Bimorph Actuator Research Articles

A Low Mass Power Electronics Unit to Drive Piezoelectric Actuators for Flying Microrobots

This paper presents a power electronics design for the piezoelectric actuators of an insect-scale flapping-wing robot, the RoboBee. The proposed design outputs four high-voltage drive signals tailored for the two bimorph actuators of the RoboBee in an alternating drive configuration. It utilizes fully integrated drive stage circuits with a novel highside gate driver to save chip area and meet the strict mass constraint of the RoboBee. Compared with previous integrated designs, it also boosts efficiency in delivering energy to the actuators and recovering unused energy by applying three power saving techniques, dynamic common mode adjustment, envelope tracking, and charge sharing. Using this design to energize four 15 nF capacitor loads with a 200 V and 100 Hz drive signal and tracking the control commands recorded from an actual flight experiment for the robot, we measure an average power consumption of 290 mW.

Programmable and functional electrothermal bimorph actuators based on large-area anisotropic carbon nanotube paper

Electro-active polymer (EAP) actuators, such as electronic, ionic and electrothermal (ET) actuators, have become an important branch of next-generation soft actuators in bionic robotics. However, most reported EAP actuators could realize only simple movements, being restricted by the small area of flexible electrodes and simple designs. We prepared large-area flexible electrodes of high anisotropy, made of oriented carbon nanotube (CNT) paper, and carried out artful graphic designs and processing on the electrodes to make functional ET bimorph actuators which can realize large bending deformations (over 220°, curvature > 1.5 cm−1) and bionic movements driven by electricity. The anisotropy of CNT paper benefits electrode designs and multiform actuations for complex actuators. Based on the large-area CNT paper, more interesting and functional actuators can be designed and prepared which will have practical applications in the fields of artificial muscles, complicated actuations, and soft and bionic robotics.

Micro converter with a high step-up ratio to drive a piezoelectric bimorph actuator applied in mobile robots

In this study, a micro converter for driving a piezoelectric actuator is designed and implemented. The converter can produce 100 V, 80 Hz AC voltage from 3.7 V DC voltage. With regard to the requir...

Graphene-based bimorphs for micron-sized, autonomous origami machines

Origami-inspired fabrication presents an attractive platform for miniaturizing machines: thinner layers of folding material lead to smaller devices, provided that key functional aspects, such as conductivity, stiffness, and flexibility, are persevered. Here, we show origami fabrication at its ultimate limit by using 2D atomic membranes as a folding material. As a prototype, we bond graphene sheets to nanometer-thick layers of glass to make ultrathin bimorph actuators that bend to micrometer radii of curvature in response to small strain differentials. These strains are two orders of magnitude lower than the fracture threshold for the device, thus maintaining conductivity across the structure. By patterning 2-[Formula: see text]m-thick rigid panels on top of bimorphs, we localize bending to the unpatterned regions to produce folds. Although the graphene bimorphs are only nanometers thick, they can lift these panels, the weight equivalent of a 500-nm-thick silicon chip. Using panels and bimorphs, we can scale down existing origami patterns to produce a wide range of machines. These machines change shape in fractions of a second when crossing a tunable pH threshold, showing that they sense their environments, respond, and perform useful functions on time and length scales comparable with microscale biological organisms. With the incorporation of electronic, photonic, and chemical payloads, these basic elements will become a powerful platform for robotics at the micrometer scale.

A MEMS Based Fourier Transform Spectrometer and Its Scan Stability Study

An Fourier Transform Spectrometer (FTS) based on an H-shaped electrothermally actuated microelectromechanical system (MEMS) scanning mirror has been developed. The MEMS scanning mirror can generate about 200 μm at 5 Hz with only 5 Vpp and maintain a very small tilting of about 0.029° without using any complex compensation or closed-loop control. This high scanning performance is achieved by using a unique H-shaped frame supported by symmetrically distributed thirty-two pairs of innovative three-level-ladder bimorph actuators. This MEMS FTS can cover a wide spectral range of 1000–2500 nm. A spectral resolution of 64.1 cm−1, or 11 nm at 1310 nm, is achieved.

Design and experiment of a small-scale walking robot employing stick-slip motion principle.

