Actuator Elements Research Articles

Automatic design of mechanical metamaterial actuators

Mechanical metamaterial actuators achieve pre-determined input–output operations exploiting architectural features encoded within a single 3D printed element, thus removing the need for assembling different structural components. Despite the rapid progress in the field, there is still a need for efficient strategies to optimize metamaterial design for a variety of functions. We present a computational method for the automatic design of mechanical metamaterial actuators that combines a reinforced Monte Carlo method with discrete element simulations. 3D printing of selected mechanical metamaterial actuators shows that the machine-generated structures can reach high efficiency, exceeding human-designed structures. We also show that it is possible to design efficient actuators by training a deep neural network which is then able to predict the efficiency from the image of a structure and to identify its functional regions. The elementary actuators devised here can be combined to produce metamaterial machines of arbitrary complexity for countless engineering applications.

Lighter and Stronger: Cofabricated Electrodes and Variable Stiffness Elements in Dielectric Actuators

The inherent compliance of soft robots often makes it difficult for them to exert forces on surrounding surfaces or withstand mechanical loading. Controlled stiffness is a solution to empower soft robots with the ability to apply large forces on their environments and sustain external loads without deformations. Herein, a compact, soft actuator composed of a shared electrode used for both electrostatic actuation and variable stiffness is described. The device operates as a dielectric elastomer actuator, while variable stiffness is provided by a shared electrode made of gallium. The fabricated actuator, namely variable stiffness dielectric elastomer actuator (VSDEA), has a compact and lightweight structure with a thickness of 930 μm and a mass of 0.7 g. It exhibits a stiffness change of 183×, a bending angle of 31°, and a blocked force of 0.65 mN. Thanks to the lightweight feature, the stiffness change per mass of the actuator (261× g−1) is 2.6 times higher than that of the other type of VSDEA that has no shared electrode.

Piezoelectric Scanning Micromirror With Built-In Sensors Based on Thin Film Aluminum Nitride

A micromirror with piezoelectric thin film aluminum nitride (AIN) as transducer material for actuation and detection is presented. Four sensor elements are integrated for closed-loop monitoring of the resonant driven microscanner with an entire footprint of 6 mm2. The sensor and actuator elements are monolithically fabricated in 150 mm SOI technology. The micromirror is characterized in terms of its scanning and sensor characteristics. A large optical scan angle of 137.9° (34.5° mechanical tilt angle corresponding) at 3385 Hz and 20 V actuation voltage is achieved. The median resonant voltage sensitivity is 4.7 °/V. For the sensor characterization, a cross-talk compensation is introduced, which significantly improves the signal quality and thus enables an accurate charge determination. The sensor signal increases linearly to the deflection. A dynamic sensor angle sensitivity of 48.4 fC/° is reached. Possible applications of the micromirror are consumer electronics, such as LIDAR or medical applications, such as fluorescence microscopy.

Pennate actuators: force, contraction and stiffness

Hierarchical actuators are comprised of multiple individual actuator elements arranged into a system, resulting in improved and expanded performance. Natural muscle tissue is a complex and multi-level example of hierarchical actuation, with its hierarchy spanning from the micrometer to the centimeter scale. In addition to a hierarchical configuration, muscle tissue exists in varying geometric arrangements. Pennate muscle tissue, denoted by its characteristic fibers extending obliquely away from the muscle tissue line of action, leverages geometric complexity to transform the relationship between fiber inputs and muscle tissue outputs. In this paper, a bioinspired hierarchical pennate actuator is detailed. This work expands on previous pennate actuator studies by deriving constitutive force, contraction, and stiffness models for a general pennate actuator, where the constituent fibers can be constructed from any linear actuator. These models are experimentally validated by studying a pennate actuator with McKibben artificial muscles constituting the actuator fibers. McKibben artificial muscles are used because they have a high force-to-weight ratio and are inexpensive to construct, making them an attractive candidate for hierarchical actuators and mobile robotics. Using the derived constitutive models, general pennate actuator performance is better understood by analyzing the transmission ratio, blocked force, and free contraction. Loaded contractions and stiffness during isotonic and isobaric contractions are also explored. The results allow for informed design decisions and an understanding of the associated tradeoffs when recreating the remarkable properties of pennate musculature. Future work will leverage the results of this paper to create an adaptive pennate actuator that is capable of changing configuration in response to force, contraction and stiffness demands.

