Actuators, Piezoelectric Ceramic, Functional Gradient

With the development of modern science and technology, many high technology fields have entered the nano-world, such as processing and manufacturing of aerospace products, precision measurement devices, and high density integrated circuits and so on. Close to the nanometer scale with the characteristic size of atoms and molecules, the general conventional techniques are no longer applicable, and therefore many countries focused their eyes on the study of nanotechnology, especially in nano-operation and measurement techniques. Piezoelectric ceramic actuator driver for its excellent performance is widely used in micro/nano positioning operation fields. However, due to the existence of its own hysteresis, creep and nonlinear shortcomings seriously affect the accuracy of the nano-scale position. To solve the above problem, we designed a displacement sensor to measure the real-time displacement of piezoelectric ceramic actuator and use the close-loop control which based on the feedback of displacement to improve the positioning accuracy of piezoelectric ceramic actuator driver. After the improvement, the nano-displacement sensor's accuracy has reached the nanometer level. Experimental results show that the resarch in this paper can really improve the performance of the nanodisplacement sensor.

With the development of modern science and technology, many high technology fields have entered the nano-world, such as processing and manufacturing of aerospace products, precision measurement devices, and high-density integrated circuits and so on. Close to the nanometer scale with the characteristic size of atoms and molecules, the general conventional techniques are no longer applicable, and therefore many countries focused their eyes on the study of nanotechnology, especially in nano-operation and measurement techniques. Piezoelectric ceramic actuator driver for its excellent performance is widely used in micro/nano positioning operation fields. However, due to the existence of its own hysteresis, creep and nonlinear shortcomings seriously affect the accuracy of the nano-scale position. To solve the above problem, we designed a displacement sensor to measure the real-time displacement of piezoelectric ceramic actuator and use the close-loop control which based on the feedback of displacement to improve the positioning accuracy of piezoelectric ceramic actuator driver. After the improvement, the nano-displacement sensor's accuracy has reached the nanometer level. Experimental results show that the research in this paper can really improve the performance of the nano-displacement sensor.

The basic operation principle of elastic support/dry friction damper in rotor system was introduced and the unbalance response of the rotor with elastic support/dry friction damper was analyzed theoretically. Based on the previous structure using an electromagnet as actuator, an active elastic support/dry friction damper using piezoelectric ceramic actuator was designed and its effectiveness of reducing rotor vibration when rotor traverses its critical speed and blade-out event happened was experimentally verified. The experimental results show that the active elastic support/dry friction damper with piezoelectric ceramic actuator can significantly reduce vibration in rotor system; the vibration amplitude of the rotor in critical speed region decreased more than 2 times, and the active damper can protect the rotor when a blade-out event happened, so the rotor can traverse the critical speed and shut down smoothly. In addition, the structure is much simpler than the previous, the weight was reduced by half and the power consumption was only 5 W.

By appropriate superposition of two standing waves a traveling wave can be excited in the ring-shaped stator of a traveling wave motor. Thus the material points on the surface of the stator perform an elliptical motion. A second disk, pressed against the stator, is driven by frictional forces, generated in the interface between stator and rotor. Traveling wave motors produce a very high torque at low rotational speed. Their simple mechanical design and good controllability make these motors a very promising alternative to small electro-magnetic motors. The mechanical oscillations of high frequency are excited by piezoelectric ceramic actuators, bonded to the surface of the stator. The dynamic behavior of the stator is strongly influenced by these actuators. Since it is very difficult to produce big ceramic rings for large stators and bond them to the stators we tried to excite a large stator using single piezoelectric elements. The geometry of the ceramic actuators as well as the stiffness of the bonding layer do have marked influence on the efficiency of the excitation, because the actuation mechanism is of induced strain type and the stator is excited by tangential stresses in the bonding layer. In this paper the influence of the shape of the ceramics on the vibration of the stator is investigated using the finite element method. A detailed model taking into account the piezoelectric effect in the ceramic actuators as well as the exact geometry of the stator is used to calculate the transfer function between the electrical excitation and the mechanical vibrations of the stator. The results allow one to compare the efficiency of different actuator configurations.

