Piezo Actuator Research Articles

Multifunctional Noncontact Micromanipulation Using Whirling Flow Generated by Vibrating a Single Piezo Actuator.

A noncontact method that can achieve immobilization, transportation, and rotation in the microscale is desired in biological micromanipulation. A multifunctional noncontact micromanipulation method is proposed here based on a vibration-generated whirling flow. Resonance of a cantilever structure is utilized to extend the straight vibration of a single piezo actuator to the 2D circular vibration of a micropipette. The circular vibration in fluids can generate the whirling flow featured with low pressure in the core area and flow velocity gradient. The low pressure can immobilize the objects nearby and transport them together with the micropipette, and the flow velocity gradient is utilized to form a torque to rotate the immobilized object. Experiments of the microbeads are conducted to evaluate the claimed functions and quantify the key parameters that influence the rotation velocity. The cell spheroid is immobilized and rotated for 3D observation, and by assessing the viability of the cells containing in the spheroid, the proposed method is proved noninvasive to living cells. Finally, another important application in operations of mouse egg cells is shown, which indicates that the proposed method is a potential valuable tool in biological micromanipulation.

High-speed AFM imaging via iterative learning-based model predictive control

Atomic force microscopy (AFM) imaging has been broadly used for material topography characterization and observation of dynamic material morphology revolution. However, current efforts on high-speed AFM imaging are still limited. In this study, we propose an iterative learning-based model predictive control (IL-MPC) scheme to achieve high-speed AFM imaging. Integrated with the conventional PI feedback control, the IL-MPC scheme is used in the feedforward path to ensure accurate tracking of the sample topography by the AFM z-axis piezo at high imaging speed. Particularly, IL-MPC combines a model predictive controller (MPC) with an iterative learning controller (ILC), where the MPC ensures the fast convergence of the ILC with the existence of line-to-line sample topography variation and the ILC ensures the precision tracking of the sample topography by dealing with the modeling uncertainty of MPC and the nonlinearities of AFM piezo actuator. Moreover, the proposed IL-MPC can be implemented in time domain so that the computation complexity is greatly reduced compared to other frequency-domain iterative learning feedforward approaches. For validation and demonstration, both the proposed method and the conventional contact-mode AFM are applied to image a silicon calibration sample with square pitches (step height: 178 nm). The experiment results show that the proposed technique can increase the scanning speed to scan rate of 50Hz (with linear tip velocity of 1.7 mm/s) while maintaining the imaging quality.

Piezo-bending actuators for isometric or auxotonic contraction analysis of engineered heart tissue.

Engineered heart tissue (EHT) has proven as valuable tool for disease modelling, drug safety screening, and cardiac repair. Especially in combination with the stem cell technology, these in vitro models of the human heart have generated interest not only of basic cardiovascular researchers but also of regulatory authorities responsible for drug safety. A main limitation of 3D-based assays for evaluating cardiotoxicity is their limited throughput. We integrated piezo-bending actuators in a 24-well system for the generation of strip-like rat and human EHT attached to hollow, elastic silicone posts. Muscle contractions of EHTs induced a measurable electrical current in the piezo-bending actuators that could be analysed for contraction amplitude, frequency, and contraction and relaxation kinetics. Compared with the standard video-optical analysis of contractile activity, the new system allows for (a) the analysis of several tissues in parallel, (b) switching between auxotonic and isometric contractions by inserting a stiff metal post in the silicone post opposing the piezo actuator, (c) continuous measurement over days with low data volume (megabyte), (d) automated measurement without the necessity of adjustment of tissue position for video-optical analysis, (e) reduced complexity and costs, (f) high sensitivity of contraction detection, (g) calculation of absolute contraction force, and (h) suitability for variable tissue geometries. The new set-up for contraction analysis based on piezo-bending actuators is a promising new method for the parallel screening of EHT for pharmacological drug effects and other applications of muscle tissue engineering (e.g., skeletal muscle engineering or cardiac repair).

Interferometric trigger method with dual piezoelectric transducers for digital holographic interferometry

Recently, it has become necessary to detect cracks in structures such as buildings and bridges. Phase-shifting digital holography is one valuable method that can be used to measure the strain distribution on the surface of an object. However, to simplify the optical measurement setup, more compact equipment is required. An interferometric trigger method with dual piezo actuators for phase shifting is proposed. This method is useful for designing a head discrete-type measurement system that uses phase-shifting digital holography with multiple imaging sensors. The ability to phase shift using the proposed trigger method was confirmed with the reconstruction of an object and an experiment that was performed to measure the displacement distribution.

Control of a Piezo Actuator to Adjust the Reflective Surface of the Space-Based Reflector

The task of adjusting and maintaining the shape of the radio-reflective network of a largesized space-based reflector is considered. The possibility of using piezo actuators to solve this problem is estimated. The urgency of the actuator control problem for a wide range of tasks related to the space and aircraft equipment is shown. Different types of control for the chosen mathematical model of a piezo actuator are compared.

