A parasitic type piezoelectric actuator with an asymmetrical flexure hinge mechanism

A parasitic type actuator with an asymmetrical flexure hinge mechanism has been proposed in this study to achieve linear motion with a large working stroke. The principal output direction of the piezoelectric stack is vertical to the motion direction of the mover to obtain a large output load. The composition of the parasitic type actuator and working process are introduced and parasitic motion is explained. Finite element method has been applied to analyze the parasitic motion of the proposed asymmetrical flexure hinge mechanism. Moreover, an experiment system of the parasitic type actuator is set up, and experiments show that the positioning resolution of the actuator is around 0.1 μm; the maximum motion speed could achieve to 2850 μm/s when the input frequency f = 500 Hz and the input voltage U_e = 100 V; the maximum output force F_g is up to 750 g when the input frequency f = 1 Hz and the input voltage U_e = 100 V. This study indicates that the asymmetrical flexure hinge mechanism could achieve parasitic motion for the design and application of piezoelectric actuators with a large working stroke.

     

An experimental and numerical investigation into the effects of the PZT actuator shape in polymethylmethacrylate (PMMA) peristaltic micropumps

Utilizing a solvent-assisted bonding process, two diffuser-type polymethylmethacrylate (PMMA) peristaltic micropumps are fabricated with a linear array of circular microchambers with a depth and diameter of 15 m and 7 mm, respectively, actuated using either square or circular PZT actuators. Experimental trials are performed to characterize the performance of the two micropumps under driving frequencies ranging from 80 to 150 Vpp and actuation frequencies in the range of 10 Hz to 1 kHz. The results reveal that the micropump with square PZT actuators generates a maximum pumping rate and back pressure of 217 l/min and 9.2 kPa, respectively, while the micropump with circular actuators generates a maximum flow rate of 131 l/min and a back pressure of 2.7 kPa. ANSYS finite element simulations demonstrate two events. First, given an equivalent surface area, the circular actuators undergo a greater displacement than the square actuators under given actuation conditions. In other words, the circular actuator design is more efficient to represent a higher ratio of the displacement to the actuation area (d/A). However, the circular actuators with the surface area of 38.47 mm² are smaller than the square actuators (49 mm²). In addition, it is inferred that the relatively poorer performance of the circular actuators is due in part to thermal damage of the PZT patches during their removal from the bulk PZT chip using a laser cutting device in the pump fabrication process. Secondly, when the shape of the effective working area for the actuation is rectangular which is usual in a MEMS design, the rectangular actuator with length of 7 mm has significantly higher displacement (0.71 m) than that of the circular actuator with diameter of 7 mm (0.396 m). Consequently, a rectangular actuator design presents a more practical solution for higher performance of micro-actuators.     

Fringing capacitance and tolerance of DRIE effect on the performance of bulk silicon comb-drive actuator

A bulk silicon comb-drive actuator with low driving voltage and large displacement is presented in this paper. The bulk silicon comb-drive actuator is fabricated by a simple bulk micromachining process based on the low temperature Au–Au bonding technology. A cascade folded beam is designed to improve the displacement of comb-drive actuator at low driving voltages. The instability of the whole system decreases by utilizing unequal wide comb fingers design. The fringing capacitance and the fabrication tolerances together with their effects on the performances of the comb-drive actuators are also discussed. The measurement results show that the capacitance change rate and the displacement change rate of the comb-drive actuator are 1.5 fF/V² and 0.125 μm/V², respectively. The displacement of the actuator can reach 28.5 μm at 15 V driving voltages. The experimental results of the comb-drive actuator are in good agreement with the modified theoretical predictions.