By appropriate superposition of two standing waves, a traveling wave can be excited in the ring-shaped stator of a traveling wave motor. Thus, the material points on the surface of the stator perform an elliptical motion. A second disk, pressed against the stator, is driven by frictional forces, generated in the interface between stator and rotor. Traveling wave motors produce a very high torque at low rotational speed. Their simple mechanical design and good controllability make these motors a very promising alternative to small electromagnetic motors. The mechanical oscillations of high frequency are excited by piezoelectric ceramic actuators, bonded to the surface of the stator. The dynamic behavior of the stator is strongly influenced by these actuators. Since it is difficult to produce big ceramic rings and bond them to the stators, single piezoelectric elements have to be used for the excitation of large stators. The geometry of the ceramic actuators as well as the stiffness of the bonding layer do have marked influence on the efficiency of the excitation, because the actuation mechanism is of induced strain type and the stator is excited by tangential stresses in the bonding layer. In this paper, the influence of the shape of the ceramics on the vibration of the stator is investigated using the finite element method. A detailed model taking into account the piezoelectric effect in the ceramic actuators as well as the exact geometry of the stator is used to calculate the transfer function between the electrical excitation and the mechanical vibrations of the stator. The results allow to compare the efficiency of different actuator configurations.

In order to characterize the hysteretic characteristics between the output displacement andapplied voltage of pre-stressed piezoelectric ceramic stack actuators (PCSAs), this paperconsiders that a linear force and a hysteretic force will be generated by a linearextension and a hysteretic extension, respectively, due to the applied voltage to apre-stressed PCSA and the total force will result in the forced vibration of thesingle-degree-of-freedom (DOF) system composed of the mass of the pre-stressed PCSAand the equivalent spring and damper of the pre-stressed mechanism, which lets the PCSAbe pre-stressed to endure enough tension. On this basis, the phenomenological modelto characterize the hysteretic behavior of the pre-stressed PCSA is put forwardby using the Bouc–Wen hysteresis operator to model the hysteretic extension.The parameter identification method in a least-squares sense is established byidentifying the parameters for the linear and hysteretic components separatelywith the step and periodic responses of the pre-stressed PCSA, respectively. Theperformance of the proposed phenomenological model with the corresponding parameteridentification method is experimentally verified by the established experimental set-up.The research results show that the phenomenological model for the pre-stressedPCSA with the corresponding parameter identification method can accuratelyportray the hysteretic characteristics of the pre-stressed PCSA. In addition, thephenomenological model for PCSAs can be deduced from the phenomenological model forpre-stressed PCSAs by removing the terms related to the pre-stressed mechanisms.

9 - Metal-ceramic functionally graded materials (FGMs)

The actuator is a critical component of the micromanipulator. By utilizing the properties of expansion and contraction, the piezoelectric actuator enables the manipulator to handle and grasp miniature objects during micromanipulation. However, in piezoelectric ceramic disc actuators with conventional surface electrode configurations, the actuating force generated in the radial direction is relatively limited. When used as the actuation element of the manipulator, achieving regulation over a wide range of operating strokes becomes challenging. Therefore, altering the electrode structure is necessary to generate a greater radial force, thus enhancing the positioning and grasping capabilities of the operating arm. This paper investigates a piezoelectric actuator with interdigitated spiral electrodes, featuring a constant pitch between adjacent electrodes. The radial force was tested under mechanical clamping conditions, and the influence of the electrical signal was examined. The characteristics of the electrode structure were described, and the working principles of the piezoelectric actuators were analyzed. Theoretical equations were derived for the macroscopic characterization of the radial clamping force of the actuator, based on the piezoelectric constitutive equation, geometric principles, and Bond matrix transformation relationships. A finite element model was developed, reflecting the features of the electrode structure, and finite element simulations were employed to verify the theoretical equations for radial force. To prepare the samples, encircled interdigitated spiral electrode lines were printed on the PZT-52 piezoelectric ceramic disc using a screen printing method. The clamping force experimental platform was established, and experiments on the clamping radial force were conducted with electrical signals of varying waveforms, frequencies, and voltages. The experimental results show that the piezoelectric ceramic disc actuator with an interdigitated spiral electrode line structure, when excited by a stable sine wave operating at 200 V and 0.2 Hz, generated a peak force of 0.37 N. It was 1.76 times greater than that produced by a previously utilized piezoelectric disc with conventional electrode structures.

