Piezo Actuator Research Articles

External cavity diode laser with frequency drift following natural variation in air pressure.

A compact and mechanically very robust external cavity diode laser was made by removing any position adjusters such as precision screws and piezo actuators, taking advantage of a cat's eye retroreflector insensitive to misalignment. Under free-running operation during 150h, the frequency drift followed natural variation in air pressure with a ratio of -66.6±0.1 MHz/hPa in a range between 1001.5 and 1013.6hPa. The ratio was in good agreement with that estimated from variation in the effective cavity length derived from the relation between the pressure and the refractive index of air. These results indicate that an external cavity diode laser with predictable frequency drift was successfully created.

Effects of hydraulic flow and spray characteristics on diesel combustion in CR direct-injection engine with indirect acting Piezo injector

Recently, the automobile industry has focused on the FIE system of diesel engine with common-rail, EGR, and turbo charger in order to meet a more stringent emission and fuel economy regulations. High-pressure fuel direct injection by using common-rail system is widely accepted because diesel combustion and emission characteristics highly depend on the formation of air-fuel mixture quality. By this fact, an electro-hydraulic injector for common-rail fuel injection system should be designed to have precise and fast response of injector needle’s opening and closing behavior to enhance air-fuel mixing rate. As know, most electro-hydraulic injectors provide its nozzle movement by solenoid coil energy or piezo-actuation. Relatively, servo-hydraulic type piezo injector with bypass-circuit mechanism, which it serve to amplify extension of the piezo stack, is also known for their good efficiency. So the piezo actuator triggers pilot valve for controlling pressure balance, which is accurately regulated by bypass-circuit system. Therefore, main actuation force of piezo injector to move injector needle is hydraulic, which is the key object as it is aimed towards all this research ranges: numerical and experimental approaches. In this study, firstly a full-circuit numerical model of an indirect acting piezo injector with bypass-circuit by using AMESim code has been developed to predict dynamic characteristics of hydraulic components and verified by comparison with experimental data. Also, two experiment schemes were carried out using a constant volume chamber with LED back-illumination system for Mie scattering and a single-cylinder CR direct-injection engine, equipped with a bypass-circuit type piezo and solenoid injector to compare high-speed spray and combustion characteristics in this study because spray penetration and duration are key factor in diesel diffusion combustion. As main results obtained by this study, the injection flow rate and injector internal pressure dynamics calculated by AMESim environment of a bypass type piezo-driven injector reasonably agreed with the experimental result. Also it has better capability in controlling injector needle closing delay and a beneficial effect on diesel diffusion combustion.

Experimental optimization of power-function-shaped drive pulse for stick-slip piezo actuators

Motion of a stick-slip piezo actuator is generally controlled by the parameters related to its mechanical design and characteristics of the driving pulses applied to piezoceramic shear plates. The goal of the proposed optimization method is to find the driving pulse parameters leading to the fastest and the most reliable actuator operation. In the paper the method is tested on a rotary stick-slip piezo actuating system utilized in an atomic force microscope.The optimization is based on the measurement of the actuator response to driving pulses of different shapes and repetition frequencies at various load forces. To provide it, a computer controlled testing system generating the driving pulses, and detecting and recording the corresponding angular motion response of the actuator by a position sensitive photo detector (PSPD) in real time has been developed. To better understand and interpret the experimental results, supportive methods based on a simple analytical model and numerical simulations were used as well.In this way the shapes of the single driving pulses and values of the load force providing the biggest actuator steps were determined. Generally, the maximal steps were achieved for such a combination of the pulse shapes and load forces providing high velocities at the end of the sticking mode of the actuator motion and, at the same time, lower decelerations during the slipping mode.As for the multiple driving pulses, the pulse shapes and values of repetition frequency ensuring the sticking mode of the actuator motion during the pulse rise time together with the maximum average angular rotor velocity were specified. In this way the effective and stable operation conditions of the actuator were provided.In principle, the presented method can be applied for the testing and optimization of any linear or angular stick-slip actuator.

Small-Scale Multiaxial Setup for Damage Detection Into the Very High Cycle Fatigue Regime

Micro electro mechanical systems, coatings, and thin films contain materials that are often subjected to complex loading conditions and high frequencies. Therefore, the implementation of a resonant multiaxial fatigue setup for small-scale samples is of high interest. Finite Element simulations have been used to design small-scale samples which possess very close bending and torsional resonant frequencies. The bending and torsional modes are excited by two piezo actuators working either in or out of phase with one another. The bending and torsional amplitudes are measured independently by a laser and the actuator amplitudes are controlled by a Field Programmable Gate Array. The fatigue setup can be used with a varying range of sample sizes from centimeters down to tens of micrometers. The novel multiaxial resonant micro fatigue setup as well as results (fatigue damage for Ni and lifetime for Cu) from bending small-scale fatigue tests are shown and discussed.

