Array Of Actuators Research Articles

Dynamic control of high-voltage actuator arrays by light-pattern projection on photoconductive switches

The ability to control high-voltage actuator arrays relies, to date, on expensive microelectronic processes or on individual wiring of each actuator to a single off-chip high-voltage switch. Here we present an alternative approach that uses on-chip photoconductive switches together with a light projection system to individually address high-voltage actuators. Each actuator is connected to one or more switches that are nominally OFF unless turned ON using direct light illumination. We selected hydrogenated amorphous silicon (a-Si:H) as our photoconductive material, and we provide a complete characterization of its light to dark conductance, breakdown field, and spectral response. The resulting switches are very robust, and we provide full details of their fabrication processes. We demonstrate that the switches can be integrated into different architectures to support both AC and DC-driven actuators and provide engineering guidelines for their functional design. To demonstrate the versatility of our approach, we demonstrate the use of the photoconductive switches in two distinctly different applications—control of µm-sized gate electrodes for patterning flow fields in a microfluidic chamber and control of cm-sized electrostatic actuators for creating mechanical deformations for haptic displays.

Scalable Fluidic Matrix Circuits for Controlling Large Arrays of Individually Addressable Actuators

A fundamental challenge of pneumatically powered soft robotic devices is the scalability of fluidic control systems to address each actuated degree of freedom, as the required electromechanical valves are bulky and expensive. Previous solutions have compromised the reprogrammability and/or the bandwidth of the fluidic system. This article describes and models a fluidic subsystem, a fluidic matrix circuit (FMC), that enables the independent control of many () actuators using a limited number () of electromechanical valves. The fundamental unit, a fluidic logic module (FLM), generates a bidirectional pressure signal (vacuum or positive pressure) based on the state of the mass flow through it. Thus and array of pneumatic actuators can be addressed individually using an array of FLMs integrated into a matrix (i.e., an FMC), with electromechanical valves to switch the mass flow through each row and column of the matrix. The resulting refresh rates are an order of magnitude faster than previous approaches. This concept with a prototype FMC able to control 25 actuators using 10 electromechanical valves for applications including a fluidic shape display and a wearable haptic vest is demonstrated. This approach could enable more complex and sophisticated soft robotic devices with scalable control hardware.

A modified hyperbola based baseline free approach using Lamb wave mode conversion for detection of multiple structural damages: a simulation based study

Guided wave based techniques are among the promising techniques for structural health monitoring due to their ability to detect damage with high precision, ability to scan large area and low power consumption. However, practical implementation of these techniques to structures with relatively complex geometries such as stiffened plates demand further research due to several challenges. Some of such challenges include the presence of stiffeners and edges in close vicinity causing multiple reflections of waves, possibility of multiple damages and lack of baseline data. To address all these issues, a modified hyperbola based approach using mode converted signal and a data based matching scheme has been proposed in this paper. A stiffened plate is taken as the example structure. Corrosion like defects have been considered as the damages. Each panel of the stiffened plate has been scanned separately through phased array actuation. The effectiveness and robustness of the proposed approach have been shown through a case study using 3D finite element simulation data.

Experimental investigation of synthetic jet control of wing rock for a flying wing aircraft

Flying wing aircraft easily experience wing rock due to the lack of lateral-directional stability, which causes serious challenges to flight control and safety. Thus, it is necessary to reduce the wing rock amplitude or reduce the mean roll angle by additional control. For a flying wing model with a 65° leading-edge sweep, we propose a strategy using an array of synthetic jet actuators to control the wing rock. The control effect and mechanism are studied by attitude measurement and particle image velocimetry measurement in a wind tunnel; the results confirm that the synthetic jet can effectively change the trim position of the wing rock. The control effect is affected by the angle of attack, Reynolds number, actuation position, actuation voltage, and frequency. In general, downstream actuators perform better at low angles of attack, while upstream actuators perform better at high angles of attack; the actuators positioned at the downward rolling side have a better effect than those positioned at the upward side. Furthermore, continuously variable control of the trim position can be achieved by changing the actuation voltage or modulation frequency, which provides a base for attitude manipulation by using active flow control instead of a mechanical control surface. Quantitative analysis of the flow field indicates that the leading-edge vortex on the upward side provides a rolling moment, while the recirculation zone on the downward side also contributes to the wing rock. This is a dynamic process, causing the flying wing to balance at a nonzero mean roll angle. The synthetic jet positioned at the downward rolling side can transport high-momentum fluids to the near-wall region, thereby suppressing flow separation and reducing the size of the recirculation zone. This enhances the lift on the control side and thus reduces the mean roll angle of the wing rock.

