Piezoelectric Stack Actuator Research Articles

A novel three-phase excitation piezoelectric motor for macro-micro actuation: integration design, systematic modeling, and experimental evaluation

Macro-micro actuators require complex feedback control systems to obtain high positioning cooperativeness. However, the mechanical connections of macro-micro actuators are generally redundant in terms of their size, which is highly unfavorable for both miniaturization and integration. This paper presents an approach to address this problem based on a novel integration design for a three-phase excitation piezoelectric motor (TPM) that is capable of performing macro-micro actuation by switching its operating mode from resonant to nonresonant. The load capacity of the proposed TPM can reach 0.39 Nm with a maximum speed of 3.82 rad s−1 (36.5 rpm). This performance is achieved by using a unique triangular flexible stator that contains three piezoelectric stack actuators acting as vibrators and is excited by a three-phase electrical signal. A time-domain electromechanical coupling dynamic model is developed to determine the dynamic behavior of the proposed motor, and the modeling results are validated successfully by experimental results obtained from a fabricated prototype. The proposed motor is expected to be helpful for integration design of piezoelectric devices that require macro-micro actuation.

Active Global Vibration Control of Helicopter Fuselage

Active control of structural response (ACSR) has been widely used to suppress helicopter fuselage vibration due to its advantages. However, ACSR, by taking the vibration responses at target measurement points as the active control objective, is a local vibration control method for the fuselage. In this paper, an active global vibration control (AGVC) method for the fuselage by taking the vibratory loads transmitting to the fuselage through gearbox struts as the active control objective is proposed. By installing piezoelectric stack actuators on a gearbox strut, the active strut is formed and its electromechanical coupling equation of motion is derived. The AGVC model, algorithm, convergence, and system for a dynamically similar frame structure of a helicopter fuselage are presented. The simulation results indicate that AGVC can suppress the global vibration of the fuselage under the excitation of the rotor vibratory loads more effectively with faster convergence speed than ACSR. The vibration at the target measurement points in ACSR can be effectively reduced, but the control effect at other positions is not satisfied, and even the vibration at some positions is larger than that in control off.

A Miniaturized Piezo Stack Impact Actuation Mechanism for Out-of-Plane Freely Moveable Masses.

We present the prototype and analytical model of a miniaturized impact actuation mechanism, providing a fast out-of-plane displacement to accelerate objects against gravity, allowing for freely moving objects and hence for large displacements without the need for cantilevers. To achieve the necessary high speed, we chose a piezoelectric stack actuator driven by a high-current pulse generator, connected to a rigid support and a rigid three-point contact with the object. We describe this mechanism with a spring-mass model and compare various spheres with different masses and diameters and from different materials. As expected, we found that larger flight heights are achieved by harder spheres, achieving, e.g., approx. 3 mm displacement for a 3 mm steel sphere using a 3 × 3 × 2 mm3 piezo stack.

Modeling of bonding piezoelectric stack using conductive adhesive with metal-coated polymer fillers

Bonding piezoelectric stack (BPS) is a common type of piezoelectric stack actuator (PSA) with an adhesive bonding layer. The regular bonding layer in BPS is produced by the dielectric materials, which may lead to electric energy dissipation and thus decrease the displacement of BPS. The dissipation can be compensated by substituting the regular bonding with the conductive adhesive (CA) using the conductive fillers, say, the metal-coated polymer fillers. In order to verify the feasibility of using this new BPS for piezoelectric devices and model-based controller designs, this paper establishes a novel BPS model using CA with metal-coated polymer fillers. In this paper, a dielectric model and a Kelvin–Voigt model are used to describe BPS’s electric and mechanical behaviors using regular bonding. A brief particle-bonding model is used to switch the BPS model using the regular bonding to the model using CA with metal-coated polymer fillers. The theoretical simulation and the experiment results demonstrate that the model has more than 97% accuracy. The results indicate that the dynamic model can accurately predict the displacement of BPS when the CA is used in conjunction with metal-coated polymer fillers and other metal-coated fillers, which can be used to design large-scale piezoelectric devices.