Flight envelope expansion based on active mitigation of flutter via a V-stack piezoelectric actuator

The instability of the aircraft’s flexible control surfaces caused by uncontrolled vibrations represents a challenging issue of the aviation security. Flutter is a violent vibration whose amplitude grows strongly in a short time. Once the flutter is reached, the plane is destabilized and it can no longer be controlled. This paper proposes a specially designed demonstrator intended to extend the flight envelope by raising the speed limit at which the flutter occurs. The anti-flutter demonstrator is an intelligent airplane wing model made from a longeron covered by an aerodynamic layer. The wing has an aileron as a primary flight control surface, at one end, and a flange conceived to fix the wing in the aerodynamic tunnel, at the other end. The actuator consists in two V-shaped piezo stacks. The main advantage of the piezo actuator, the bandwidth (about 30 Hz), is exploited. The aero-elastic control is efficient if the deflection of the control surface is of a few degrees while the frequency is of at least 25-30 Hz. The control law is obtained through the receptance method of eigenvalues assignment using the on line input/output measured transfer function rather than the knowledge of system matrices.

Laser Drop on Demand Micro Joining − Analytic Process Model to Quantify Braze Absorptance and Cumulative Energy Balance

Laser drop on demand joining is used for high temperature applications particularly tailored for temperature stable joining of electrode structures of piezo actuators with copper wires. The process is developed, since the generated joints are able to withstand the temperatures occurring during aluminum die‐casting, which is a proposed technology to integrate sensor or actuator functionalities into structural aluminum components. The process is based on melting a spherical copper based braze preform (CuSn12) with a liquidus temperature of 989.85 °C. The preform is induced into a capillary and subsequently molten by a laser pulse. After reaching liquidus temperature, the droplet is ejected from the capillary by inert gas overpressure and wets the surface of the electrode structure and the copper wire, where it results in a firm joint after solidification. In order to be able to estimate the cumulative energy balance during the melting and detachment of the braze material, an analytical model is established in the scope of this work, enabling for the first time to indirectly quantify the braze spheres reflectivity as well as its loss of thermal energy due to convection, radiation, and conduction in situ. The analytic model is verified by experiments. The insights gained, may be applied to investigate other laser based metal joining processes like welding, as it is almost impossible to quantify reflectivity or thermal energy losses directly during the welding process.

Vortex-Driven Rotation for Three-Dimensional Imaging Under Microscopy

The noninvasive rotary motion of bio-objects for three-dimensional (3-D) observation and posture adjustment has been a great challenge in microrobotics. This letter reports a harmless noncontact 360° rotation method with a controllable velocity, which applied the vortex induced by vibrating the micropipette in an open fluidic environment. The micropipette was driven by a piezo actuator, which was mounted on a copper pillar. By generating a resonance between the copper pillar and the piezo actuator fed with sine wave of a specific frequency, we controlled the micropipette to vibrate circularly. The vibration-induced vortex around the micropipette could trap micro objects close to it, and then drive the trapped objects to rotate with the uneven drag force acting on their surface. Experiments of 360° rotation of the microbeads were carried out to demonstrate this method and analyze the rotation velocity. An application in 3-D imaging under optical inverted microscopy was achieved. The spheroids assembled by single cells were rotated, which enabled us to observe the different aspects of the cell spheroids and reconstruct its 3-D view.

On-chip density mixer enhanced by air chamber.

This paper proposes an on-chip density mixer that can achieve even density in a target chamber with a swirling flow enhanced by an air chamber. The system is composed of a main channel, a target chamber where two liquids with different densities are included, an isolated air chamber, and an external vibration pump driven by a piezo actuator at the entrance of the main channel. The air chamber is expected to amplify the vibration owing to structure softening. The amplification would be more pronounced at the resonance frequencies of the structure. We developed the system and conducted experiments. We showed that the swirling motion in the target chamber with an air chamber is stronger than that without an air chamber. We also confirmed that the time resulting in even density is shorter when the pump is driven at a resonance frequency. An air-based virtual valve is introduced for maintaining a constant density in the target chamber.

Improvement in Classification of Tactile Event-Related Potentials using Random-Interval Tasks∗.

The classification accuracy of an event-related potential (ERP) induced by a tactile stimulus is investigated to create a brain-computer interface (BCI). Mechanical tactile stimuli were applied to the left and right index fingers using two piezo actuator probes that were used as a Braille display for the visually impaired. In an experiment, two-class classification was investigated using three kinds of tactile stimulus pattern. The subjects were instructed to pay attention to unusual target stimuli while avoiding other frequent nontarget stimuli. The extracted features were classified using stepwise linear discriminant analysis. As a result, high accuracy was obtained by the task of random intervals compared with the task of constant intervals. It was suggested that the accuracy of the BCI using tactile stimuli is influenced by the concentration on the task.