Fabrication ofShearing‐Motion‐TypeTactile Display Mechanism UsingSMA Thick‐FilmActuators and Coil Springs Array

AbstractA shearing‐motion‐type microelectromechanical system (MEMS) tactile display mechanism was fabricated to provide a shear vibration stimulus to the fingertip. It consisted of shrinking shape memory alloy (SMA) thick‐film actuators and a supporting coil spring array. The SMA actuator array was designed and fabricated using a flash‐evaporated SMA film (10 μm thick) on a mirror‐polished Cu substrate. The coil spring was successfully arrayed on a glass substrate with an SU‐8 circular array pattern. The glass substrate with the coils was bonded to the SMA substrate to complete the shearing‐motion mechanism. During the bonding process, the SMA actuators were initially elongated by the coil springs. The generated amplitude and force of the fabricated mechanism were characterized when the SMA actuator was heated by applying a pulsed current to be shrank by the shape recovery effect. The fabricated shearing‐motion mechanism successfully generated large amplitude of 41 μm (around 80 μm in reciprocal motion) and force of 22 mN at a driving frequency of 1 Hz. At 20 Hz, an amplitude of 23 μm and force of 10 mN were obtained even though they were reduced owing to the low thermal response. At both driving frequencies, the obtained amplitudes and forces seems to be sufficient for tactile stimulation to finger skin. © 2023 Institute of Electrical Engineer of Japan and Wiley Periodicals LLC.

Piezoelectric deformable mirror driven by unimorph actuator arrays on multi-spatial layers.

In order to reduce the cost of the piezo actuator array deformable mirror (DM), a piezoelectric DM driven by unimorph actuator arrays on multi-spatial layers is proposed. The actuator density can be multiplied by increasing the spatial layers of the actuator arrays. A low-cost DM prototype with 19 unimorph actuators located on three spatial layers is developed. The unimorph actuator can generate a wavefront deformation up to 11 µm at an operating voltage of 50 V. The DM can reconstruct typical low-order Zernike polynomial shapes accurately. The mirror can be flattened to 0.058 µm in RMS. Furthermore, a focal spot close to Airy spot is obtained in the far field after the aberrations of the adaptive optics testing system being corrected.

A Design Approach to Reducing Stress and Distortion Caused by Adhesive Assembly in Micromachined Deformable Mirrors

A common problem in deformable mirror assembly is that the adhesion of actuators to an optical mirror face sheet introduces unwanted topography due to large local stresses generated at the adhesive joint. A new approach to minimizing that effect is described, with inspiration taken from St. Venant’s principle, a fundamental precept in solid mechanics. It is demonstrated that moving the adhesive joint to the end of a slender post extending from the face sheet largely eliminates deformation due to adhesive stresses. A practical implementation of this design innovation is described, using silicon-on-insulator wafers and deep reactive ion etching. Simulation and experiments validate the effectiveness of the approach, reducing stress-induced topography on a test structure by a factor of 50. A prototype electromagnetic DM using this design approach is described, and its actuation is demonstrated. This new design can benefit a wide range of DMs that rely on actuator arrays that are adhesively bonded to a mirror face sheet.

A robotic honeycomb for interaction with a honeybee colony.