MIMO Multi-Frequency Active Vibration Control for Aircraft Panel Structure Using Piezoelectric Actuators

Undesirable vibration of aircraft panel structures has a significant impact on the safety of their occupants and the operational reliability of various systems. The traditional time-domain controller based on the parallel multi-frequency filtered-x least mean square (FxLMS) control algorithm is simple and effective. However, the mutual influence of convergence steps and the induced harmonic components will limit its performance. An improved parallel multi-input multi-output multi-frequency FxLMS (MIMOMF-FxLMS) algorithm is proposed, considering the multi-input multi-output (MIMO) control requirement of the aircraft panel structure active vibration control (AVC) system and its inevitable channel coupling phenomenon. The feedback error signal and the control channel model are processed by frequency division in the MIMOMF-FxLMS algorithm, so that the FxLMS algorithm of each control channel runs independently, effectively avoiding mutual interference between convergence steps and the generation of induced harmonic components. Simulation and experimental research on multi-frequency AVC of the panel structure model is performed using a new type of piezoelectric stack actuator. The test results show that the proposed controller reduces the vibration level of each observation point by more than 98%, and the vibration responses of the first two-order frequency component are significantly suppressed, which also has strong adaptability and anti-noise ability.

A closed loop system to control transverse deformations in LHC collimators

This work presents a novel closed-loop control system for the detection and control of thermal deformations integrated in the secondary collimators of the Large Hadron Collider (LHC). Interactions between spurious particles lost transversally from the circulating beam core and the collimator jaws that make up the active area of the collimator will result in thermally induced deformations in those jaws. This interaction can push the jaw’s straightness out of the tolerance and force the jaw either into the beam core or away from it. This action can result in reductions in beam cleaning efficiency and increases in impedance on the beam. Whilst deformations in either direction are to be avoided, deformations into the beam are considered more of an issue as too much deformation can provoke beam dumps if beam losses are too high. To minimize this unavoidable thermal effect a novel adaptive closed-loop monitoring and actuation system, comprising of multiple intrinsic Fabry–Pérot interferometric (IFPI) optical sensors, and several integrated piezoelectric stack actuators, has been developed. When operating, this system can transiently monitor the jaws straightness and when required correct for deformations up to 500μm. In addition, subsequent steps to use this system as an active damper to reduce vibratory response, as experienced when the jaw undergoes a direct beam impact, are also discussed.

Multi-directional active vibration control of 1D smart structure inspired by automotive engine mounting system

Recently, active mounting system is being gradually applied to automotive engine mounts for mitigating structure-borne vibration effectively throughout the whole vehicle chassis. This paper presents modeling, analysis, and control of a source structure with an active mounting system in multi-directions, considering position and direction of actual automotive engine mounts. The active mount consists of a piezoelectric stack actuator in series with an elastomeric (rubber) mount. When harmonic excitation forces are employed, secondary force required for each active mount is calculated mathematically and the control signal can reduce the vibration through the destructive interference with input signal. In addition, the horizontal vibration can also be mitigated by setting a variable parameter through the dynamic relation of source structure. A series of simulation results demonstrate that the excitation vibration could be reduced along with this multi-directional (vertical and horizontal) active mounts. Based on this result, it can be expected that noise vibration harshness(NVH) performance can be improved by controlling the vibration of the actual automotive engine structure with rubber mount and secondary force of actuators in both vertical and horizontal directions.

Experimental performance evaluation on piezo-hydraulic pump using flexurally amplified piezoelectric actuators

This paper presents an experimental study on a piezo-hydraulic pump using two different flexurally amplified piezoelectric (FAP) actuators. FAP actuators produce amplified displacement using piezoelectric stack actuators as prime mover. FAP376 and FAP640, having different characteristics are used as pumping actuator to pump the fluid from the piezo-hydraulic pump. The pumping chamber is made of stainless-steel metallic bellows and unidirectional valves are connected to the inlet and outlet port of the piezo-hydraulic pump. Mathematical model is developed for theoretical calculations on the flowrate of piezo-hydraulic pump. Also, pump flowrate is determined experimentally using flowmeter for two different FAP actuators and compared with the respective theoretical values. Further, performance evaluation is done by comparing the flowrate developed by the piezo-hydraulic pump at different actuation frequencies using two different FAP actuators.