Fibre-coupled multiphoton microscope with adaptive motion compensation.

To address the challenge of sample motion during in vivo imaging, we present a fibre-coupled multiphoton microscope with active axial motion compensation. The position of the sample surface is measured using optical coherence tomography and fed back to a piezo actuator that adjusts the axial location of the objective to compensate for sample motion. We characterise the system's performance and demonstrate that it can compensate for axial sample velocities up to 700 µm/s. Finally we illustrate the impact of motion compensation when imaging multiphoton excited autofluorescence in ex vivo mouse skin.

Experimental investigations into ultrasonic-assisted abrasive flow machining (UAAFM) process

Ultrasonic-assisted abrasive flow machining (UAAFM) process is being investigated as an effective variant of traditional abrasive flow machining process. This process aims to achieve better surface finish at higher finishing rate. In this process, a relatively high frequency (5–20 kHz) is provided to the workpiece externally using a piezo actuator. This additional effect is also termed as ultrasonic assistance. Owing to this, the abrasives present in the medium hit the workpiece asperities mostly at an angle and at a higher resultant velocity, thereby making them more effective. In the present work, experiments were conducted on EN8 steels (AISI 1040) to evaluate the process performance of UAAFM on the double acting horizontal type setup. Response surface methodology (RSM) technique was used for designing the experimental plan with four input parameters—applied frequency, extrusion pressure, abrasive mesh size, and processing time. The results obtained after machining by UAAFM were also compared with traditional AFM process. It was found that significant improvements in surface finish could be recorded in UAAFM. The maximum percentage improvement achieved in surface finish was 81.02 %, while maximum improvement in material removal was 0.05 %. The machined surfaces were also investigated using different characterization tools such as scanning electron microscope (SEM), X-ray diffractometer, and three-dimensional optical profilometer.

Evaluation of the Effect of a Step Change in Piezo Actuator Structure on Vibration Reduction Level in Plates

Abstract This paper presents numerical analyses and a physical experiment on efficiency of different shapes and material composition of piezo actuators on vibration reduction. For this purpose numerical models of a plate clamped on all sides with piezo actuators attached were developed. The elements used were either standard homogeneous elements or the proposed two-part elements with different material composition for inner and outer part of piezo ceramic. Numerical analyses were performed using ANSYS software

Application of Piezofilms for Excitation and Active Damping of Blade Flexural Vibration

Abstract The steam turbine blades of low pressure stages are endangerd by the high-cyclic fatigue due to the combined loading of dynamic stresses by the steam time-variant pressure and the pre-stress from centrifugal forces. Therefore, the importance of their experimental dynamic analysis in the design stage is critical. For laboratory tests of the blades, the piezo actuators placed on the blades, unlike electromagnets placed in the stationary space, give a possibility to excite the flexural vibration of the blades within the bladed disk by time continuous forces independently of the rotor revolutions. In addition, the piezo actuators can be also used to control the vibrations of the blade. Therefore, several dynamic experiments of the clamped model blade equipped with PVDF films were performed for the force description of the piezo foils and their behavior as actuators of the blade vibration. The numerical beam models were used for numerical analysis of the vibration suppression effects both by additional parametric excitation and by active damping. The optimal phase shift of piezo actuator voltage supply was ascertained both for amplitude amplification and suppression. The results contribute to the knowledge of the actuation and active damping of blade vibration by the piezo elements

Investigation of tribological properties of carbide coatings deposited by electrospark at piezoelectric tribocontact

Investigations presented in this paper were carried out using an originally designed rotary piezoelectric motor of a standing wave tribotester. Test conditions, such as the normal force value in the friction pair, the rotor stop torque value, and the test duration can be programmed and changed in a desirable mode. The rotation speed, covered distance and loading torque of a piezo actuator were measured. Two different coatings (WC-Co8 and TiC15-Co6) were tested as the rotor friction surface and the wear of friction pairs (rotor, counter body) was evaluated after the tests. Investigations reveal an incidental advantage of output parameters of the piezo actuator with the TiC15-Co6 coating on the friction pair. Besides, high hardness of carbide surfaces requires paying more attention to the wear resistance of the frictional material of the counter body.

