Piezoelectric Bending Actuators Research Articles

Ultrahigh Electrobending Deformation in Lead-Free Piezoelectric Ceramics via Defect Concentration Gradient Design.

Recent breakthroughs in defect-engineered lead-free piezoelectric ceramics have reported remarkable electrostrain values, surpassing the limit of lattice distortion. This has aroused wide concern on bending deformation and the associated underlying mechanism. Herein, via designing lead-free piezoelectric ceramics with varying volatilization characteristics, it is uncovered that the ultrahigh electrobending deformation is primarily attributed to a large strain gradient induced by unevenly distributed defect dipoles. In 0.5 mm thick Sr/Sn co-doped potassium sodium niobate ceramics featuring volatile K/Na elements, the inherent bipolar electrostrain value can reach 0.3% at 20kV cm-1 due to the existence of defect dipoles, while the gradient distribution of defect dipole generates significant bending displacement, amplifying apparent electrostrain value to 1.1%. Notably, nonvolatile Ba0.99TiO2.99 ceramic with homogeneous defect dipole distribution does not present electrobending. Of particular interest is that the electrobending phenomenon can be observed through introducing a defect dipole gradient into barium titanate ceramic. A monolayer ceramic with defect dipole gradient can generate large tip displacement (±1.5mm) in cantilever structure, demonstrating its promising potential in precise positioning. This study delves into the underlying mechanism driving electrobending deformation and its impact on the apparent electrostrain measurement in defect-engineered piezoelectric ceramics, providing fresh perspectives for the development of piezoelectric bending actuators.

Motion Characteristics of Self-Sensing Piezoelectric Actuator for Yarn Micro-Gripper

In order to solve the problem of low response frequency and poor consistency of conventional yarn grippers in weft accumulators, in this study, a piezoelectric yarn gripper is used instead of conventional yarn grippers and the motion characteristics of its actuator are studied. This gripper uses a bimorph piezoelectric bending actuator with a low-cost, well integrated self-sensing method based on charge measurement. The modeling of the piezoelectric micromanipulator is based on the piezoelectric and Euler–Bernoulli beam equations. The static and dynamic characteristics of the piezoelectric actuator as well as the self-sensing capability were experimentally tested. The experimental results show that the maximum output displacement at the end of the piezoelectric actuator is 834 μm, and the maximum output force is 388 μN at 150 V driving voltage. The stability and consistency of its response are also very good, with a response speed of 24 ms. The self-sensing test of the output force also proved the feasibility of the self-sensing method used, with an error of 0.74%. The piezoelectric yarn gripper studied in this paper is promising for practical clamping applications.

Diagnostics of Piezoelectric Bending Actuators Subjected to Varying Operating Conditions

In applications of piezoelectric actuators and sensors, the dependability and particularly the reliability throughout their lifetime are vital to manufacturers and end-users and are enabled through condition-monitoring approaches. Existing approaches often utilize impedance measurements over a range of frequencies or velocity measurements and require additional equipment or sensors, such as a laser Doppler vibrometer. Furthermore, the non-negligible effects of varying operating conditions are often unconsidered. To minimize the need for additional sensors while maintaining the dependability of piezoelectric bending actuators irrespective of varying operating conditions, an online diagnostics approach is proposed. To this end, time- and frequency-domain features are extracted from monitored current signals to reflect hairline crack development in bending actuators. For validation of applicability, the presented analysis method was evaluated on piezoelectric bending actuators subjected to accelerated lifetime tests at varying voltage amplitudes and under external damping conditions. In the presence of a crack and due to a diminished stiffness, the resonance frequency decreases and the root-mean-square amplitude of the current signal simultaneously abruptly drops during the lifetime tests. Furthermore, the piezoelectric crack surfaces clapping is reflected in higher harmonics of the current signal. Thus, time-domain features and harmonics of the current signals are sufficient to diagnose hairline cracks in the actuators.

Model-based condition monitoring of piezoelectric bending actuators

Model-based condition monitoring of piezoelectric bending actuators

MiGriBot: A miniature parallel robot with integrated gripping for high-throughput micromanipulation.

Although robotic micromanipulation using microtweezers has been widely explored, the current manipulation throughput hardly exceeds one operation per second. Increasing the manipulation throughput is thus a key factor for the emergence of robotized microassembly industries. This article presents MiGriBot (Millimeter Gripper Robot), a miniaturized parallel robot with a configurable platform and soft joints, designed to perform pick-and-place operations at the microscale. MiGriBot combines in a single robot the benefits of a parallel kinematic architecture with a configurable platform and the use of soft joints at the millimeter scale. The configurable platform of the robot provides an internal degree of freedom that can be used to actuate microtweezers using piezoelectric bending actuators located at the base of the robot, which notably reduces the robot's inertia. The soft joints make it possible to miniaturize the mechanism and to avoid friction. These benefits enable MiGriBot to reach a throughput of 10 pick-and-place cycles per second of micrometer-sized objects, with a precision of 1 micrometer.