Dynamic modeling and disturbance rejection compensation for hysteresis nonlinearity of high voltage piezoelectric stack actuators

High voltage piezoelectric stack actuators (HVPSA) are widely used in the field of active vibration control of engineering structures due to their strong load capacity, fast response rate, and high mechanical output efficiency. However, their inherent hysteresis will have a direct impact on the stability and control efficiency of the piezoelectric active control system. To compensate the hysteresis nonlinearity of HVPSA, a high-precision dynamic hybrid method based on linear active disturbance rejection control (LADRC) is proposed. Starting from the hysteresis analysis of piezoelectric actuators, an exponential function butterfly-shape hysteresis operator is constructed and combined with the asymmetric Bouc–Wen model to present a novel hybrid static hysteresis model. In order to implement rate-dependent hysteresis modeling, the Hammerstein rate-dependent hysteresis model of HVPSA is further established, and its inverse model is built for feedforward compensation. Subsequently, the LADRC is used to adjust the driving voltage in real time to form the hysteresis closed-loop compensator of HVPSA. The experimental results show that the Hammerstein rate-dependent hysteresis model established has satisfactory modeling accuracy in the working voltage range and frequency band under consideration. Furthermore, compared with the traditional inverse model feedforward compensation strategy, the proposed hybrid compensation method based on LADRC improves the compensation efficiency by more than 11% and reduces the hysteresis nonlinearity of HVPSA to less than 3%, with strong anti-disturbance ability.

Hysteretic behaviour and structural control performance of a piezoelectric friction damper

This study proposes a novel piezoelectric friction damper (PFD). Experiments and numerical simulations are carried out to investigate the mechanical model of the PFD, and the effects of loading speed, displacement amplitude, voltage, friction plate material, piezoelectric stack actuator dimensions, and spring parameters on the hysteretic characteristics of the PFD. Results show that the PFD attains a stable mechanical performance within the design loading speed and displacement amplitude. The piezoelectric stack actuator functioning as a friction control device, can increase friction by 54% at 120 V. In damper design, an appropriate increase of the constraint stiffness of the damper and a piezoelectric stack actuator with the same stiffness as the damper constraint can achieve greater output force, and the preload of the spring should be greater than the friction to prevent residual displacement. The PFD has better seismic performance for large-span cable dome structures than the traditional friction damper. The vertical peak displacement and acceleration reduction ratio reached 45.1% and 67.7% with PFDs, respectively. The PFD with semi-active control is suitable for large-span spatial structures.

Design of a Panoramic Scanning Device Based on a Piezoelectric Ceramic Stack Actuator and Friction Transmission

In view of the complex structure and inaccurate positioning capabilities of the existing panoramic scanning system, a panoramic scanning device based on a piezoelectric ceramic stack actuator and friction transmission was designed. In our model, the output displacement of the piezoelectric ceramics is amplified by a bridge-type flexure hinge and applied to a shaft by friction to achieve panoramic scanning imaging. The mathematical model of the device was established, and the working characteristics were analyzed. The analysis demonstrated that the linear displacement increment of the shaft is a superposition. A modality simulation was performed, and the simulation results show that the designed device works normally at a frequency of 511.5 Hz. The test results indicated that the displacement of the actuator can reach 6 μm at an input voltage of 100 V. Moreover, the laser scanning results showed that the designed device can perform panoramic scanning imaging, which meets the requirements for use on the high-speed imaging system.

Active vibration control of large space structures: Modelling and experimental testing of offset piezoelectric stack actuators