Hybrid mode-locked Er-fiber oscillator with a wide repetition rate stabilization range

We present a hybrid mode-locked Er-fiber oscillator whose repetition rate can be tuned from 101.3 to 103.0 MHz. By incorporating saturable absorption and nonlinear polarization evolution in a ring cavity, mode-locked states can be easily accessed with a 3 dB spectral range wider than 50 nm. In addition, by the combination of a computer-controlled optical delay line and a piezo actuator to change the length of the cavity, the repetition rate can be stabilized at any frequency in the tunable range for the long term. When phase locking to an Rb clock for 14 h continuously, the standard deviation of the fundamental repetition rate is 0.2 mHz with a gate time of 1 s. In addition, the feedback bandwidth can be extended to ∼400 Hz by stabilizing the 10th harmonic instead of the fundamental repetition rate. Furthermore, the linewidth of the comb modes is investigated by beating with a wavelength-tunable diode laser.

Tribological property investigation on a novel pneumatic actuator with integrated piezo actuators

Pneumatic piston–cylinder actuators are commonly used in industry for a variety of automation and robotics applications. In order to suppress leakage, these actuators comprise seal rings which unfortunately introduce friction and affect the positioning accuracy and output force. This article investigates vibrations of the seal generated by integrated piezo actuators to reduce friction force. For this, two piezoelectric stacks are integrated in the cylinder and used to excite vibration modes. This concept was studied in a compact cylinder pneumatic actuator with a bore diameter of 5mm and a stroke of 10mm. Dry friction measurement shows a 52% reduction from the original friction force at a driving frequency of 18.29kHz and vibration amplitude of 0.05μm. In the wet friction experiments, the friction force can be reduced by 54% from the original wet friction with vibrations at amplitude of 0.04μm.

Modelling and investigation of a piezo composite actuator application

This work presents a proposal of modelling and investigation of advanced piezo composite MFC actuator application in one–dimensional flexural vibrating systems. The presented method of analysis of the considered system is based on the discrete–continuous mathematical model and the approximate Galerkin method. Characteristic YV that describes relation between the beam's deflection and applied voltage was calculated. The next step of the work was the analysis of influence of the piezoelectric macro fibre composite's properties on the obtained characteristic of the system. The main aim of this work is to propose a mathematical algorithm of the process of modelling and analysis of systems under consideration that can be very useful in designing process. Obtained results can be used to optimise designed systems for example by selecting geometrical and material parameters of the systems elements including the glue layer between the transducer and mechanical subsystem.

701 振動援用切削による表面微小テクスチャ加工(OS7-(1),OS7 オーガナイズドセッション≪精密/微細加工と評価≫)

The vibration-assisted cutting was performed to fabricate surface microtextures composed of numerous periodical complicated concavo-convex patterns anticipating future usage as the microtexture mold for injection molding. In the experiment, a pure copper plate was machined using a sharply pointed triangular diamond indenter tip vibrated by a piezo actuator in the direction of the cutting depth with μm order amplitude and kHz order frequency. As a result, a textured surface composed of numerous inverted triangular pyramidal impressions surrounded by pileups are successfully fabricated, and their average dimensions are less than 0.3 μm in height and 0.7 μm and 1 μm in pitches in cutting and feed directions, respectively.

Miniature tunable Alvarez lens driven by piezo actuator

Alvarez lenses can achieve focal length tuning by shifting a pair of optical elements with cubic surfaces in a direction perpendicular to the optical axis, offering us a series of advantages including compact structures with large varifocal ranges, ease of packaging, and high stability against external disturbances. In this paper, we present a miniature tunable Alvarez lens driven by a piezo actuator integrated with a compact mechanical displacement amplifier. A flexure-guided structure with a displacement amplification ratio of ∼16 is adopted in the mechanical design and a novel method to determine surface profile coefficients in the optical design is employed to optimise the lens performance. Results show that the displacement vs. voltage curve of the mechanical displacement amplifier is nearly linear. A maximum displacement of ∼100 μm is obtained with a 130 V input voltage applied to the piezo actuator. Dynamic tuning of focal length about 2.3 times (from 28 mm to 65 mm) is experimentally demonstrated with the assembled Alvarez lens. Images of a USAF 1951 resolution target through the lens at different focal lengths are captured by a high-resolution camera to evaluate the lens performance. No obvious distortion or blurring of images or performance degradation while tuning are noticed within the whole varifocal range.

Speckle reduction for a laser light sectioning sensor

Automated optical inspection is an important test procedure in electronic circuits assembly. Frequently 3d information is required and laser light sectioning sensors are often applied. However, some effects complicate the reliable automatic detection of the shape of such assemblies and their components. The packages of electronic components often are made of black plastics or ceramics so that the intensity available for the optical detection is quite low, especially in comparison to the surface of the PCBs where the components are mounted on. In addition due to rough surfaces of the components and the coherence length of the laser light speckle structures arise. In the work presented here a piezo actuator is used to oscillate the illuminating laser lines along the direction of the lines. The aim is to reduce the visibility of the speckle structures by averaging while maintaining the geometrical shape of the lines. In addition, image processing methods like segmentation and skeletonization are used to allow the detection of the shape of components and assemblies also if materials with distinct differences in the reflectivity are involved. Investigations include the influence of the parameters amplitude and frequency of the piezo actuator.