S2worm: A Fast-Moving Untethered Insect-Scale Robot With 2-DoF Transmission Mechanism

Designing terrestrial insect-scale robot with high maneuverability and autonomy is becoming an essential challenge in the field of robotics research. Previous work has indicated that compact transmission and integrated control devices can improve the application potential. In this work, an untethered insect-scale inchworm robot is designed and fabricated by using screw theory and smart composite microstructure method, and is named S²worm. The robot weighs 4.34 g and spans 4.1 cm in length. The robot is equipped with custom designed onboard control system and high voltage boost converter to provide the driving signal for the piezoelectric bending actuator. Attributing to the novel transmission mechanism with two degrees of freedom designed based on screw theory, the S²worm can be fabricated through the smart composite microstructure method easily and shows high mobility such as high crawling speed (27.4 cm/s, 6.7 body length/s) and small turning radius (1.7 cm, 0.4 body length/s). The S²worm holds the following advantages: small size, untethered, high mobility and low energy consumption. The robot is promising for application in planetary exploration, earthquake search and constructing insect-scale multi-robot system.

A piezoelectric MEMS loudspeaker for in-ear and free field applications lumped and finite element models

This paper presents the simulation results of a piezoelectric MEMS loudspeaker. The micro-fabricated device is composed of two wafers, the first one features two bending piezoelectric actuators with large displacements, and the second one features a mobile rigid plate surrounded by a small interstice providing a thermoviscous layer hence avoiding an acoustic short circuit between its front and back sides. Performances of the loudspeaker are evaluated using a lumped element model and a finite element model to estimate the pressure generated by the loudspeaker in free field and in an ear-occluded coupler. Size variants of the design and their models are presented. The current design allows a radiated pressure of 80 dBSPL from 500 Hz at 10 cm and at 30 Vpp for a 64 mm2 footprint in free field, and more than 130 dBSPL in a IEC 60318–4 coupler with the same actuation voltage, which is above the known performances of the state of the art for MEMS loudspeakers with such dimensions.

Theoretical and experimental analyses of a legged piezoelectric bending actuator with shoe soles made of polyimide composites

Friction materials form a critical component of piezoelectric actuators, and wear of the material affects output and service life of the actuator. This paper examines the influence of polyimide (PI) composites when used as a friction material on the performance of a legged piezoelectric bending actuator. We design and manufacture demountable shoe soles, made of a novel PI-based friction material, for an actuator. A Coulomb friction model is also established to determine the behavior resulting from contact-induced friction between the surface and the actuator. Reciprocating wear tests involving an insulation rubber pad against phosphor bronze and PI composites as friction materials yielded average friction coefficients of 0.21 and 0.28, respectively. We also found that PI composites have higher wear resistance than phosphor bronze, with a specific wear rate of 1.36 × 10-4mm3/N m. The results of experiments and simulations indicate that the shoe soles made of PI composites reduced the actuator's driving frequency and vibrational amplitude, but they did not affect the principle of locomotion of the actuator. Furthermore, the operational stability of the actuator improved by 46.8% by using the demountable shoe soles made of PI composites, albeit at the cost of its velocity and load capacity. This work has guiding significance for the design and selection of friction materials for piezoelectric actuators.

Position and force sensing using strain gauges integrated into piezoelectric bender electrodes

This article derives design guidelines for integrating strain gauges into the electrodes of piezoelectric bending actuators. The proposed sensor can estimate the actuator tip displacement in response to an applied voltage and an external applied tip force. The actuator load force is also estimated with an accuracy of 8% full scale by approximating the actuator response with a linear model. The applications of this work include micro-grippers and pneumatic valves, which both require the measurement of deflection and load force. At present, this is achieved by external sensors. However, this work shows that these functions can be integrated into the actuator electrodes.