     

Effect of electrode size and silicon residue on piezoelectric thin-film membrane actuators

Piezoelectric micro-electromechanical systems (MEMS) often adopt a membrane structure to facilitate sensing or actuation. Design parameters, such as membrane size, thickness of the piezoelectric thin film, and electrode types, have been studied to maximize actuation, sensitivity, or coupling coefficient. This paper is to demonstrate numerically and experimentally that the size of silicon residue and its relative size to the top electrode are two critical yet unrecognized parameters in maximizing the actuation displacement of PZT thin-film membrane actuators. To study effects of the silicon residue, we have developed a finite element model using ANSYS. The model consists of five components: a square passive silicon membrane, a silicon substrate, a PZT thin film, a square top electrode, and a silicon residue region. In particular, the silicon residue has a circular inner diameter and a square outer perimeter with a trapezoidal cross section. Predictions of the finite element model lead to several major results. First, when the silicon residue is present, there exists an optimal size of the top electrode maximizing the actuator displacement. Second, the optimal electrode size is roughly 50–60% of the inner diameters of the silicon residue. The displacement of the membrane actuator declines significantly as the electrode overlaps with the silicon residue. Third, the maximal actuator displacement decreases as the inner diameter of the silicon residue decreases. Aside from the finite element analysis, a mechanics-of-material model is also developed to predict the electrode size that maximizes the actuator displacement. To verify the simulation results, eight PZT thin-film membrane actuators with progressive electrode sizes are fabricated. These actuators all have a square membrane of 800 μm × 800 μm with the inner diameter of the silicon residue controlled between 500 and 750 μm. A laser Doppler vibrometer is used to measure the actuator displacements. The experimental measurements confirm that there exists an optimal size of the top electrode maximizing the actuator displacement.     

Design and testing of a microgripper with SMA actuator for manipulation of micro components

The extremely high work-to-volume ratios of the SMA actuators make them suitable to be used as a powerful actuator in micro-scale manipulation. In this study, an easily manufacturable micro-gripper with shape memory alloy (SMA) wire actuator was designed and manufactured. The concept of the designed micro-gripper was based on flexible hinge structures to increase the deflection efficiency and strength. The size of microgripper was a significant criterion in our design. Also, innovative layout in locating of SMA wire caused the microgripper to gripe and manipulate a boarder range of objects. The finite element method was used to analyze and calculate the stress distribution and jaw’s deflection in the gripper. In order to verify the modeling results, an experimental analysis by building a set-up for micro-gripper and running tests were implemented and it showed a good agreement with the modeling results. The approximate size of the micro-gripper is about 12 × 10 mm and its maximum achievable deflection is 200 μm which is perceptibly higher than SMA actuated micro-grippers with the same size.

     

Displacement amplifier for piezoelectric actuator based on honeycomb link mechanism

This study proposes a compact and array-type design of a mechanical amplifier for piezoelectric actuators. The amplifier emulates in-plane deformation of a specific honeycomb having bow-tie-type reentrant cells. When a multilayer piezoelectric actuator causes the elongation of a cell of the amplifier in the longitudinal direction, the cell causes expansion in the transverse direction with amplification depending on its geometry. For ease of fabrication of the amplifier, a plate having periodic patterns of two holes and a slit is proposed, in which all walls and corners of the cell are replaced with rigid links and elastic hinges, respectively. Compactness of an amplified piezoelectric actuator based on the honeycomb link mechanism is demonstrated by using prototypes of uniaxial actuators and XY stages. Furthermore, theoretical formulas are discussed, which are used in the design of the amplified actuators.     

On piezoelectric super-helix actuators

Theoretical designs of piezoelectric ceramic helical and spiral actuators have existed for many years. The main reason these devices have not achieved widespread recognition and use is the perceived difficulty of processing such forms. These processing problems, covering both the material form itself and electrode placement, have been tackled and solved over recent years at the University of Birmingham. A new type of complex piezoelectric spring-type actuator has arisen as a result of this work, which takes the form of a super-helix, and is known as a wound helical electrically reactive mechanism (WHERM). This actuator structure shows a great deal of versatility in terms of the device parameters, which can be tailored to suitable applications. We show here that the geometry of this actuator effectively provides for an efficient method of amplifying the small strain produced in a piezoelectric material in exchange for a proportional reduction in maximum force holding ability. Devices shown exhibit peak no-load displacements of over ±3 mm, with a force holding ability of up to 0.2 N, and with a total circular footprint of less than 45 mm in diameter.     