To meet demanding mission objectives, most current satellites for Earth and Universe observation are equipped with large flexible appendages. However, due to the coupling between spacecraft rigid and elastic dynamics, unwanted elastic vibrations of such flexible elements may compromise the achievement of pointing and stability requirements. Therefore, control solutions aiming at avoiding instabilities and, at worst, the failure of the mission, are currently needed. In this scenario, growing interest has been recently devoted to Active Vibration Control (AVC) strategies relying on the use of smart materials. Among them, piezoelectric patches are the most studied and tested devices for both actuating and sensing purposes. This paper aims to contribute to this line of research by investigating a different type of actuator, namely an Offset Piezoelectric Stack Actuator (OPSA), to assess its performance in damping out elastic vibrations of large space structures. Moreover, special attention is devoted to compare OPSA performance with standard patch actuators behaviour. In order to develop the AVC system, an equivalent electro-mechanical coupled Finite Element (FE) formulation is implemented, integrating both sensors and piezo-stack elements on the passive hosting structure. The final structural model including both electrical inputs/outputs, as well as modified mass and stiffness due to the additional piezo devices, is then obtained. A parametric analysis is carried out to optimize the maximum control action exerted by the OPSA device. Finally, the OPSA numerical model is experimentally validated by mounting it on a cantilever plate, representative of a scaled solar panel. Experimental data are used not only to verify the device expected functioning, but also to tune the parameters in the OPSA FE model, which can be finally integrated in a planar satellite dynamics simulator to evaluate the AVC system efficiency when performing attitude manoeuvres.

Design, fabrication, and characterization of piezoelectric single crystal stack actuators based on PMN-PT

A piezoelectric stack actuator (PSA) consisting of 28 lead magnesium niobate-lead titanate (PMN-PT) piezoelectric single crystal layers is developed. The free stroke and blocking force, which are the figures of merit of a PSA, are simulated through finite element analysis. The free stroke of the PSA samples measured using a laser displacement sensor was in the range of 6.4–8.0 µm at 200 V. In addition, the blocking force of the PSA samples measured using a custom-made system, consisting of a strain gauge, a motor and a load cell, was in the range of 191–226 N at 200 V. An analysis of seven samples exhibited that a large free stroke resulted in a blocking force of the PSA.

Round window stimulation with an interface coupler demonstrates proof of concept

HypothesisTo mechanically stimulate the round window (RW) membrane, an actuator with an interface coupler (IC) has the potential to improve sound transmission to the cochlea as compared to the most used RW stimulation device implanted today. If a proof-of-concept IC prototype shows promise as compared the most common method for RW stimulation, there is potential that future design development of an IC will be worthwhile. BackgroundA variety of hearing pathologies resulting in mixed and conductive hearing loss can be addressed by mechanically stimulating the RW to transmit sound to the cochlea. The most common method for RW stimulation is with the floating mass transducer (FMT, Med-El). However, the FMT suffers poor sound transmission and unreliable device positioning. The dynamic range and bandwidth of the FMT as a RW stimulator is limited because the entire FMT needs freedom to vibrate. Thus the FMT has difficulty overcoming its own inertia and it cannot be stabilized in a manner that may limit its motion. Here we test an idea of using a generic actuator that vibrates on one side while stationary and held stable on the other (unlike the FMT), and coupling the actuator vibration to the RW membrane with a proof-of-concept IC designed to safely transmit sound to the cochlea. We determine if this proof-of-concept IC can perform as well or better than the FMT in one specimen. If so, further developments of the IC would be worthwhile. MethodsRW sound transmission comparison was made between an ideally implanted FMT and a proof-of-concept IC prototype driven by a piezoelectric stack actuator with vibrating tip in a fresh human temporal bone. Velocities of stapes, FMT, and IC actuator were measured with laser Doppler vibrometry to determine bandwidth, linearity, and dynamic range of cochlear sound transmission. ResultsStimulation with proof-of-concept prototype of the IC provided increased sound transmission, more linear output for larger dynamic range, and wider frequency range as compared to the FMT. This experiment demonstrates the potential of the IC concept to improve performance, and that it merits further development. However, it was challenging to stabilize the coupling between an external actuator and the proof-of-concept IC prototype. Thus, although we were successful in showing that this IC concept has promise, major design improvements and developments are required in the future. ConclusionsWe demonstrated that the proof-of-concept IC prototype driven with a tip connected to a piezoelectric stack actuator can stimulate the RW membrane with improved acoustic performance as compared to the FMT in one specimen. This study demonstrated proof of concept: that the idea of an IC for sound transmission to the cochlea through the RW has potential, and that it would be worthwhile to pursue the IC idea with further developments. This idea has the potential to provide robust sound transmission to the cochlea via the RW while preventing possible trauma to the cochlea. We also learned that critical design improvements are necessary because coupling the generic external actuator to the IC was challenging. A possible future IC design is to integrate a piezoelectric actuator permanently to the IC, allowing only the soft balloon membrane of the IC to vibrate the RW while the rest of the exterior housing of the combined IC (with actuator) would not vibrate and would be stabilized in a fixed manner.