We describe the design and control of a four legged walking robot, 45 g in weight and 130 mm × 105 mm × 25 mm in size. Each leg consists of two piezoelectric bimorph actuators that are bonded at the free end by a flexure and an end-effector. The robot generates stick-slip locomotion when applying sawtooth shaped voltage signals. Friction between legs and a contact surface is analyzed by using the Coulomb friction model. Locomotion characteristics are measured in several experiments. The robot was driven with frequencies up to 75 Hz, and a maximum velocity of 65 mm/s was obtained at two frequencies: 45 Hz with 190 Vpp driving voltage and 60 Hz with 170 Vpp driving voltage, respectively.

Development of large-movements and high-force electrothermal bimorph actuators based on aligned carbon nanotube reinforced epoxy composites

By using aligned multi-walled carbon nanotube (MWCNT) reinforced epoxy composites possessing a negative coefficient of thermal expansion (CTE) as well as high Young’s modulus and aluminum foils, novel electrothermal bimorph actuators are fabricated. U-shaped bimorph actuators are formed by cutting out the middle part of the composite/aluminum laminates, where the MWCNT-aligned direction is parallel to the length direction of the U-shaped bimorph actuators. We demonstrate that the bimorph actuators with a free length of 16mm show a large bending displacement and force output, and their values are 7.6–10.0mm and 0.8–7.8mN under a DC voltage of 5.2–6.0V. Based on these results, the bending displacement and force output of the bimorph actuator are modeled by combining strength-of-materials theories and rule of mixtures (Voigt model and Turner’s model). By using these models, we indicate contributions from two sources toward the increased bending displacement and force output in the bimorph actuator: (i) designing the Young’s modulus and negative CTE of the composite layer by controlling the MWCNT volume fraction and the dimensional parameters (especially thickness) of the bimorph actuator; (ii) selecting materials having a high Young’s modulus as well as a large CTE as the second layer.

Enabling PZT bimorph actuator with passive polysilicon structure

For the first time, a bimorph thin film lead zirconate titanate (PZT) micro-actuator with thick polysilicon as a passive structural layer is reported. A simple micro-cantilever actuator consisting of 1000 µm long and 250 µm wide with 4 µm thick polysilicon structure flanked by a piezoelectric active layer on the top and bottom side has been fabricated to demonstrate such novel bimorph configuration. The actuator displays a flat profile with only 2 µm of tip deflection which indicates a balanced stress distribution in the structure. It is driven alternatively in both directions, demonstrating its unique suitability for micro-actuation mechanisms where a passive structural layer is required to enhance the mechanical performance and reliability of the system. The static and dynamic measurements show similar characteristics for the top and bottom actuation. The actuator has a measured resonance frequency of 6.3 kHz, and displacement voltage sensitivities of 17.9 and 25.6 nm/V in the upward and downward direction, respectively.

Bimorph Actuator: a New Instrument for Time-Resolved X-ray Diffraction and Spectroscopy

A new approach to time-resolved X-Ray experiments implementation at both laboratory X-Ray sources and synchrotron facilities is presented. A time resolution of few milliseconds per one rocking curve measurement can be reached by using a new X-Ray optics element – vibrating bimorph actuator based on a bidomain bending-type crystal of lithium niobate. The ranges of X-Ray beam angular or energy changeover are defined by the actuator operational mode and resonant response. The time and spatial parameters for X-ray optical element based on bimorph actuator have been estimated. The ranges of actuator angular changeover in a dynamical mode at various frequencies (including resonance) of bidomain crystal vibrations have reached up to 100 arcseconds in а quasistatic mode and more than 500 arcseconds in а resonance mode at the control voltage of 22 V and vibration frequency up to 8 kHz (which corresponds to time resolution of 0.125 milliseconds). The numerical algorithms for processing of the experimental data measured using the bimorph optical element have been developed. The examples of X-Ray beam angular changeover reached in different actuator vibration modes and possible application of such approach are presented in the work.

Investigation of dynamic thermal behaviors of an electrothermal micromirror

It is well known that the heat transfer at microscale is quite different from that at macroscale, but the dynamic thermal behavior of micro-actuators with movable microstructures still lacks comprehensive investigation. This work presents a thorough study on thermal behaviors of an electrothermally actuated scanning micromirror, which has a 1mm×1mm central mirror plate supported on four sides by four pairs of electrothermal bimorph actuators. The heat transfer from the thermal actuator to the ambience, including the substrate and the environmental air, are investigated experimentally with several different driving powers and various frequencies under natural convection, forced convection, and in vacuum. The results indicate that the heat conduction dominates the heat transfer process of electrothermal bimorph actuators, while the convection has little impact on the overall heat transfer even under strong forced convection. Furthermore, an equivalent circuit model of the electrothermal micromirror is developed and experimentally verified, from which the effective heat transfer coefficient of the electrothermal bimorphs is extracted to be in the range from 1900 to 2282W/(m2K), which is one to two orders of magnitude larger than that at macroscale.