Synthesis and performance evaluation of thin film PPy-PVDF multilayer electroactive polymer actuators

Bending-type microactuators less than 1 mm in length and comprising of two polypyrrole (PPy) layers separated by polyvinylidene fluoride (PVDF) membrane have previously been fabricated and was shown to operate both in air and aqueous media. The main limiting factor to increase the bending angle and to further miniaturise these actuators was the thickness of the commercially-available PVDF membrane used (～110 μm). In this study, we have synthesised a porous PVDF thin film with a thickness of 32 μm using a spin coating technique, and electrochemically deposited PPy layers on both sides of this thin film to make ultra thin film polymer actuators. The electromechanical and electrochemical properties are investigated and compared with those of the thicker actuator system using the commercially-available PVDF and under identical conditions. The thin film shows very promising performance compared to its thicker counterpart.     

Application of piezoelectric layers in electrostatic MEM actuators: controlling of pull-in voltage

In this paper, a novel method has been developed to control the pull-in voltage of the fixed-fixed and cantilever MEM actuators and measure the residual stress in the fixed-fixed model using of the piezoelectric layers that have been located on the upper and lower surfaces of actuator. In the developed model, the tensile or compressive residual stresses, fringing-field and axial stress effects in the fixed-fixed end type micro-electro-mechanical systems actuator have been considered. The non-linear governing differential equations of the MEM actuators have been derived by considering the piezoelectric layers and mentioned effects. The results show that due to different applied voltage to the piezoelectric layers, the pull-in voltage can be controlled and in the fixed-fixed type the unknown value of the residual stress can be obtained.     

A microgripper using piezoelectric actuation for micro-object manipulation

Design, fabrication and tests of a monolithic compliant-flexure-based microgripper were performed. The geometry design and the material stresses were considered through the finite element analysis. The simulation model was used to study in detail profiles of von Mises stresses and deformation. The maximum stress in the microgripper is much smaller than the critical stress values for fatigue. The microgripper prototype was manufactured using micro-wire electrode discharge machining. A displacement amplification of 3.0 and a maximum stroke of 170 μm were achieved. The use of piezoelectric actuation allowed fine positioning. Micromanipulation tests were conducted to confirm potential applications of the microgripper with piezoelectric actuation in handling micro-objects. The simulation and experimental results have proven the good performance of the microgripper.     

Demonstration of optimizing piezoelectric polarization in the design of a flextensional actuator

Much effort has gone into amplifying the displacements of actuators built around piezoelectric materials (PZTs). Some researchers have used topology optimization to design compliant mechanisms that best magnify either the geometric or mechanical advantage of piezoelectric wafers or “stack” actuators. PZTs are generally poled through the “thin” direction, so actuation by an electric field in that direction only induces eigenstrains normal to the free edges. Some researchers have shown advantages of “shear mode” actuation, and material scientists have demonstrated the ability to pole a PZT in an arbitrary direction. This work attempts to justify the inclusion of the PZT polarization vector as a design variable in the design of a flextensional actuator. We present two examples based on the “cymbal” actuator: one using a simplified model to justify off-angle polarization and another using the polarization vector as a design variable to optimize the topology of a compliant mechanism.     

大位移压电陶瓷驱动器的有限元分析

为研究压电陶瓷驱动器的驱动效能,制作了大位移压电陶瓷驱动器.基于压电陶瓷材料的机电耦合特性,应用动力学有限元分析方法,将大位移压电陶瓷驱动器离散成一系列四面体单元,分别进行了力学和电学分析.根据压电陶瓷的基本压电方程,耦合了位移模式与电场模式的有限元模型,建立了压电陶瓷驱动器的有限元动力学模性.利用有限元分析软件ANSYS中的直接耦合场进行分析求解,分析结果与试验测量值取得了良好的一致,证实了利用压电陶瓷双晶片弯曲变形,制作的大位移压电陶瓷驱动器结构设计的合理性.该分析方法对压电陶瓷驱动器的设计、制造与测试具有理论指导意义.     