A low-steering piezo-driven mirror.

We present a piezo-driven translatable mirror with excellent pointing stability, capable of driving at frequencies up to tens of kilohertz. Our system uses a tripod of piezo actuators with independently controllable drive voltages, where the ratios of the individual drive voltages are tuned to minimize residual tilting. Attached to a standard ∅ = 12.7 mm mirror, the system has a resonance-free mechanical bandwidth up to 51 kHz, with displacements up to 2 μm at 8 kHz. The maximum static steering error is 5.5 μrad/μm displaced, and the dynamic steering error is lower than 0.6 μrad μm-1. This simple design should be useful for a large set of optical applications where tilt-free displacements are required, and we demonstrate its application in an ensemble of cold atoms trapped in periodically driven optical lattices.

Development of Very-Low-Temperature Millimeter-Wave Electron-Spin-Resonance Measurement System

We report the development of a millimeter-wave electron-spin-resonance (ESR) measurement system at the University of Fukui using a 3He/4He dilution refrigerator to reach temperatures below 1 K. The system operates in the frequency range of 125–130 GHz, with a homodyne detection. A nuclear-magnetic-resonance (NMR) measurement system was also developed in this system as the extension for millimeter-wave ESR/NMR double magnetic-resonance (DoMR) experiments. Several types of Fabry–Perot-type resonators (FPR) have been developed: A piezo actuator attached to an FPR enables an electric tuning of cavity frequency. A flat mirror of an FPR has been fabricated using a gold thin film aiming for DoMR. ESR signal was measured down to 0.09 K. Results of ESR measurements of an organic radical crystal and phosphorous-doped silicon are presented. The NMR signal from 1H contained in the resonator is also detected successfully as a test for DoMR.

Contact resonance spectroscopy for on-the-machine manufactory monitoring

A piezo resistive, phase locked loop (PLL) controlled micro tactile measurement system for on-the-machine contact resonance spectroscopy (CRS) mapping of square centimetre-sized areas is developed and characterized. The CRS uses the influence of material parameters like the Young’s modulus on the contact stiffness between probing tip and sample surface and thus, the resonance frequency of the in-contact cantilever. Recently, we showed a robust, large-dimension, piezo resistive silicon cantilever (5 mm × 200 μm × 50 μm) with a silicon tip at its free end for tactile probing of high-aspect-ratio geometries and high-speed topography scans (i.e., up to 15 mm/s). For CRS-based layer and material analysis, this cantilever can be excited into resonance by a piezo chip actuator as described in this work. A compact, LabVIEW-controlled, fully automated scanning system using a homemade, μ-controller-implemented software PLL for resonance frequency tracking and out-reading was realized. To verify the measurement principle, analytical modelling was done. Different layer thicknesses of photo resist (PR) on silicon (11 ± 2 nm to 1653 ± 76 nm), point-by-point line scans of material transitions with various Young’s moduli (Si-PR-Si), bulk materials and nano-/micro-structures were investigated to validate the system. For optimization of the sensor sensitivity and efficiency, amplitude and phase were analysed under different conditions (contact force, excitation amplitudes). On-the-machine CRS with tools and work pieces can be a valuable method for quality assurance and reproducibility of future industrial manufacturing and just-in-time production.

Hexapod Hall scanner for high-resolution large area magnetic imaging.

We demonstrate a six-axis scanning imaging apparatus using piezo bending actuators with a large scan range. The six axes of motion of the bending actuators together with the coupling mechanism to the translation stage allow complete control of the sensor position and orientation over the scanning surface, which is ideal for the use of planar sensors such as Hall devices. In particular, the design allows for in situ correction of the probe tilt angle so that the sensor distance to sample surface can be minimized. We investigate the impact of this alignment on the quality of the measured data using an InSb Hall sensor and a magnetic sample. We also demonstrate a synchronous commutation setup that can greatly enhance the magnetic image by reducing the Hall signal offset.

Kinematics of Trunk-Like Robots with Piezo Actuators

This paper presents the investigation of direct and inverse kinematics for piezo robot with spherical joints. Two different actions of spherical piezo actuators are introduced. Several methods to solve inverse kinematics were analyzed. Geometric approach is chosen for solving inverse kinematics because it has a lot of advantages in accordance to other methods. Theory for defining the solution of the inverse kinematics using the global projections of robot links is presented. A concise algorithm using a proposed approach for the solution of the inverse kinematics is shown. DOI: http://dx.doi.org/10.5755/j01.mech.24.2.19205

Cellular in vivo 3D imaging of the cornea by confocal laser scanning microscopy.