Multi-objective optimization of a triple layer piezoelectric bender with a flexible extension using genetic algorithm

ABSTRACTThis article presents an electromechanical analysis for a piezoelectric bimorph actuator with a flexible extension, which is used to increase the tip deflection. The performance measuring attributes of such an actuator are derived, and a genetic algorithm is used for multi-objective optimization. The analysis reveals that for a thick flexible extension, the length of the extension provides Pareto optimal solutions for multi-objective optimization. The analysis also shows that as the thickness of the flexible extension decreases, the Pareto optimal solutions converge to a single solution for multi-objective optimization. We have considered nonlinear deflection behavior of piezoelectric materials at high electric fields, and series and parallel electrical connections in the analysis.

Performance improvement of a piezoelectric bimorph actuator by tailoring geometry

ABSTRACTThis article illustrates performance improvement of a piezo-bimorph actuator by tailoring its geometry. We have analytically presented that a piezo-bimorph actuator with a tapered surface provides superior performance for out-of-plane bending compared to a rectangular surface while having equal mass and equal primary capacitance. Equal capacitance ensures equal input electrical energy and bandwidth for both the cases below its first resonant frequency. We have analytically derived performance measuring attributes of such an actuator considering high electric field, and shown the performance improvement quantitatively. We have also presented finite element solutions to compare with the analytical solutions. Some results are validated with the earlier published experimental results.

Water skating robots take off?

An insect-inspired microbot that uses the motion of its wings to skate across the surface of water at high speed is presented in work from China aimed at creating microbots that can also fly. The water strider-inspired microbot's hydrophobic legs allow it to stand on the surface of the water thanks to surface tension. Bioinspired engineering seeks to create technology based on ideas taken from the amazing and varied biology we see around us everyday. Insects are a rich source of that inspiration, with their wide range of specialised abilities, including the ability to walk on water using surface tension displayed by gerridae such as the water strider. A group of researchers at Shanghai Jiao Tong University have been working on robots that can copy this feat, because, as team member Prof. Weiping Zhang explained, “Water striders can support themselves stably and move rapidly on the water. We feel that this is a very low energy consumption mechanism, especially in insect-scale.” In this issue of Electronics Letters, Prof. Zhang and his colleagues present a micro-bionic robot that can move quickly on the water, using flapping-wings and skating-legs, and is, they say, the lightest and one of the fastest water skating robots ever developed. Weighing just 165mg, their robot can skate across the surface of water at 151mm/s but Prof. Zhang tells us that these achievements are only a part of the significance of this work, “First, the study develops an efficient movement for aquatic robots, which can significantly improve the robot's working duration and cruising radius. Second, this study successfully combines the large thrust generation mechanism of flapping-wings flight and the low resistance movement form of surface tension skating to lay the technical foundation for further development of flight-skating amphibious robots.” This study was also the world's first attempt to combine these two forms of motion, and achieved a certain degree of movement performance. Previous studies have focused on actively driving a robot's legs to achieve water skating. The leg-driving approach produces motion through direct interaction with the water surface, using a rowing-like motion to push the robot forward. Unfortunately, at higher driving frequencies it is easy to break the water surface with this skating method, so it is difficult to increase the skating speed. The Shanghai team have avoided this problem by decoupling the drive mechanism from their robot's legs. Instead of driving the legs directly they use the flapping mechanism of the robot's flexible wings as the drive mechanism; producing aerodynamic force to move the robot across the water's surface. This increases stability and allows a higher skating speed, it also improves manoeuvrability. All of which can be controlled by adjusting the frequency of flapping motion. The motion of the robot's wings is produced by lead zirconate titanate (PZT) piezoelectric actuators; a method already used in flying robot designs. The wings themselves are made from polyester film with carbon fibre ‘veins’. The microbot stands on the water surface thanks to titanium alloy legs with a hydrophobic coating. The flapping wing laser displacement test equipment in the lab at Shanghai Jiao Tong University. Inset: The robot's polyester film wings incorporate carbon fibre 'veins'. These wings, rather than the legs, are used to drive the robot's water skating. The exact details of these tiny components in combination are key to the success of the work. “The major challenges we faced were the design of the wings and legs,” says Zhang. “Aerodynamic elastic deformation of flexible wings occurs when they flap at a high frequency, while large deflection elastic deformation of the titanium alloy legs treated with hydrophobic coating also happens when it undertakes a load during the movement of robot. We must ensure the stability of the forces produced by these two kinds of deformation, through the bionic design of veins, symmetrical distribution and horizontal assembly of wings, symmetrical PZT bimorph actuator design, periodic alternating signal and centre of gravity design.” The Shangai team are now working to further optimise the structural design of their microbot and develop their multi-DOF control technology; with the ultimate aim of producing an amphibious robot that can fly and skate with multiple degrees of freedom. The next step in the work is to further study the aerodynamic control mechanism and attempt to change the amplitude and direction of the aerodynamic forces produced in order to achieve transition between flight and water-skating. In terms of using such robots they foresee applications in aquatic detection, signal collection, military reconnaissance, marine meteorology and water pollution monitoring. “With such low-cost, low-power, fast-moving microbots as a platform, a mobile sensor network can be built up, effective distributed operations can be achieved as well.”