Thin-Film PZT Lateral Actuators With Extended Stroke

Many microelectromechanical system applications require large in-plane actuation forces, with stroke lengths ranging from submicrometer to tens of micrometers in distance. Piezoelectric thin films are capable of generating very large actuation forces, but their motion is not easily directed into lateral displacement in microscale devices. A new piezoelectric thin-film actuator that uses a combination of piezoelectric unimorph beams to generate lateral displacement has been developed. The piezoelectric actuators were fabricated using chemical-solution-derived lead zirconate titanate thin films. These actuators have demonstrated forces greater than 7 mN at displacements of nearly 1 $muhbox{m}$, with maximum stroke lengths at 20 V greater than 5 $muhbox{m}$ in a 500- $muhbox{m}$-long by 100-$mu hbox{m}$-wide actuator. Force and displacement capabilities can be manipulated through simple changes to the actuator design, while actuator nonlinearity can produce dramatic gains in work capacity and stroke length for longer actuators.$hfill$[2007-0298]      

Characterization and modeling of the dynamic behavior of a liquid–vapor phase change actuator

The dynamic behavior of a liquid–vapor phase change actuator has been investigated. A modular liquid–vapor phase change actuator was designed and fabricated. The actuator consists of a cavity filled with a two-phase fluid bounded on the bottom by a thin membrane into which heat is added and on the top by a cover slip which is displaced by the expansion of the vapor. A parametric study of geometric and operation parameters was conducted. A lumped parameter mathematical model of the actuator was developed to predict the dynamic behavior of the actuator. The model was validated against measured data. Based on the parameter study, actuators with smaller bubbles experienced higher heat loss. Thicker actuators were associated with higher thermal inertia. Thermal inertia, as well as heat losses, had a major effect on the dynamic behavior of the actuator. The model showed that faster response times and higher sensitivity can be achieved if the thermal inertia and heat loss coefficient values are reduced. Time constants less than 2.5 ms and displacement sensitivity higher than 30 μm/W are feasible.     

Analysis of a 0.1-μm stepping bi-axis piezoelectric stage using a 2-DOF lumped model

Piezoelectric stages are widely used for parts manipulation, including micro-component assembly and bio-cell manipulation. This paper proposes a bi-axis piezoelectric stage based on a friction driven mechanism. The carrier slides on a supporting frame and slider constructed in the same plane as a low-profile stage. The dynamic model of the friction driven is based on a 2-DOF lumped model considering the impact and separation behavior. The first mass is the bulk piezoelectric actuator (slab)—as a vibrator—and the second is the driven slider. The stiffness ratio of the piezoelectric slab-to-the driven slider affects the output force of the slider because of the contact time ratio. Moreover, the stepping size is adjusted according to the duty ratio of the pulse width of the driving signal. The stepping size of 0.1 μm is achieved in the X and Y axes corresponding to 3% and 5% of the duty ratio, respectively, of 512-Hz carrier frequency in 20-Vpp driving signal. When the duty ratio is 100%, the full speed of 18 and 16 mm/s are achieved in the X- and Y-axes, respectively. The dimensions of the piezoelectric stage are 61 × 58 × 21.3 (high) mm³.

     

The monolithic integration system of bulk-Si sensors and actuators based on the Au–Au bonding technology

The monolithic integration of bulk-Si MEMS sensors and actuators using the Au–Au bonding technology is presented in this work. With this technology, the substrate isolation and electrical interconnection between the CMOS circuits and bulk-Si CMOS MEMS sensors are achieved perfectly. In order to demonstrate this technology, a pressure sensor and an electrothermal actuator have been monolithically designed and fabricated. In addition, by sputtering aluminium on the bulk silicon electrothermal actuator, the electrothermal actuator is modified and the sensitivity of the actuator is obviously improved. The measurement results show that the sensitivity of the pressure sensor is 0.29fF/hPa. And the sensitivities of the modified and non-modified electrothermal actuators are 20.23 μm/V and 3.34 μm/V, respectively. Compared with the non-modified electrothermal actuators, the sensitivity of the modified electrothermal actuators is improved by 6 times.     