A modified sensorless position estimation approach for piezoelectric bending actuators

Piezoelectric bending actuators are widely used in micro positioning tasks. Due to material nonlinearities such as hysteresis and creep, the position-force control of these actuators is necessary. However, position sensors for micro scale applications are expensive and require a complex configuration. Sensorless approaches are alternative methods in which by resorting to the linear charge-position characteristic, the actuator position can be estimated. But, in piezoelectric actuators with small impedances, due to charge leakage caused by piezoelectric internal resistance, the charge-position characteristic is not linear. Due to nonlinear behavior of piezoelectric internal resistance, its compensation would be more complicated. This paper targets at a modified procedure in which with the help of nonlinear functions for the internal resistance, the linear charge-position characteristic can be obtained. To this purpose, a modified active Prandtl-Ishlinskii (PI) operator is proposed which estimates and compensates the charge leakage. As a result, the ideal linear mapping can be achieved and actuator position can be appropriately estimated. The results are finally validated by experiments and compared with previous methods.

Frequency and Bandwidth Tunable mm-Wave Hairpin Bandpass Filters Using Microfluidic Reconfiguration With Integrated Actuation

Microfluidically reconfigurable radio-frequency (RF) devices in general have been found attractive for low-loss, wide-frequency tunability and high-power-handling capabilities. Recently, integrated actuation of the microfluidically reconfigurable devices has been proposed for compact mm-wave device applications. This article for the first time introduces microfluidically reconfigurable frequency- and/or bandwidth-tunable bandpass filters (BPFs) operated at the mm-wave band with integrated actuation. The BPFs consist of coupled hairpin resonators. Frequency tuning is achieved by capacitively loading the resonators. Bandwidth tuning is achieved by creating varying capacitive loading among the resonators to control the interresonator couplings. The capacitive loading mechanisms are realized using the selectively metallized plates (SMPs) that can be repositioned within the microfluidic channels. The microfluidic channels are located directly above the stationary metallizations of the filter. Piezoelectric bending actuators placed under the filter's ground plane provide the SMP motion capability. The BPFs perform with the worst-case insertion loss of 3.1 dB. Frequency-tuning capable filters operate within 28-38-GHz band. Fractional bandwidth tunability varies from 7.8% to 16.7% at 38 GHz and 7.6% to 12.5% at 28 GHz for the filter that is capable of both tuning mechanisms. The filters are characterized to handle 5 W of the continuous RF power without needing thick ground planes or heat sinks. In addition, the frequency-tuning speed is characterized to be 285 MHz/ms.

Analysis of the nonlinear hysteresis of the bimorph beam piezoelectric bending actuator for the deformable mirror systems

We propose an analytical nonlinear hysteresis model of the bimorph beam bending piezoelectric actuator for a deformable mirror system. An explicit solution is derived from the analytic method based on the nonlinear elasticity. As an application example, the nonlinear hysteresis behaviors of a bimorph beam bending piezoelectric actuator, which is sandwich compounds consisting of a lower and an upper piezoelectric ceramic (PZT8-50) layer and a middle layer made of the aluminum alloy, are examined with the model. The numerical calculations based on the analytical solution are presented. The numerical simulations have shown that the nonlinear hysteresis behaviors of the bending actuator are depended on the start values of the exciting electric field and the geometric parameters of the metallic layer. In addition, the numerical results have also shown that the thickness of metallic layer has little influence on the relative hysteresis, and the relationships between relative hysteresis Δd / ΔD and the driving electric field | Estart | are linear.

A steerable miniature legged robot based on piezoelectric bending actuators

Micro robots, due to their light weight, small size and high mobility, can explore narrow space or hazardous locations that humans or larger robots cannot reach. Consequently, both academia and industry are concerned with the development of advanced microrobots. In this paper, we design a steerable miniature legged robot (SMLR) which possesses light weight and controllable linear/steerable motion by using two piezoelectric bending actuators. Its dimensions are 35 mm × 30 mm × 9 mm (length × width × height) and mass is 9 g. User can modulate the speed, turning radius, and load capacity of the robot by simply tuning the driving voltage. The robot exhibits a speed of 330 mm s−1 and a turning radius of 102 mm upon a driving voltage of 200 V and a frequency of 8.67 kHz. Moreover, it is capable of driving a 55 g embedded mass at a speed of 20 mm s−1 under a voltage of 200 V, and its simple design is ideal for down-sizing. Further, we establish a series of open-loop control programs in a virtual instrument through LabVIEW to accurately control the behavior of the SMLR (the location error is less than 5 mm), demonstrating its great potential in practical applications such as movement in a narrow space.