Robotic technologies have shown the capability to interact with living organisms and even to form integrated mixed societies composed of living and artificial agents. Biocompatible robots, incorporating sensing and actuation capable of generating and responding to relevant stimuli, can be a tool to study collective behaviors previously unattainable with traditional techniques. To investigate collective behaviors of the western honeybee (Apis mellifera), we designed a robotic system capable of observing and modulating the bee cluster using an array of thermal sensors and actuators. We initially integrated the system into a beehive populated with about 4000 bees for several months. The robotic system was able to observe the colony by continuously collecting spatiotemporal thermal profiles of the winter cluster. Furthermore, we found that our robotic device reliably modulated the superorganism's response to dynamic thermal stimulation, influencing its spatiotemporal reorganization. In addition, after identifying the thermal collapse of a colony, we used the robotic system in a "life-support" mode via its thermal actuators. Ultimately, we demonstrated a robotic device capable of autonomous closed-loop interaction with a cluster comprising thousands of individual bees. Such biohybrid societies open the door to investigation of collective behaviors that necessitate observing and interacting with the animals within a complete social context, as well as for potential applications in augmenting the survivability of these pollinators crucial to our ecosystems and our food supply.

Active Damping, Vibration Isolation, and Shape Control of Space Structures: A Tutorial

This tutorial reviews the author’s contributions to the active control of precision space structures over the past 35 years. It is based on the Santini lecture presented at the IAC-2022 Astronautical Congress in Paris in September 2022. The first part is devoted to the active damping of space trusses with an emphasis on robustness. Guaranteed stability is achieved by using decentralized collocated actuator–sensor pairs. The so-called integral force feedback (IFF) is simple, robust, and effective, and the performances can be predicted easily with simple formulae based on modal analyses. These predictions have been confirmed by numerous experiments. The damping strategy for trusses has been extended to cable structures, and also confirmed experimentally. The second part addresses the problem of vibration isolation: isolating a sensitive payload from the vibration induced by the spacecraft (i.e., the unbalanced mass of attitude control reaction wheels and gyros). A six-axis isolator based on a Gough–Stewart platform is discussed; once again, the approach emphasizes robustness. Two different solutions are presented: The first one (active isolation) uses a decentralized controller with collocated pairs of the actuator and force sensor, with IFF control. It is demonstrated that this special implementation of the skyhook, unlike the classical one, has guaranteed stability, even if the two substructures it connects are flexible (typical of large space structures). A second approach (passive) discusses an electromagnetic implementation of the relaxation isolator where the classical dash-pot of the linear damper is substituted by a Maxwell unit, leading to an asymptotic decay rate of −40 dB/decade, similar to the skyhook (although much simpler in terms of electronics). The third part of the lecture summarizes more recent work done on the control of flexible mirrors: (i) flat mirrors for adaptive optics (AO) controlled by an array of piezoelectric ceramic (PZT) actuators and (ii) spherical thin shell polymer reflectors controlled by an array of piezoelectric polymer actuators (PVDF-TrFE) aimed at being deployed in space.

Streamwise Extent and Ramp Rate Effects on Laminar Boundary Layer Response to Plasma Actuator Vortex Generators

AbstractThe unsteady output of a spanwise array of plasma actuators, arranged to generate streaks of high and low streamwise velocity in a Blasius boundary layer, is modeled numerically. When the forcing by the actuators undergoes a step change from off to on, the flow response downstream of the actuators is initially inverted in terms of the streamwise vorticity, disturbance velocity, and wall shear stress before approaching the steady-state behavior. The present study considers the effect of the length of the actuator in the streamwise direction and the effect of the rate change of the output of the actuator with respect to the nonminimum phase behavior. For the different rates of a gradually applied force, the body force increases linearly from zero to the same maximum value of the step, which simulates a reduced slew rate or ramped output. It is shown that the inverse flow response remains for the gradually applied input; however, the peak magnitude is less, and the overall response appears more damped. As the actuator length is reduced, while forcing was compensated for the shorter convective time over the actuator, the peak inverse response was enhanced.