Study on Electrical Parameter Matching of Piezoelectric Stack Periodic Strut for Helicopter Cabin Noise Control

The gear meshing noise generated by the helicopter main reducer is one of the important sources of noise in the helicopter cabin. By improving the isolation performance of the struts supporting reducer to the gear meshing vibration, the purpose of reducing the gear meshing noise in the helicopter cabin can be achieved. Piezoelectric stack periodic strut (PSPS) composed of piezoelectric stacks and passive materials periodically arranged is an original type of strut with active and passive hybrid isolation characteristics. Piezoelectric stacks and passive materials form a periodic structure, which makes PSPS have a unique stopband characteristic. The propagation of elastic waves in the stopband frequency range is attenuated, which can improve the broadband passive vibration isolation capability of the PSPS; The piezoelectric stacks can adjust the elastic wave propagation in the PSPS and improve the single-frequency or multifrequency active isolation performance of the PSPS. Since the driving voltage and current range of the piezoelectric stacks significantly affect the isolation performance of the PSPS, this article focuses on the relationship between the isolation performance of the PSPS and the voltage and current required by the piezoelectric stacks. Firstly, based on the passive material periodic structure transfer matrix model, the driving voltage and current of the piezoelectric stacks are introduced into the model, and a PSPS electromechanical coupling model based on the transfer matrix form is established. Secondly, the correctness of the model is verified by the finite element software. Based on the model, the design process of PSPS parameters is proposed. The optimal isolation performance of PSPS is predicted under the limitation of maximum driving voltage and current. The effects of damping loss factor, exciting force, period number and passive material on the requirements of electrical parameters for active control are studied. A three-period PSPS strut composed of piezoelectric stack actuator and PV strut is used for experimental research, and the matching of electrical parameters of this PSPS in the test is analyzed.

Normalized Adaptive Hybrid Control Algorithms for Helicopter Vibration with Variable Rotor Speed

Variable rotor speed technology implemented in a helicopter can improve the flight performance, reduce the required power, and increase the flight speed. However, variable rotor speed changes the frequencies of rotor vibratory loads and may produce helicopter fuselage resonance under the excitation of the rotor vibratory loads. Active vibration control (AVC) has been effectively used in vibration reduction of helicopter fuselages. However, the frequency domain control algorithms that are currently used have poor adaptability in controlling vibration with variable frequencies (i.e., during time varying rotor speeds). In order to effectively improve control convergence, adaptability, and effectiveness, the normalized adaptive hybrid control algorithms containing both the normalized adaptive harmonic control algorithm and the normalized frequency tracking algorithm have been presented in this paper. Simulations of AVC with variable frequencies on a dynamically similar frame structure of a helicopter fuselage driven by piezoelectric stack actuators installed on the gearbox support struts show that the normalized adaptive hybrid control algorithms can accurately track the changes in rotor load frequencies and can be effectively used in the AVC of a helicopter with variable rotor speed.

Forced liquid cooling of piezoelectric stack actuator utilizing silicone oil

Piezoelectric stack actuators (PESAs) are usually used in applications requiring a fast response, high resolution, and high accuracy. Self-heating during continuous drive with a large voltage amplitude at high frequencies can damage PESAs and limit the driving conditions. A sufficient cooling method is necessary to increase the driving frequency and driving amplitude. This paper proposes a direct forced liquid cooling system for PESAs and experimentally and numerically evaluates the PESA temperatures when employing this cooling system. Silicone oil, which is an excellent electrical insulator, and has a high heat transfer coefficient and good stability, was selected as the coolant. The proposed forced liquid cooling can suppress the temperature rise to about 10% of that achieved through natural heat dissipation. With an input voltage amplitude of 50 Vpk at a frequency of 10 kHz, the PESA cannot be continuously driven with natural heat dissipation. Using the proposed liquid cooling, the temperature of the PESA resin coating was kept well below the upper limit given by the manufacturer. Furthermore, the internal temperature of the PESA was estimated from heat transfer analysis using a finite element model. This confirmed that the internal temperature of the PESA was lower than the Curie temperature.