Tolerance analysis for comb-drive actuator using DRIE fabrication

Deep reactive ion etching (DRIE) process is specially invented for bulk micromachining fabrication with the objective of realizing high aspect ratio microstructures. However, various tolerances, such as slanted etched profile, uneven deep beams and undercut, cannot be avoided during the fabrication process. In this paper, the origins of various fabrication tolerances together with its effects on the performances of lateral comb-drive actuator, in terms of electrostatic force, mechanical stiffness, stability and displacement, are discussed. It shows that comb finger with positive slope generates larger electrostatic force. The mechanical stiffness along lateral direction increases when the folded beam slants negatively. The displacement is 4.832 times larger if the comb finger and folded beam are tapered to +1° and −1°, respectively. The uneven deep fingers generate an abrupt force and displacement when the motion distance reaches the initial overlap length. The undercut reduces both the driving force and the mechanical stiffness of the lateral comb-drive actuator. The fabricated comb-drive actuator, with comb finger of +1° profile and 0.025 μm undercut, and folded beam of −1° slope and 0.075 μm undercut, is measured and compared with the models where both show consistent results. These analytical results can be used to compensate the fabrication tolerances at design stage and allow the actuators to provide more predictable performance.     

Modeling of a three-layer piezoelectric bimorph beam withhysteresis

Piezoelectric actuators are usually stacked or bimorph in configuration. In this paper the mechanics of a three-layer piezoelectric bimorph is discussed and its dynamic model with hysteresis is presented. The results can be used to analyze piezoelectric actuators constructed with three-layer piezoelectric bimorphs. A piezoelectric bimorph actuator has been fabricated and experiments have been carried out to verify the model. The calculated results of this model closely matched the tested results. This model can also be used with other types of piezoelectric actuators with a slight modification     

Performance of Electro-active paper actuators with thickness variation

This paper investigates the performance of electro-active paper (EAPap) actuators with thickness variation. EAPap made with cellulose paper, is attractive for biomimetic actuators due to its characteristics in terms of lightweight, biodegradable, dry condition, large displacement output, low actuation voltage and low power consumption. EAPap actuators exhibit a bending deformation in the presence of electric field. However, the performance is sensitive to the thickness of the EAPap material because the thickness is associated with the bending stiffness that strongly affects the bending deformation and the force output of the actuator. Thus, the performance of EAPap actuators that have three different samples of 20, 30, and 40 μm thicknesses is tested in terms of tip displacement, blocked force, electrical power consumption, and the efficiency. The sample preparation and the test methods are addressed. The resonance frequency and the bending stiffness are associated with the thickness of the EAPap actuator, and there is an optimum thickness for the best performance of the EAPap actuators. The mechanical output power and the efficiency at an optimal thickness are drastically improved comparing with the previous thickness case.     

A multilayer TWILA ultrasonic motor

A fully operational ultrasonic motor using bulk piezoelectric longitudinal actuators has been already introduced in our previous works. But despite of its interesting characteristics and its easily implementation, its high supply voltage (from 200 V_rms) could be a technological lock-in by imposing supplementary constraints in order to satisfy the electrical safety standards.To overcome this drawback, we have developed a new stator version which integrated multilayer longitudinal actuators, based on the bulk TWILA ultrasonic motor.If the global motor structure stays relatively closed to the bulk one, the new longitudinal actuator topology has been optimised with the help of a Finite Element Modeling.The higher capacitance value of the multilayer actuators requires the use of inductance compensation to optimise the motor drive.Finally, The mechanical performances are not only preserved but are now obtained under a main supply voltage (12 V_rms) 17 times lower than the previous bulk version. Moreover, the global efficiency is largely improved by reaching 20%.