Data-based and analytic modelling for model-based control of a flexible beam

This paper evaluates and compares data-based and analytic modelling for model- based active vibration control based on the performance of the closed loop system for a simply supported flexible beam. The thin beam is controlled utilizing collocated piezo patch actuators and sensors. An electrodynamic shaker introduces a disturbance force in the direction of oscillation. The data-based design plant is identified using N4SID. The analytically obtained design plant is based on a one-dimensional finite element (FE) model. The comparison of the two entirely different modelling approaches is validated using a variety of different optimal & robust multi-input multi-output (MIMO) control design methods.

エネルギー回生式セミアクティブ振動制御装置に対するSRS制約を導入した圧電アクチュエータ最適配置

Vibration suppression is one of the most important problems in the design and operation of space structures. Due to limited launch capabilities, such structures need to be extremely light-weight although some structures succumb to vibrations because of their low structural stiffness. Moreover, vibrational energy is hard to disperse in the vacuum of space, in contrast to ground environments. These problems can be overcome by vibration control schemes.Vibration control schemes can be categorized into three types: active, passive and semi-active. The semi-active vibration control (SAVC), dynamically changes some property of the structure according to feedback from the state, without adding extra energy. SAVC systems are usually able to achieve higher performance than the passive vibration control schemes without the disadvantages of the active vibration control systems. In this study, optimal piezo actuator layout is solved by the introduction of Shock Response Spectrum (SRS) constraint which evaluates vibration and a shock.

Single-cell printing based on impedance detection.

Label-free isolation of single cells is essential for the growing field of single-cell analysis. Here, we present a device which prints single living cells encapsulated in free-flying picoliter droplets. It combines inkjet printing and impedance flow cytometry. Droplet volume can be controlled in the range of 500 pl-800 pl by piezo actuator displacement. Two sets of parallel facing electrodes in a 50 μm × 55 μm channel are applied to measure the presence and velocity of a single cell in real-time. Polystyrene beads with <5% variation in diameter generated signal variations of 12%-17% coefficients of variation. Single bead efficiency (i.e., printing events with single beads vs. total number of printing events) was 73% ± 11% at a throughput of approximately 9 events/min. Viability of printed HeLa cells and human primary fibroblasts was demonstrated by culturing cells for at least eight days.

Penetration Force in Biopsy under Condition of Biomimetic Vibration

Biopsy is a common medical procedure to treat and diagnose prostate cancer and breast cancer. Needle insertion is a critical step in biopsy, but the inserting force has a big effect on precision of needle insertion. A new method is presented to reduce the penetration force, and then improve the precision of needle insertion in this paper. Preloaded piezo actuator was introduced to provide biomimetic vibration for needle during needle insertion into a pork liver, just as a fascicle insertion into the skin by a mosquito. The experimental results showed that the penetration force was reduced 26.7% compared with the force without biomimetic vibration.

Simulation of media behaviour in vibration assisted abrasive flow machining

Abrasive flow machining (AFM) is an abrasive-based precision finishing process used for achieving surface finish in micro and nano-level. The AFM polishes surfaces by extruding a visco-elastic media in contact with the workpiece. The media, also called a ‘flexible tool’, plays a key role in the performance of the process. Ultrasonic assisted abrasive flow machining (UAAFM) is a new variant of the AFM process in which the workpiece is subjected to mechanical vibration orthogonal to the media flow direction. In this process a high frequency, in the range of about 5–20kHz, is given to the workpiece with the help of a piezo actuator and a specially designed fixture. The present work highlights on the possible behaviour of the tool (media) during UAAFM and its effect on the machining process through a computation based approach. Commercially available simulation tool was used to study the effect of the media in response to different set of machining conditions. The responses were evaluated in terms of changes in the fluid pressure, velocity profile of the fluid, temperature distribution in the working fluid and the possible wall shear on the work surface. A three-dimensional model was constructed for simulating the UAAFM process. The simulation shows that the abrasive particles tend to hit the target surface at an angle ‘θ’ which significantly affects the basic mechanisms involved and enhances the effectiveness of the process. The computed wall shear explains that the process will have higher finishing rate and hence the performance. The enhanced interaction of abrasive media in UAAFM while compared to simple AFM could be explained by the resultant pressure–velocity phenomena. Results show that while changes in the amplitude of applied vibration (10μm and 50μm) significantly affect the wall shear, the media velocity and pressure profiles are only marginally sensitive to this parameter. The simulation results also confirm that the rise in temperature during the process will not affect the media stability. Results have been discussed vis-a-vis the basic mechanism of the process through suitable illustrations.