Active nonreciprocal structural control on a flexible plate

Reciprocity is an acoustic property that describes the symmetry of sound transmission between two points. However, this property is undesirable in certain applications, and this has led to significant interest in the development of nonreciprocal acoustic devices that achieve one-way sound transmission. These devices typically achieve nonreciprocal sound transmission by introducing nonlinearities or directional biasing. Previously proposed nonreciprocal acoustic devices generally have limitations; for example, they may not be fully adaptable, they can introduce signal distortions such as additional harmonics, or they can only exhibit nonreciprocal behaviour over a narrow bandwidth. To overcome these challenges, previous work has demonstrated how an wave-based active control system can be used to drive an array of acoustic sources to achieve reversible and broadband non-reciprocal behaviour. This paper aims to extend this concept to a linear wave-based active structural-acoustic control system that uses an array of structural actuators to control the individual wave components to achieve broadband nonreciprocal transmission through a flexible plate in a three-dimensional environment. The performance of the wave-based active controller has been investigated at a range of incident angles and the limits of this controller have been identified.

Skin-integrated stretchable actuators toward skin-compatible haptic feedback and closed-loop human-machine interactions

Skin-integrated haptic interfaces that can relay a wealth of information from the machine to the human are of great interest. However, existing haptic devices are not yet able to produce haptic cues that are compatible with the skin. In this work, we present the stretchable soft actuators for haptic feedback, which can match the perception range, spatial resolution, and stretchability of the skin. Pressure-amplification structures are fabricated using a scalable self-assembly process to ensure an output pressure beyond the skin perception threshold. Due to the minimized device size, the actuator array can be fabricated with a sufficiently high spatial resolution, which makes the haptic device applicable for skin locations with the highest spatial acuity. A haptic feedback system is demonstrated by employing the developed soft actuators and highly sensitive pressure sensors. Two proof-of-concept applications are developed to illustrate the capability of transferring information related to surface textures and object shapes acquired at the robot side to the user side.

Alternating direction method of multipliers-based distributed control for distributed manipulation by shaping physical force fields

This paper proposes an algorithm for decomposing and possibly distributing an optimization problem that naturally emerges in distributed manipulation by shaping physical force fields through actuators distributed in space (arrays of actuators). One or several manipulated objects located in this field can “feel the force” and move simultaneously and independently. The control system has to produce commands for all actuators so that desired forces are developed at several prescribed places. This can be formulated as an optimization problem that has to be solved in every sampling period. Exploiting the structure of the optimization problem is crucial for platforms with many actuators and many manipulated objects, hence the goal of decomposing the huge optimization problem into several subproblems. Furthermore, if the platform is composed of interconnected actuator modules with computational capabilities, the decomposition can give guidance for the distribution of the computation to the modules. We propose an algorithm for decomposing/distributing the optimization problem using Alternating Direction Method of Multipliers (ADMM). The proposed algorithm is shown to converge to modest accuracy for various distributed platforms in a few iterations. We demonstrate our algorithm through numerical experiments corresponding to three physical experimental platforms for distributed manipulation using electric, magnetic, and pressure fields. Furthermore, we deploy and test it on real experimental platforms for distributed manipulation using an array of solenoids and ultrasonic transducers.

Effects of dual synthetic jets on longitudinal aerodynamic characteristics of a flying wing layout

A novel method of flight control based on dual synthetic jets (DSJ) is proposed and applied to a large-sweep flying wing aircraft with a hybrid flow mode of leading-edge vortex (LEV) and spanwise separation. An array of dual synthetic jet actuators (DSJAs) is placed along the leading edge to explore its aerodynamic control characteristics and control mechanism. The comparison with synthetic jets (SJ) is implemented to show the differences. Results show that DSJ could delay stalling angle of 6° and promote Cl with greater increments at large attack of angles (AOAs). At AOA of 36°, there was an obvious increase of 23.12% in Cl. Cd decreases at small AOAs, while augments sharply when AOA is larger than 26°. Nose-up moment could be improved. Above features indicate that leading-edge DSJ is not only a nice method of lift enhancement but also an efficient way of flight control. In the fuselage section, DSJ has functions of strengthening LEV, delaying the LEV breakdown and even regenerating LEV at large AOAs, which enhances the bleeding and improves the ability of resisting the reverse pressure gradient, thus totally suppressing the separation and forming the larger leading-edge suction. In the wing section, DSJ acts as a “LEV generator”. Reconstructed LEV could interact with the initial spanwise separation, emerging a hybrid flow mode of “streamers” and “rollers”, in which flow energy could be augmented and separation is partly suppressed. The comparison with SJ supports that the larger leading-edge suction and stronger LEV could be achieved by DSJ, which generate greater increments of Cl and Cm. Maximum Cl increments achieved by DSJ and SJ are respectively 23.12% and 16.91% of Cl without control, meaning DSJ has the higher applying potential in flight control with the same energy consumption.