Analysis of PI Controllers with Anti-Windup Techniques on Level Systems

The actuator element saturation for a long period of time can force high overshoot peaks in the physical system, in most cases, due to the integral action. Taking this effect into consideration, this work aims to present a case study considering this situation applied on a SMAR didactic level system, where an Anti-Windup Technique (AWT) with 5 distinct classic Proportional-Integral (PI) controllers were implemented. To validate its effectiveness, the results were always presented with the comparison of the use with and without AWT controlled responses. Also, the tests were carried out through implementations in MATLAB software, where the results showed a high necessity to use AWTs in these kind of systems. As for the controller’s tuning method efficiency, the integral of squared error index proved that the Cohen-Coon and Ziegler-Nichols controllers showed better results

Design and Experimental Analysis of Composite Material with Piezoelectric Layer

The main objective of this work is to analyze the active vibration control using smart sensors and actuators in a laminated E-Glass/epoxy cyanate composite beam. The cantilevered composite beam has piezoelectric ceramic patches as smart sensors and actuators. Hand layup technique for vibration suppression is done on the fabricated E-Glass/Epoxy-cyanate composite laminated beam. Experimental modal testing is performed to achieve vibration suppression on the flexible composite beam bonded with seven circular type piezoelectric actuator elements and seven circular type sensor elements. The complete vibration suppression utilizes a data acquisition system, a real-time control system, and a functional generator, in addition to the composite beam with PZT sensor and actuator. The data acquisition hardware consists of model NI 9233 (4 channel +5 V 24 Bit IEPE Analog input I2VA 1-to earth ground).

Modeling and simulation of a high-redundancy direct-driven linear electromechanical actuator for fault-tolerance under various fault conditions

The high-redundancy actuator (HRA) is a linear displacement actuation system, which consists of a large number of small electromechanical actuation elements arranged in a series and parallel configuration. The performance of a HRA with 9 direct-driven linear electromechanical actuators was analyzed under different fault conditions with the aid of the MATLAB simulation model. The results showed that the HRA has the capability to provide inherent fault-tolerance. Hence, the sudden failure of the system in the presence of fault was avoided. However, the capability of the actuator was found to be reduced gradually depending upon the number of faults.

Delay-dependent stability of pitch control system in a large wind turbine plant

The use of hydraulic pressure drive unit as actuator element in the pitch control scheme of a large wind turbine plant introduces inevitable time-delay in the feedback loop. This delay has an adverse impact on the performance and stability of the closed-loop system; nevertheless, if the delay magnitude exceeds a critical margin, the closed-loop system is driven to instability. In a large wind turbine plant, owing to its massive tower structure and enormous blade span, unstable, or for that matter, even marginally stable operation is highly detrimental. If the unboundedly evolving or sustained oscillations in pitch angle, signifying unstable or marginally stable operation respectively, are not curtailed using efficient braking systems, it might lead to the loss of whole structure. Hence, in this paper, the problem of delay-dependent stability of time-delayed pitch control system of a large wind turbine plant has been addressed using the classical Lyapunov-Krasovskii functional approach combined with Wirtinger inequality. The derived stability criterion which is in LMI framework, is tested on a benchmark wind turbine plant. In the sequel, simulation results are also provided to validate the effectiveness of the presented analytical results.

Hard Magnetic Properties of Co-Rich Microwires Crystallized by Current Annealing

Micromagnets in the form of microwires have become a subject of interest in various applications including magnetic field bias elements in miniature actuators, sensors, and manipulators. While the preparation of hard magnetic microwires with sufficiently high magnetization is a difficult task, it can be achieved by using specific crystallization techniques. We present a technique for the fabrication of micromagnets via controlled heat treatment of amorphous microwires using an electrical current. This crystallization technique converts a Co-rich microwire from a soft to a hard magnetic material. A large increase in coercivity (up to 580 Oe) is obtained after optimal current annealing (100 mA during 30–60 min). The crystallization consists of fine grains of mainly hcp-Co with an average size of 74 nm.

Design and implementation of battery charging system on solar tracker based stand alone PV using fuzzy modified particle swarm optimization

Design of battery charging system on solar tracker based PV system and its application has been presented in this paper. To improve the system performance, a solar tracking system as an innovative device of PV has been developed with an intelligent controller. PV equipped by solar tracker can significantly enhace its performance up to 40% of conventional system. In this research solar tracker designed has active tracking mode with double axis. In order to keep the PV performance optimum, a smart battery charging system has been developed and provided to store the electricity generated by PV system. A novel algorithm was implemented to the system which allows the battery charging process to operate quickly and safely. Besides, the components involved in the system are DC-DC converter, sensor, actuator and battery. DC-DC Converter used is Single Ended Primary Inductance Mode (SEPIM) with MOSFET as its actuator. Battery charging system has used intelligent control based on fuzzy-PSO algorithm. In this case, PSO functions to optimize and modify fuzzy parameters to obtain the best model. Optimized fuzzy controller has then been implemented and programmed in an Arduino microcontroller module to generate control signal which commands actuator element to control the voltage of battery through duty cycle manipulation variable. This algorithm has been able to improve the solar charging controller significantly and more convincingly increase PV performance.