Discrete-time rate-dependent hysteresis modeling and parameter identification of piezoelectric actuators

A discrete-time-modified Bouc–Wen model is proposed to describe the non-symmetrical and rate-dependent hysteresis of piezoelectric actuators for micro-vibration control applications. The modified model combines a non-symmetrical Bouc–Wen model and a frequency-dependent dynamic module. A series of experiments are conducted to characterize the rate-dependent hysteresis of piezoelectric stack actuators under sinusoidal excitations at a range of 1 to 20 Hz. The experimental results verify the validity of the modified model. The modified Bouc–Wen model increases the complexity of Bouc–Wen hysteresis nonlinear differential equation, which brings difficulties to parameter identification. To identify the parameters of Bouc–Wen model, an improved hybrid differential evolution and Jaya (DE-Jaya) algorithm is introduced with a hybrid mutant operator and Jaya operator that tried to balance between convergence speed and solution accuracy. The improved algorithm is tested on benchmark functions and compared with other optimizations to prove its effectiveness. The comparison results show that hybrid DE-Jaya algorithm has better performance in convergence speed and solution accuracy. The identified discrete-time-modified Bouc–Wen model is used as the secondary path in a filtered-x variable step-size affine projection algorithm (FXVSSAPA), and experimental verifications are done on a micro-vibration control platform. The experimental results show that the FXVSSAPA algorithm can converge to the steady-state error faster and verify the effectiveness of the proposed discrete-time-modified Bouc–Wen model.

Effect of Forced Liquid Cooling on the Voltage/Charge Displacement Characteristics of Stacked Piezoelectric Actuators during High-Frequency Drive

Piezoelectric stack actuators (PESAs) are widely used in applications requiring a fast response, high resolution, and high accuracy. The self-heating of a PESA during continuous drive with a large amplitude at high frequencies can change its voltage displacement and charge displacement characteristics. These changes can lead to a loss of stability and inaccurate PESA positioning systems. In this paper, we confirmed that by using our proposed forced liquid cooling, the changes to the dynamic characteristics and the impedance of a PESA due to the fact of self-heating could be reduced. Voltage displacement curve measurements at 10 kHz demonstrated that with natural heat dissipation, the amplitude of PESA increased by 15% due to the self-heating compared to the amplitude measured at the start of driving but only by 3% with forced liquid cooling. The displacement-to-charge ratio decreased by 12% compared to that at room temperature with natural heat dissipation, while it increased by 1% during forced liquid cooling. In the measured frequency response of the voltage displacement transfer function, the increased temperature changed the gain and phase of the first and secondary vibration modes above 20 kHz with natural heat dissipation. Forced liquid cooling also reduced the variations in the frequency response of the voltage displacement transfer function.

Measurement Range Enhancement of a Scanning Probe by the Real Time Adjustment of the Interferometer Reference Mirror

Scanning probes on the micro/nano-coordinate measuring machines (micro/nano-CMMs) can produce on/off signals and achieve 3D measurement ability within a specific range. The authors have developed several scanning probes based on a 2D angle sensor and a miniature Michelson interferometer that can work within ± $10~\mu \text{m}$ . When the probe’s lateral displacement is greater than $10~\mu \text{m}$ , the interferometer signal is easy to break, limiting the measurement range of these probes. A 2D angle fine-tuning stage using piezoelectric stack actuators is designed to adjust the reference mirror in real-time to solve signal separation between the reference beam and the measuring beam of the miniature Michelson interferometer. The coupling of the 2D angle fine-tuning stage in the x and y directions is analyzed, and the coupling model is established for a relatively precise compensation. Experimental results show that through the proposed 2D angle fine-tuning stage, the measurement range of the probe can be extended to ± $30~\mu \text{m}$ , and the interference signal can still remain stable and uninterrupted.