Programmable molecular composites of tandem proteins with graphene oxide for efficient bimorph actuators

The rapid expansion in the spectrum of two-dimensional (2D) materials has driven research efforts on the fabrication of 2D composites and heterostructures. Highly ordered structure of 2D materials provides an excellent platform for controlling the ultimate structure and properties of the composite material with precision. However, limited control over the structure of the matrix phase and its interactions with highly ordered 2D materials results in defective composites with inferior performance. Here, we demonstrate the successful synthesis, integration, and characterization of hybrid 2D material systems consisting of tandem repeat (TR) proteins inspired by squid ring teeth and graphene oxide (GO). The TR protein layer acts as a unique programmable assembler for GO layers with precise control of interlayer distance of less than 1 nm. As an application, we further demonstrate thermal actuation using bimorph molecular composite films. Bimorph actuators made of molecular composite films (GO/TR) can lead to energy efficiencies 18 times higher than regular bimorph actuators consisting of a GO layer and a TR protein layer (i.e., conventional bulk composite of GO and TR). Additionally, molecular composite bimorph actuators can reach curvature values as high as 1.2 cm−1 by using TR proteins with higher molecular weight, which is 3 times higher than conventional GO and TR composites.

Piezoelectric d36 in-plane shear-mode of lead-free BZT-BCT single crystals for torsion actuation

We report the study of piezoelectric direct torsion actuation mechanism using lead-free piezoelectric d36 in-plane shear-mode BZT-BCT single crystals. The generated angle of twist of the piezoelectric torsion actuator was obtained from the transverse deflection measurement using a laser vibrometer. The bi-morph torsional actuator, consisting of two lead-free piezoelectric BZT-BCT in-plane shear-mode single crystals with a giant piezoelectric d36 shear strain coefficient of 1590 pC/N, provided a rate of twist of 34.12 mm/m under a quasi-static 15 V drive. The experimental benchmark was further modelled and verified by the ANSYS software using three dimensional (3D) piezoelectric finite elements. The experimental results revealed that lead-free piezoelectric BZT-BCT d36-mode single crystal is a superior candidate for piezoelectric torsion actuation. This lead-free piezoelectric BZT-BCT d36-mode torsion actuator can be effectively applied in torsional deformation control by taking into account the environmental considerations.

Soft electrothermal actuators using silver nanowire heaters.

Low-voltage and extremely flexible electrothermal bimorph actuators were fabricated in a simple, efficient and scalable process. The bimorph actuators were made of flexible silver nanowire (AgNW) based heaters, which exhibited a fast heating rate of 18 °C s-1 and stable heating performance with large bending. The actuators offered the largest bending angle (720°) or curvature (2.6 cm-1) at a very low actuation voltage (0.2 V sq-1 or 4.5 V) among all types of bimorph actuators that have been reported to date. The actuators can be designed and fabricated in different configurations that can achieve complex patterns and shapes upon actuation. Two applications of this type of soft actuators were demonstrated towards biomimetic robotics - a crawling robot that can walk spontaneously on ratchet surfaces and a soft gripper that is capable of manipulating lightweight and delicate objects.

A programmable soft chemo-mechanical actuator exploiting a catalyzed photochemical water-oxidation reaction.