The use of the fast steering mirror in an optical path requires strict volume control, and traditional structures have low space-utilization efficiency, resulting in traditional actuators having limited output in narrow spaces. The design in this paper adopts a combination of flexible universal supports and piezoelectric ceramic actuators, greatly reducing the layout space of the rotating-shaft system. We accurately model the design structure and develop closed-loop control methods to further improve the closed-loop control accuracy of the system. The experimental results indicate that the developed control method effectively improves the response speed and bandwidth and thus has good potential for use in engineering applications.

Piezoelectric and Electrostrictive Ceramics Transducers and Actuators

Piezoelectric and Electrostrictive Ceramics Transducers and Actuators

A set of measurements is presented, characterizing a particular piezoelectric ceramic multilayer actuator type up to an electric field strength of 10 V/μm. The relation between strain and dielectric displacement remains linear and shows low hysteresis up to 4 V/μm. Only at the highest field strengths nonlinear behaviour is observed. Room temperature and 150 °C poling are compared. Room temperature poling results in lower charge constants and a larger amount of depoling. The effect of poling temperature can be explained by a mechanical alignment of the inactive ceramic material. By this mechanism the high temperature poled actuator ends up in a macroscopically stress free state. The residual stresses at room temperature poling cause the observed lower charge constant and larger amount of depoling.

Ceramic-metal functionally graded materials (FGMs) are advantageous to two dissimilar materials joined directly together, which includes smoothing of thermal stress distributions, minimization or elimination of stress concentrations and singularities at the interface corners and increase in bonding strength. In this study, ZrO2/ 304 stainless steel (SUS304) FGMs with continuous gradient manners, not stepwise manners, were fabricated by a combination of centrifugal slurry methods and spark plasma sintering (SPS). The size and surface smoothness of the powders of SUS304 highly affected formation of compositional gradient patterns in the FGMs. Effects of ball milling time and ball sizes on such conditions of the powders as well as compositional gradients in the FGMs were investigated by microstructure observations with element analysis and hardness probing on the cross sections of the FGMs.

Four-component barium titanate stannate (BaTi1−x Sn x O3, BTS) functionally graded materials (FGMs) were designed, processed and examined. BTS powders with different tin content (x = 0.025, 0.05, 0.07 and 0.10, abbreviated as BTS2.5, BTS5, BTS7 and BTS10, respectively) were used as ingredient materials. Four-layered samples, produced by powder-stacking method and uniaxial pressing, were consolidated in BTS2.5/BTS5/BTS7/BTS10 FGMs by sintering at 1420 °C with dwell time of 2 h. To achieve high-quality FGMs, without structural or microstructural damages, the master sintering curve (MSC) approach were used. In this study, the MSC was constructed for four-layered FGMs using shrinkage data obtained by a heating microscope during non-isothermal part of the sintering up to 1420 °C with heating rates of 2, 5, 10 and 30°/min. To prepare FGMs with desired final density the corresponding Θ value was estimated from the abscissa of the master sintering curve. Estimated Θ value was used in Φ(ρ) = logΘ(t,T(t)) equation, which correlate density (ρ) and the time and temperature dependent parameter Θ(t,T(t)). This calculation allowed us to determine experimental parameters which should be applied in sintering procedure to obtain FGMs with projected density. According to constructed MSC, four different sintering schedules were designed and applied where four BTS2.5/BTS5/BTS7/BTS10 FGMs were prepared. To validate the constructed MSC, the microstructure and chemical (Ti/Sn) gradient in the prepared FGMs were examined by SEM–EDS methods.

Destruction mechanisms were investigated in electrostrictor, piezoelectric and phase-change antiferroelectric ceramic multilayer actuators with an interdigital electrode configuration. Simultaneous observations were done by three different methods; visual observation with a charge coupled device (CCD) microscope, field-induced strain and acoustic emission (AE) measurements. During a cyclic electric field application, the crack was initiated from the edge of an internal electrode and propagated obliquely to another electrode in the piezoelectric sample, while in the antiferroelectric, the crack was initiated between a pair of electrodes and propagated parallel to the electrodes. The field-induced strain curve exhibited asymmetric and enhanced strains in all the samples during the crack propagation, probably due to the internal delaminations. The AE count also increased drastically before the destruction.