Experimental Investigation and Intelligent Optimization of Airfoil Zero-Lift Drag Reduction with Plasma Actuators

Micro aerial vehicles flying at low speeds are becoming increasingly popular in military and daily life. Nevertheless, the short cruise time related to the poor aerodynamic efficiency of the wing at low Reynolds numbers is still a key issue. To deal with this, a spanwise plasma actuator array is used to reduce the zero-lift drag of a low-Reynolds-number airfoil, and experimental optimization of the electrical parameters is performed with intelligent algorithms. Results show that for efficient drag reduction, an unsteady unidirectional jet working mode should be preferred by the plasma actuator. In this mode, the drag reduction maps are mostly flat, and the drag reduction magnitude is insensitive to the variation of input voltage amplitude. There exists a threshold particle-observed Strouhal number (0.2) below which the drag reduction effectiveness drops sharply. As a comparison, the map of the power saving ratio shows a steep gradient, and its maximum always resides on the lower bound of duty cycle. With increasing freestream velocity, the mean drag reduction decreases monotonically. A genetic algorithm shows superior performance over surrogate-based optimization by reaching a maximum drag reduction of 40% and a peak power saving ratio of 0.7. Particle image velocimetry results reveal that there exists a laminar separation bubble on the airfoil. With plasma actuation, the transition location is shifted upstream, and the separation region is eliminated significantly. At low speeds, this pressure drag reduction exceeds the friction drag increase, resulting in a net drag decrease. However, transition-induced drag variation can only explain part of the total drag reduction, and the rest is inferred to be turbulent friction drag reduction.

Visualization study of perturbations induced by plasma actuators and its effect on shock wave/boundary-layer interaction

Surface arc plasma actuator array is used to control the shock wave/boundary-layer interaction in a Ma = 2 flow. Two types of interaction are examined. The flow topology of Surface arc plasma actuator array operating at high-frequency is firstly visualized via particle laser scattering (PLS) technique. The results show that two typical flow structures are observed in the discharging process: the thermal gas bubble and the trailing vortices. The high-frame low-exposure schlieren results for flow visualization indicate a significant separation inhibition in both experiments due to an improvement in the mixture upstream of the interaction region and promoting more turbulent structure into the boundary layer. In the baseline, the separation shock oscillates in a low-frequency mode. When plasma actuation is turned on, the spectra change dramatically when compared to the baseline condition without control. There is an apparent frequency shift for separation shock.Graphical abstract

Magnetomechanical Transport of Liquid Metal Droplets via Asymmetric Microwall Arrays

AbstractEutectic gallium indium liquid metal (LM) is a promising conductive liquid for various electronic applications. In particular, the directional transport of LM droplets has potential applications in soft electronics to control electrical conductivity. Existing methods transport LM droplets by applying an electric field to generate an interfacial tension difference within the LM droplet due to nonuniform ionic distribution of the electrical double layer. However, these methods require confined channels and tethered systems to apply the electric field. In this study, channel‐free wireless transport of LM droplets is demonstrated via on‐demand magnetomechanical actuation of asymmetric microwall arrays comprising vertically aligned ferromagnetic iron particles embedded in polydimethylsiloxane. Asymmetric microwall of two different widths is designed to generate an asymmetric bending stiffness at a given magnetic field. The asymmetric microwall bends gradually in response to a linear external magnetic field perpendicular to the alignment axis of the iron particles. Therefore, nonuniform magnetomechanical bending induces a local height gradient along the microwall, causing gravitational‐force‐driven roll‐off motion of the LM droplet. Transport direction of LM droplet is modulated by varying the geometric parameters. Finally, the opposite‐directional transport of two LM droplets is demonstrated under a linear magnetic field by pre‐programming the asymmetric bending direction of each microwall array.