The buckling beam as actuator element for on-off hydraulic micro valves

The application of buckling beams for two types of micro valve actuation is studied in this paper by mathematical models. The first application type is the magnification of a short stroke actuator, such as piezo-electric stacks, to obtain the required stroke of the valve spool. The second application is the realisation of a spring with negative spring constant as an essential function element of a passive hydraulic binary counter which can control several binary coded valves by one flow control valve. The toggle mechanism as reference solution is mathematically analysed to elucidate the main properties. Four types of beams, only differing by their support structure, are analysed by analytical models employing a Rayleigh-Ritz approach. Models are evaluated to assess the performance properties of these beam types and to provide first order design rules.

ANÁLISE COMPARATIVA ENTRE MÉTODOS DE CONTROLE APLICADOS PARA ATENUAÇÃO DE VIBRAÇÕES EM UMA SUSPENSÃO AUTOMOTIVA

Automotive suspension is one of the equipment present in a vehicle and is used to preserve its structural integrity. When used, this device uses passive actuation elements (usually springs and dampers) to perform vibration attenuation, however some companies, including Audi, have been using a semi-active control for the same function claiming that there are gains over conventional systems. . Another method commonly used in automotive suspensions is active controls, already applied to Formula 1 by Willians in 1992. This work is dedicated to the study and evaluation of the difference in behavior of an automotive suspension when subjected to each of the three control methods.

3D-Printed Scanning-Probe Microscopes with Integrated Optical Actuation and Read-Out.

Scanning-probe microscopy (SPM) is the method of choice for high-resolution imaging of surfaces in science and industry. However, SPM systems are still considered as rather complex and costly scientific instruments, realized by delicate combinations of microscopic cantilevers, nanoscopic tips, and macroscopic read-out units that require high-precision alignment prior to use. This study introduces a concept of ultra-compact SPM engines that combine cantilevers, tips, and a wide variety of actuator and read-out elements into one single monolithic structure. The devices are fabricated by multiphoton laser lithography as it is a particularly flexible and accurate additive nanofabrication technique. The resulting SPM engines are operated by optical actuation and read-out without manual alignment of individual components. The viability of the concept is demonstrated in a series of experiments that range from atomic-force microscopy engines offering atomic step height resolution, their operation in fluids, and to 3D printed scanning near-field optical microscopy. The presented approach is amenable to wafer-scale mass fabrication of SPM arrays and capable to unlock a wide range of novel applications that are inaccessible by current approaches to build SPMs.

A Lumped-Mass Model for Large Deformation Continuum Surfaces Actuated by Continuum Robotic Arms

AbstractCurrently, flexible surfaces enabled to be actuated by robotic arms are experiencing high interest and demand for robotic applications in various areas such as healthcare, automotive, aerospace, and manufacturing. However, their design and control thus far has largely been based on “trial and error” methods requiring multiple trials and/or high levels of user specialization. Robust methods to realize flexible surfaces with the ability to deform into large curvatures therefore require a reliable, validated model that takes into account many physical and mechanical properties including elasticity, material characteristics, gravity, external forces, and thickness shear effects. The derivation of such a model would then enable the further development of predictive-based control methods for flexible robotic surfaces. This paper presents a lumped-mass model for flexible surfaces undergoing large deformation due to actuation by continuum robotic arms. The resulting model includes mechanical and physical properties for both the surface and actuation elements to predict deformation in multiple curvature directions and actuation configurations. The model is validated against an experimental system where measured displacements between the experimental and modeling results showed considerable agreement with a mean error magnitude of about 1% of the length of the surface at the final deformed shapes.

Comparison of Electrophysical Properties of PZT-Type Ceramics Obtained by Conventional and Mechanochemical Methods.

In the paper, the multicomponent PZT-type ceramics with Pb(Zr0.49Ti0.51)0.94Mn0.015Sb0.01W0.015Ni0.03O3 composition have been obtained by conventional and mechanochemical methods. With conventional ceramic technology, PZT-type ceramics have been synthesized by the method of calcination powder (850 °C/4 h). Instead of this step, the mechanochemical synthesis process for different milling periods (15 h, 25 h, 50 h, 75 h) has been applied for a second batch of samples. To obtain the dense PZT-type ceramic samples, powders have been sintered by free sintering method at conditions of 1150 °C/2 h. Studies have shown that the perovskite structure of the PZT-type material is formed during mechanochemical activation of powders during the technological process at low temperature. The application of the mechanochemical synthesis to obtain the PZT-type materials also allows shortening of the technological process, and the useful electrophysical properties of ceramic samples are not reduced at the same time. The presented results have confirmed that the investigated materials can be used in microelectronic applications, especially as elements of actuators and piezoelectric transducers.

