the frequency of the sinusoidal driving voltage, which causes wing-flapping, by radio control communication.

Theoretical analysis on shear-bending deflection of a ring-shape piezoelectric plate

In this paper, the electromechanical coupling field in shear-bending mode for a ring-shape piezoelectric plate was theoretically established. According to the classical small bending elastic plate theory and piezoelectric constitutive equations, the analytical solution to the bending deformation of the piezo-actuator under electric field and a concentrated or uniformly distributed mechanical load was achieved. The mechanism for generating bending deformation is attributed to axisymmetric shear strain, which further induces the bending deformation of the single ring-shape piezoelectric plate. This mechanism is significant different from that of piezoelectric bimorph or unimorph actuators reported before. Our analysis offers guidance for the optimum design of a ring-shape shear-bending piezo-actuator.

Modeling and analysis of the thermal effects of a circular bimorph piezoelectric actuator

A theoretical analysis of the thermal effects of a circular bimorph piezoelectric actuator (CBPA) was performed. The circular bimorph structure consists of two flexible piezoelectric ceramic layers and one metallic layer in the middle, and is powered to produce flexural deformation. The CBPA, which may be a good match for large adaptive optics telescopes, has a large stroke and a high resonance frequency. We have derived analytical solutions (both the static solution and the dynamic solution) of the thermal effects of introducing (and increasing the thickness of) a metallic layer into the bimorph. Numerical results are presented to illustrate the dependence of the CBPA's performance upon the physical parameters.

Electromechanical analysis of piezoelectric bimorph actuator in static state considering the nonlinearity at high electric field

ABSTRACTThis article contains electromechanical analysis of a piezoelectric bimorph actuator at high electric field by incorporating second-order constitutive equations of piezoelectric material. Tip deflection, block force, block moment, block load, output strain energy, output energy density, input electrical energy, and energy efficiency are analytically derived for the actuator at high electric field. The analysis shows that output energy and energy density increase more rapidly at high electric field, compared to the prediction by the linear model. The analysis shows energy efficiency depends on electric field. Some analytical results are validated with the published experimental results.

A comparative study of piezoelectric unimorph and multilayer actuators as stiffness sensors via contact resonance

Piezoelectric bar-shaped resonators were proposed to act as hardness sensors in the 1960s and stiffness sensors in the 1990s based on the contact impedance method. In this work, we point out that both multilayer and unimorph (or bimorph) piezoelectric actuators could act as stiffness/modulus sensors based on the principle of mechanical contact resonance. First, the practical design and the performance of a piezoelectric unimorph actuator–based stiffness sensor were presented. Then the working principle of piezoelectric multilayer actuator–based stiffness sensors was given and verified by numerical investigation. It was found that for these two types of resonance-based sensors, the shift of the resonance frequency due to contact is always positive, which is different from that of the contact impedance method. Further comparative sensitivity study indicated that the unimorph actuator–based stiffness sensor is very suitable for measurement on soft materials, whereas the multilayer actuator–based sensor is more suitable for hard materials. Both multilayer (or bar-shaped) and unimorph (bimorph) piezoelectric actuators can be used as stiffness/modulus sensors based on the mechanical contact resonance.

Analytical analysis of a beam flexural-mode piezoelectric actuator for deformable mirrors

A beam flexural-mode piezoelectric bimorph actuator is analyzed based on linear piezoelectricity, and the performance of the actuator is studied. The beam bimorph piezoelectric actuator (BBPA), which is a sand- wich compound consisting of a lower and an upper piezoelectric ceramic surface layer and a middle layer made of metal, is driven to flexural deformation. The statistical analytical solution and dynamical solutions from the three-dimensional equations of linear piezoelectricity are derived, and the dependence of the performance upon the physical parameters of the BBPA is evaluated. Numerical results illustrate the strengthened performance achieved by adjusting the geometrical and material parameters of the BBPA.©2015SocietyofPhoto-OpticalInstrumentation