We present an in vivo confocal laser scanning microscopy based method for large 3D reconstruction of the cornea on a cellular level with cropped volume sizes up to 266 x 286 x 396 µm3. The microscope objective used is equipped with a piezo actuator for automated, fast and precise closed-loop focal plane control. Furthermore, we present a novel concave surface contact cap, which significantly reduces eye movements by up to 87%, hence increasing the overlapping image area of the whole stack. This increases the cuboid volume of the generated 3D reconstruction significantly. The possibility to generate oblique sections using isotropic volume stacks opens the window to slit lamp microscopy on a cellular level.

Guided ultrasonic waves for detection of debonding in bars partially embedded in grout

This paper deals with theoretical, numerical and experimental investigations of guided wave propagation in multilayered cylindrical bars with pre-existing debonding. The research focuses on a complex description of the nature of the wave phenomena occurring in a debonded specimen with a special emphasis on the influence of the location of damage on the wave conversion and diffraction. Experimental non-destructive and destructive tests are conducted on the laboratory models of ground anchors with a variable debonding length and location. Debonding is simulated by wrapping the bar in the cellophane film with very small thickness, providing indirect contact between steel and grout but reducing grout adhesion to steel. Guided waves are excited and measured at the free end of the bar with the use of piezo actuators. Characteristic reflections are identified in signals registered for anchors with three locations of debonding and five debonding lengths. The obtained results show that despite of such small thickness of debonding (60 µm), guided waves may be used as an effective method for detection of adhesive debonding at an early stage of its development.

Improvements of Piezo-Actuated Stick–Slip Micro-Drives: Modeling and Driving Waveform

Modeling and waveform optimization are important research topics for piezo-actuated stick–slip micro-drives. In this paper, the dynamics of piezo-actuated stick–slip micro-drives (PASSMDs) are theoretically investigated. We introduce an extended model taking the dynamics of the piezo actuators into account. The model combines the whole macroscopic movement of the drive’s runner and actuators and the microscopic behavior of the frictional contacts in a hybrid dynamic simulation. The macroscopic movements are described via Newtonian mechanics, while the microscopic behavior is computed using the method of dimensionality reduction. Two important characteristics of the drive, the critical actuation amplitude and the force generation, are systematically analyzed. The numerical simulation results show a fine agreement with experimental data of the previously published work. The critical actuation amplitude is found to depend on the behavior of the guiding contacts, the dynamics of the actuators and their interaction. Furthermore, a novel driving waveform, which allows us to increase the operational velocity for the drive, is proposed. The waveform is derived by exploiting micro-vibration and considering the dynamic contact status. Simulation results show that the average velocity of the drive is heightened by about 15 % . The performance of the drive is therefore improved.

Stability and vibrations control of a stepped beam using piezoelectric actuation

The objects of this studies are the stability and transversal vibrations of the system composed of three segments, where in the centre part of the system two piezoelectric patches are perfectly bonded to the top and bottom surface of the host beam. The system is kinematically loaded as a result of prescribed displacement of one or both end supports. For the analysis purposes three different beam end supports have been taken into consideration, which prevent longitudinal displacements i.e. clamped-clamped, clamped-pinned and pinned-pinned. This type of beam loading not only affect its natural vibration frequencies but also the system’s stability. By introducing the electric field to the piezo patches, depending on its vector direction, in-plane stretching or compressive residual force may be induced. Presented results show that piezo actuation can significantly modify both the critical buckling force and the vibration frequency.

X-ray beam-shaping via deformable mirrors: surface profile and point spread function computation for Gaussian beams using physical optics.

X-ray mirrors with high focusing performances are commonly used in different sectors of science, such as X-ray astronomy, medical imaging and synchrotron/free-electron laser beamlines. While deformations of the mirror profile may cause degradation of the focus sharpness, a deliberate deformation of the mirror can be made to endow the focus with a desired size and distribution, via piezo actuators. The resulting profile can be characterized with suitable metrology tools and correlated with the expected optical quality via a wavefront propagation code or, sometimes, predicted using geometric optics. In the latter case and for the special class of profile deformations with monotonically increasing derivative, i.e. concave upwards, the point spread function (PSF) can even be predicted analytically. Moreover, under these assumptions, the relation can also be reversed: from the desired PSF the required profile deformation can be computed analytically, avoiding the use of trial-and-error search codes. However, the computation has been so far limited to geometric optics, which entailed some limitations: for example, mirror diffraction effects and the size of the coherent X-ray source were not considered. In this paper, the beam-shaping formalism in the framework of physical optics is reviewed, in the limit of small light wavelengths and in the case of Gaussian intensity wavefronts. Some examples of shaped profiles are also shown, aiming at turning a Gaussian intensity distribution into a top-hat one, and checks of the shaping performances computing the at-wavelength PSF by means of the WISE code are made.