Design and Feasibility Study of MRG-Based Variable Stiffness Soft Robot.

The conventional pneumatic soft robot has the problem of insufficient stiffness, while in the magnetorheological soft robot, the magnetic field provided by electromagnet has the disadvantage of oversized structure and poor flexibility. This paper presents a variable stiffness pneumatic soft robot based on magnetorheological grease (MRG) to solve these problems. Its three soft fingers cooperate with the adjustable gripper to adjust the gripping range for the robot hand, and it is used to provide gripping driving force through the bending drive. The MRG layer is designed on the gripping surface to provide adaptivity and rigid support for the gripped objects. A magnetic-air structure consisting of a Halbach array and Halbach array actuator is designed inside the soft fingers to provide a flexible magnetic field for the MRG layer. Theoretical and simulation analysis is carried out, and the results show that the state of the MRG changes and the stiffness of the clamping surface changes under the working pressure of 30 kPa. Finally, the experiment further proves the variable and high adaptivity of the surface stiffness of the gripping surface to reduce the damage to the gripped objects.

Nonlinear system stabilization in an anisotropic porous medium with Oldroyd-B fluid based on an actuator and sensor array

In this research, the authors precisely focus on the analysis of the chaotic behavior in an Oldroyd-B fluid saturated anisotropic porous medium via a feedback control technique. A four-dimensional (4D) weakly nonlinear system emerging from a Galerkin method of the constitutive and preservation equations is developed to accord with a convective stabilization with various Darcy numbers (Da) and feedback control gain value [Formula: see text]. The chaotic dynamic convection is governed by the Darcy–Rayleigh number ([Formula: see text]) and feedback control, while the Da has a significant impact on system stabilization. Their results reveal the effects of the feedback gain parameter [Formula: see text], stress relaxation parameter ([Formula: see text]), strain retardation parameter ([Formula: see text]), Darcy number (Da), mechanical ([Formula: see text]) and thermal ([Formula: see text]) anisotropy parameter on the stability and destabilization of thermal convection. Stabilization of thermal convection are important in cooling, nuclear power, and a range of technical, biological and engineering processes. In particular, feedback control gain values are discovered to be the preferred mode for the controlled onset of oscillatory convection. Finally, a graphical representation is presented to demonstrate that the feedback control approach is more effective in regulating the entire system when aperiodic external disturbances occur.

MRS-Tex: A Magnetically Responsive Soft Tactile Device for Texture Display

Tactile devices provide an intuitive way for texture display, which allows users to perceive the detailed surface properties of virtual or remote objects. For existing tactile devices that create actual topographical transformations, it remains challenging to render surface textures with high spatial resolution due to the limitation of the size of actuators. To address this challenge, a magnetically responsive soft actuator with a diameter of 1 mm is proposed. Integrating the high-density soft actuator array and a soft membrane bracket, we develop a magnetically responsive soft tactile device (named MRS-Tex) for texture display. When a magnetic field is applied, the magnetic units will sink to form pits, and the soft membrane bracket resists the finger pressure so that users can perceive the rendered surface texture. Thanks to the proposed sunken solution, MRS-Tex is capable of rendering surface textures with millimeter-level resolution (1.5 mm) while providing a sufficient upward holding force. Moreover, we conduct quantitative experiments and two user studies to evaluate the performance of MRS-Tex. Experimental results show that MRS-Tex can generate pits with a depth of more than 0.20 mm, which is sufficient for rendering perceivable surface textures. The average discrimination accuracy of user study can reach up to 82% for both six basic texture patterns and four complex texture patterns.