We describe a composite hydrogel containing an embedding coupled chemistry for light-sensitized catalytic reactions that enables chemo-mechanical actuation of poly(acrylic acid)-based gels. In these materials, a photosensitizer and catalyst-ruthenium trisbipyridine and iridium dioxide nanoparticles, respectively-are incorporated into the hydrogel where together, with visible light irradiation, they undergo a catalytic water-oxidation reaction that lowers the pH and induces a dissipative/chemically-driven strain change in the gel. To demonstrate the capacity for 3D chemo-mechanical actuation, a layer of non-pH responsive poly(2-hydroxyethyl methacrylate) is added to the photo-active composite gel to create a model bimorph actuator. Triggering and terminating the water-oxidation reaction leads to a programmatic expansion and contraction of the active layer, which induces different modes of biomimetic curling motions in the bimorph actuator in light and dark environments. The efficiency of this system is fundamentally limited by the system-level design, which provides no capacity to sustain a local pH gradient against diffusive mixing. Even so, if the initial pH of the background solution is reestablished either actively or passively between each reaction cycle, it is possible to realize multiple cycles of reversible actuation. We describe a thermodynamic analysis of this system which identifies specific features mediating efficiency losses and conceptual requirements for mesoscopic design rules for optimization of this system and for advancing soft actuation systems in general.

改良Bouc-Wenモデルを用いたピエゾアクチュエータのヒステリシス特性のモデル化

This paper discloses the development of the improved Bouc-Wen model which captures the behavior of the rate dependent hysteresis of a piezoelectric actuator. The basic form of the Bouc-Wen model only exhibits symmetric hysteresis loop for a sinusoidal input with no DC offset, whereas the real world bi-morph type actuator occasionally exhibits asymmetric loop for the same stimuli. The present works also proposes the integration of the FIR filter to the model to capture phase lag caused by the structural oscillation of the actuator. Comparison of the modeling accuracy has been given with our recent work of adaptive Preisach model. The result shows that accuracy of the two models are almost the same but the intrinsic difference lies in the number of parameters to be determined to form a computable model: the proposed model has only 25 parameters whereas the adaptive Preisach model includes 5050 discretized distribution function values to establish a single model.

Effect of self-induced electric displacement field on the response of a piezo-bimorph actuator at high electric field

This paper analytically illustrates the response of a piezoelectric bimorph actuator considering the effect of self-induced electric displacement field. In the analysis, we have considered response of the actuator at high electric field. The self-induced electric displacement field exists inside the piezoelectric actuator during its bending. This effect was not considered in the earlier modeling, which typically followed stress-strain based approaches, instead of following the extended Hamilton's principle for electromechanical systems driven by constant voltage source. This electric displacement field affects the tip deflection of a piezoelectric actuator. The new derivation based on Hamilton's principle also shows that a piezo-bimorph's short circuit stiffness, which was considered independent of the piezoelectric coupling coefficient in earlier literature, actually depends on the piezoelectric coupling coefficient. A piezoelectric material of high piezoelectric coupling coefficient can produce a significant self-induced electric displacement field, which can significantly impact the tip deflection and the stiffness of a piezoelectric bimorph actuator. The analytical results are validated with the experimental results, published in earlier literature.

Electrothermal Actuators for SiO₂ Photonic MEMS.

This paper describes the design, fabrication and characterization of electrothermal bimorph actuators consisting of polysilicon on top of thick (>10 ) silicon dioxide beams. This material platform enables the integration of actuators with photonic waveguides, producing mechanically-flexible photonic waveguide structures that are positionable. These structures are explored as part of a novel concept for highly automated, sub-micrometer precision chip-to-chip alignment. In order to prevent residual stress-induced fracturing that is associated with the release of thick oxide structures from a silicon substrate, a special reinforcement method is applied to create suspended silicon dioxide beam structures. The characterization includes measurements of the post-release deformation (i.e., without actuation), as well as the deflection resulting from quasi-static and dynamic actuation. The post-release deformation reveals a curvature, resulting in the free ends of 800 long silicon dioxide beams with 5 -thick polysilicon to be situated approximately 80 above the chip surface. Bimorph actuators that are 800 in length produce an out-of-plane deflection of approximately 11 at 60 dissipated power, corresponding to an estimated 240 actuator temperature. The delivered actuation force of the 800 -long bimorph actuators having 5 -thick polysilicon is calculated to be approximately 750 at 120 .