High-frequency robust position control of a nonlinear piezoelectric bending actuator

Piezoelectric bending actuators have been widely used in a variety of micro- and nano-applications, including atomic force microscopy, micro assembly, cell manipulation, and in general, micro electromechanical systems. However, their control algorithms at low frequencies suffer from nonlinearities such as hysteresis in high voltages and creep in long-time static applications. Also, in high-frequency applications, especially near the actuator natural frequencies, the actuator dynamic is greatly affected by the material nonlinearity. Therefore, the control approaches based on the linear dynamic modeling cannot be effective at high frequencies. Thus, the position control of the foregoing actuators become challenging, and it has been of researchers’ interests in the last decade. In this article, the robust position control of a bimorph piezoelectric bending actuators is investigated. In this regard, based on the nonlinear constitutive equations and the Euler–Bernoulli beam theory, a nonlinear dynamic model is presented. Then, to track a desired motion trajectory, an observer-based robust position control algorithm is proposed. The proposed control methodology is able to accommodate parametric uncertainties and other un-modeled dynamics. Also, it ensures the elimination of the position tracking error in the presence of the estimated states. Finally, the tracking ability of the controller is demonstrated in an experimental study. The experimental results show that the identification of the system is properly conducted with the average error of 5.5%. Also, the efficiency of the robust controller is proved with the error of 3.7% and 4.9% in the position tracking of the actuator inside and outside of the identified region, respectively.

Nonlinear vibration analysis of piezoelectric bending actuators: Theoretical and experimental studies

Piezoelectric bimorph actuators are used in a variety of applications, including micro positioning, vibration control, and micro robotics. The nature of the aforementioned applications calls for the dynamic characteristics identification of actuator at the embodiment design stage. For decades, many linear models have been presented to describe the dynamic behavior of this type of actuators; however, in many situations, such as resonant actuation, the piezoelectric actuators exhibit a softening nonlinear behavior; hence, an accurate dynamic model is demanded to properly predict the nonlinearity. In this study, first, the nonlinear stress–strain relationship of a piezoelectric material at high frequencies is modified. Then, based on the obtained constitutive equations and Euler–Bernoulli beam theory, a continuous nonlinear dynamic model for a piezoelectric bending actuator is presented. Next, the method of multiple scales is used to solve the discretized nonlinear differential equations. Finally, the results are compared with the ones obtained experimentally and nonlinear parameters are identified considering frequency response and phase response simultaneously. Also, in order to evaluate the accuracy of the proposed model, it is tested out of the identification range as well.

Two-dimensional dynamic model of the interaction of a fluid and a piezoelectric bending actuator in a plane channel

The paper proposes a two-dimensional computer model of the fluid flow in a plane channel under the action of an applied pressure drop with a flat ceramic piezoelectric actuator immersed in it, bending in the transverse direction in proportion to the applied electric voltage. A mathematical model of the coupled liquid-piezodrive system in variational form for numerical simulation by the finite element method is proposed. Since the assignment of the Dirichlet boundary conditions for displacement in this problem, is difficult, an equivalent piezo actuator deformation scheme using the Neumann boundary conditions is constructed. The deformations and equivalent stresses of von Mises on a piezo actuator are calculated. The influence of the geometry of the channel and the hydrodynamic resistance formed by the piezo actuator on the dynamics of the fluid flow is analyzed. An algorithm is proposed for adaptive dynamic remeshing of the channel computational mesh under deformations exceeding the size of finite elements. With a symmetric control signal supplied to the piezoelectric actuator, the asymmetry of the geometry leads to a violation of the symmetry of the fluid flow within the period, both in terms of fluid flow rate and in time. In the absence of a pressure drop at low frequencies of the oscillations of the piezoelectric element (of the order of the inverse relaxation time of the velocity), the period-average liquid flow rate is nonzero and increases with increasing frequency. In the presence of an external pressure drop along the layer, the average liquid flow rate is proportional to the pressure drop; at low frequencies, it is inversely proportional to the frequency; with increasing frequency, it reaches saturation. Based on the results of numerical modeling, various variants of new microfluidic technical devices generating a fluid flow using a piezoelectric bending actuator are proposed: a micropump creating a closed-circuit flow; fluid flow regulator and fluid volume dispenser.

Active vibration control of a hoop truss structure with piezoelectric bending actuators based on a fuzzy logic algorithm

Active vibration control of large flexible space structure is a challenging topic in the system dynamics and control of spacecraft. This paper proposes a novel approach for vibration control on a large hoop truss structure, typically used as mesh satellite antenna. First, to suppress the first-order bending modal response of the hoop truss structure with an initial disturbance, a piezoelectric bending actuator with excellent bending actuation performance was carefully designed as a key component of an active vibration control system. Then, the actuating characteristics of the actuator and the dynamic equations of the active structure were analyzed and formulated based on a finite element method. In order to improve the vibration-attenuating effect of the control system, a Mamdani-type fuzzy logic algorithm was employed in a closed-loop control system. Finally, simulations and experiments were implemented to validate the effectiveness of the proposed active control approach and structure. The experimental results showed that the decay time of first-order bending modal response (around 0.34 Hz) of control system reduces by 75% compared with that of the uncontrolled system. The results demonstrate that the proposed active vibration control system has good application potential in controlling the bending modes of a large flexible spacecraft.