An Enhanced Time-Reversal Imaging Algorithm-Driven Sparse Linear Array for Progressive and Quantitative Monitoring of Cracks

A Lamb wave and linear piezoelectric lead zirconate titanate (PZT) array-based monitoring method for the detection and quantification of crack damage is presented in this paper. Because existing PZT array arrangements are not suitable for quantitative monitoring of crack damage both in orientation and in length, a sparse linear PZT array is introduced and applied to collect crack reflections. Based on this new array, a method for estimating crack orientation is proposed. An amplitude spectrum as a function of angle is mapped using time delayed and summed signals. By finding the peaks in the spectra, the central actuator element and corresponding orientation angle are determined. Furthermore, the time of flight imaging method is modified to display and evaluate cracks quantitatively. Validating experiments are conducted on a T6061 aluminum plate, monitoring and evaluating single and connected cracks with various orientations in different locations. As suggested by the experiments, the orientation of most cracks can be well recognized and all cracks can be quantitatively displayed by the proposed methods.

A digital microfluidic diluter-based microalgal motion biosensor for marine pollution monitoring

Marine pollution and monitoring have received more and more concern in recent years. Herein, a fully automatic whole-algae biosensor was designed for low-cost and fast detection of toxic contaminants in seawater. It consists of a digital microfluidic (DMF) diluter chip, an actuation element, a detector element, and a microalgae bioreporter. A feedback-control protocol based on charging-time compensation was introduced. It ensures precise actuation of the droplet with diverse salty concentrations and contents in the marine environment. The two-mixer cross-split dilution engine increases the accuracy of droplet dispensing and concentration diluting. By selecting motility of P. subcordiformis as the sensor signal, the developed biosensor showed good sensitivity and robustness for a wide range of salinity (10–37‰), temperature (0–25 °C), light levels (0–325 μmol photons m−2 s−1), and cell density factor (1.0–4.0). The biosensor responses were examined in the presence of copper, lead, phenol, and nonylphenol (NP). In all cases, toxic responses (i.e. dose-related inhibition of algal motion) were detected with the detection limits of 0.65 μmol.L−1, 1.90 μmol.L−1, 2.85 mmol.L−1, and 5.22 μmol.L−1 respectively. These results were obtained in a much shorter time (2 h for our biosensor vs. 24 h-10 d for growth inhibition test) and the data are consistent with previous classical studies. We thus developed a simple, rapid, and adaptable system for marine routine monitoring and early-warning detection for lab and on-site applications.

A dynamic metasurface in the mix

Metasurfaces Metasurfaces have been designed and fabricated to function as many passive optical elements. A time-dependent active element can now be obtained by marrying concepts in microelectromechanics with an array of one-dimensional dielectric nanowires. Although such a static array has been used to select for desired wavelengths, the wavelength is dependent on the nanowire-to-substrate separation. Holsteen et al. added a voltage-controlled actuation element to the design that could steer light beams as well as select and mix certain colors. The fast actuation capability could affect applications ranging from autonomous vehicles to augmented and virtual reality systems. Science , this issue p. [257][1] [1]: /lookup/doi/10.1126/science.aax5961

Design, test and control of a compact piezoelectric scanner based on a compound compliant amplification mechanism

This paper presents the mechanical design, testing and control of a novel piezoelectric scanner to achieve high performance motion tracking. Based on both triangle amplification and differential principles, the scanner is designed with a compound compliant amplification mechanism (CCAM) to realize deflection motion. A strain-type piezoelectric actuator is adopted as the actuation and angle-sensing element for the scanner. Analytical calculations in terms of deflection range, sensor deployment and dynamics are derived, and then the finite element analysis and prototype tests are conducted to verify the analytical results. To facilitate precise angular tracking in front of the existing hysteresis effect, a terminal sliding mode control scheme is implemented for the performance improvement. Experimental results reveal that the developed scanner has an angle resolution of 1.5 μrad, a motion range of ±0.16 mrad, and can achieve accurate angle tracking performance.

4D Printing Self-Morphing Structures.

The main objective of this paper is to introduce complex structures with self-bending/morphing/rolling features fabricated by 4D printing technology, and replicate their thermo-mechanical behaviors using a simple computational tool. Fused deposition modeling (FDM) is implemented to fabricate adaptive composite structures with performance-driven functionality built directly into materials. Structural primitives with self-bending 1D-to-2D features are first developed by functionally graded 4D printing. They are then employed as actuation elements to design complex structures that show 2D-to-3D shape-shifting by self-bending/morphing. The effects of printing speed on the self-bending/morphing characteristics are investigated in detail. Thermo-mechanical behaviors of the 4D-printed structures are simulated by introducing a straightforward method into the commercial finite element (FE) software package of Abaqus that is much simpler than writing a user-defined material subroutine or an in-house FE code. The high accuracy of the proposed method is verified by a comparison study with experiments and numerical results obtained from an in-house FE solution. Finally, the developed digital tool is implemented to engineer several practical self-morphing/rolling structures.