Development and characterization of thinned PZT bulk technology based actuators devoted to a 6-DOF micropositioning platform

Piezoelectric actuators are widespread in the design of micro/nanorobotic tools and microsystems, as they have a very interesting electromechanical coupling factor, in addition to their high dynamics and resolution performances. Studies toward the integration of such actuators in complex micromechatronic systems require the size reduction of these actuators while retaining a wide range of performances. Two main fabrication processes are currently used for the fabrication of piezoelectric actuators, providing very different behaviors: (i) the use of a bulk layers and (ii) the use of thin film growth. In this study, we propose to develop micropositioning actuators and platform whose performances are a trade-off between the performances from these two technologies. The proposed trade-off technology allows the development of microsystems with high stiffness, high torque and high dynamics (from technology (i)), as well as, large motion, low voltage and small size (from technology (ii)). Using this technology we designed and fabricated a thick film PZT platform containing eight unimorph beam bending actuators. The Platform allows a high level of performances, both in the static (displacement) and dynamic (first resonance frequency) regimes. The purpose of the fabricated platform is to improve the micromanipulation and microassembly processes, to the point where approaching and manipulating very small object with a high precision will be a very fast and simple operation. These devices were obtained through a room temperature mechanical thinning of a PZT thick layers, after the deposition of Nickel on the bottom side. The piezoelectric beam bending actuators have a 80 μm thick PZT layer on top of a 10 μm thick Nickel layer, a length of 5 mm and a width of 0.5 mm. Experimental characterization has shown that the static displacements obtained are in excess of 1.33 μm/V and the resonance frequencies are up to 1814 Hz, which are very convenient in high dynamics micropositioning applications such as microrobotics and microassembly tasks.

Effective Placement of a Cantilever Resonator on Flexible Primary Structure for Vibration Control Applications—Part 1: Mathematical Modeling and Analysis

In this Part 1 of a two-part series, the theoretical modeling and optimization are presented. More specifically, the effect of attachment location on the dynamics of a flexible beam system is studied using a theoretical model. Typically, passive/active resonators for vibration suppression of flexible systems are uniaxial and can only affect structure response in the direction of the applied force. The application of piezoelectric bender actuators as active resonators may prove to be advantageous over typical, uniaxial actuators as they can dynamically apply both a localized moment and translational force to the base structure attachment point. Assuming unit impulse force disturbance, potential actuator/sensor performance for the secondary beam can be quantified by looking at fractional root-mean-square (RMS) strain energy in the actuator relative to the total system, and normalized RMS strain energy in the actuator over a frequency band of interest with respect to both disturbance force and actuator beam mount locations. Similarly, by energizing the actuator beam piezoelectric surface with a unit impulse, one can observe RMS base beam tip velocity as a function of actuator beam position. Through such analyses, one can balance both sensor/actuator performance and make conclusions about optimally mounting the actuator beam sensor/actuator. Accounting for both sensing and actuation requirements, the actuator beam should be mounted in the following nondimensionalized region: 0.4≤e≤0.5.

The milliDelta: A high-bandwidth, high-precision, millimeter-scale Delta robot.

Delta robots have been widely used in industrial contexts for pick-and-place applications because of their high precision and speed. These qualities are also desirable at the millimeter scale for applications such as vibration cancellation in microsurgery and microassembly or micromanipulation. Developing a millimeter-scale Delta robot that maintains the characteristic input-output behavior and operates with high speed and precision requires overcoming manufacturing and actuation challenges. We present the design, fabrication, and characterization of an adapted Delta robot at the millimeter scale (the "milliDelta") that leverages printed circuit microelectromechanical system manufacturing techniques and is driven by three independently controlled piezoelectric bending actuators. We validated the design of the milliDelta, where two nonintersecting perpendicular revolute joints were used to replace an ideal universal joint. In addition, a transmission linkage system for actuation was introduced to the laminate structure of the milliDelta. This 15 millimeter-by-15 millimeter-by-20 millimeter robot has a total mass of 430 milligrams and a payload capacity of 1.31 grams and operates with precision down to ~5 micrometers in a 7.01-cubic-millimeter workspace. In addition, the milliDelta can follow periodic trajectories at frequencies up to 75 hertz, experiencing velocities of ~0.45 meters per second and accelerations of ~215 meters per squared second. We demonstrate its potential utility for high-bandwidth, high-precision applications that require a compact design.