Actuation Techniques Research Articles

A Single-Chamber Pneumatic Soft Bending Actuator With Increased Stroke-Range by Local Electric Guidance

Thanks to their continuously deformable features, soft bending actuators, including pneumatic and electric actuators, are increasingly used in continuum robots. Further development, however, is limited by the complexity of the multicavity structure in pneumatic actuators and the instability of the electromechanical coupling in dielectric elastomer actuators. In this article, by combining the advantages of the two actuation techniques, a novel hybrid electro-pneumatic bending actuator is proposed that is capable of bending with significantly reduced complexity and improved stability. A timing control method is proposed that enables rapid and significant bending. A low voltage is used for bending guidance with air-pressure concurrently to produce a large bending stroke. The results of experiments indicate that, with increasing air pressure, the bending angle varies in three different stages. These stages are (I) a low-pressure guidance stage, (II) an instability induction stage, and (III) a stable deformation stage. By harnessing the instability at stage II, the driving voltage can be substantially reduced to avoid electric breakdown. By studying the effect of prestretch on bending, the controllability of the bending deformation is improved. The simulation is also used to verify the control method and predict the development path of soft robots.

Haptic Training Simulation

Immersive virtual environments combined with haptic (kinaesthetic and/or tactile) feedback are becoming an essential building block of simulator training in a variety of applications. This paper aims to illustrate the interest of hands-on training simulation with haptic feedback. We review the recent application domains and we expose the progress and open challenges in the medical domain which is particularly demonstrative. The paper then addresses two aspects of haptic feedback that could help enhance modern haptic training simulators' performance, namely transparent and efficient actuation for kinaesthetic feedback and tactile feedback. This research topic, beyond technological progress, should help design kinaesthetic and tactile haptic interfaces and motivate the use of new actuation techniques for more realistic and effective feedback in simulations as soon as users are immersed in virtual environments.

Drag Reduction and Energy Saving by Spanwise Traveling Transversal Surface Waves for Flat Plate Flow

Wall-resolved large-eddy simulations are performed to study the impact of spanwise traveling transversal surface waves in zero-pressure gradient turbulent boundary layer flow.Eighty variations of wavelength, period, and amplitude of the space- and time-dependent sinusoidal wall motion are considered for a boundary layer at a momentum thickness based Reynolds number of {rm Re}_theta = 1000. The results show a strong decrease of friction drag of up to 26% and considerable net power saving of up to 10%. However, the highest net power saving does not occur at the maximum drag reduction. The drag reduction is modeled as a function of the actuation parameters by support vector regression using the LES data.A dependence of the spanwise pressure drag on the wavelength is found. A substantial attenuation of the near-wall turbulence intensity and especially a weakening of the near-wall velocity streaks are observed. Similarities between the current actuation technique and the method of a spanwise oscillating wall without any normal surface deflection are reported. In particular, the generation of a directional spanwise oscillating Stokes layer is found to be related to skin-friction reduction.

A review on Aerodynamic performance of NACA Airfoil for various Reynolds number

Morphing and shape shifting technologies offer a wide range of applications in airplane design and are complicated to operate effectively with current existing methods. Variable camber wings is a innovative control surface technology designed as aero elastic wing shaping control device which minimizes drag throughout its flight envelope and increases performance in different flight conditions which leads to corresponding increase in airplane flight efficiency. In order to achieve these results one has to rely on different flight actuator configurations and techniques to achieve variable camber mechanism. Variable camber can be achieved span vice or chord wise on an aerofoil where a slight variation in thickness changes lift coefficient. Variable camber wing is a flexible structure that changes its shape profile at different aerodynamic load these types of wings are tested under different load conditions and Reynolds number in wind tunnel facility to have a detailed study on the performance. In this paper an attempt has been made to cover all the shape shifting and morphing wing technologies and compare the results and discuss the possibility of adaption of such technology in aerospace industry.

Novel Emerging Sensing, Actuation, and Control Techniques for Haptic Interaction and Teleoperation

Haptics is a field of study that deals with perceiving, transmitting, and reproducing human haptic sense. Auditory and visual sensations are unilateral, whereas haptic sensation is bilateral via the principle of action and reaction. Haptic technologies have been applied, with ever increasing potential, in manufacturing, medicine, entertainment, and defense.

A review of magnetic actuation systems and magnetically actuated guidewire- and catheter-based microrobots for vascular interventions

Magnetic actuation techniques and microrobots have attracted considerable interest due to their potential applications in biomedicine. Interventional techniques have emerged as a minimally invasive approach to treat a wide range of vascular diseases. The current practice of interventional procedures is, however, limited by manual control of interventional devices and time-consuming procedures. Moreover, fluoroscopy is considered as an essential part of the procedure today despite posing many limitations for patients and physicians. Recently, various microrobotic solutions have been proposed for vascular interventions, including advances in magnetic navigation systems and magnetically steerable catheters and guidewires, which have shown potential benefits such as reduced radiation doses, improved access to difficult-to-reach and tortuous anatomy. This paper reviews the commercial magnetic actuation systems and magnetically actuated interventional microrobots that have been developed by academic research groups and medical companies worldwide, outlining their capability, applicability as well as limitations. We further address the challenges and future prospects of the research toward clinical acceptance of magnetic interventional technologies.

Reconfigurable Real-Time Power Grid Emulator for Systems With High Penetration of Renewables

Novel power system control and new utility devices need to be tested before their actual deployment to the power grid. To assist with such a testing need, real-time digital emulators such as RTDS and Opal-RT can be used to connect to the physical world and form a hardware in the loop (HIL) emulation. However, due to the limitations of today’s computational resources, the accuracy and fidelity suffer from different levels of model reductions in purely digital simulations. CURENT has developed a reconfigurable electric grid hardware testbed (HTB) to overcome the limitations of digital emulators. The HTB has been used to develop measurement, control, modeling, and actuation techniques for a national grid with a high penetration of renewables. The power electronic-based system includes emulators for synchronous generators; photovoltaics with grid-interfacing inverter; wind turbines; induction motor loads, ZIP loads, power electronic loads; batteries; ac and dc transmission lines; short circuit faults and grid relay protection; and a multiterminal HVDC overlay including power electronics interfaces. The system contains real elements of power flow, measurement, communication, protection, and control that mimic what would be seen in an actual electric grid. This paper presents an overview of the HTB and several scenarios that have been run to determine control and actions needed for the future power grid.

Liquid-Metal Nodal Sheet for Reconfigurable Devices and Circuits

Gallium-based liquid metals have attracted attention as a conductive adaptable material that can be shaped to obtain reconfigurability. We demonstrate a two-dimensional array of liquid-metal conductive nodes, in which reconfigurability is achieved by merging and splitting adjacent nodes to reversibly shape a two-dimensional structure. The nodes are reconfigured using three different actuation schemes: 1) pressure-point actuation, where the liquid metal is actuated by pressing on the flexible superstrate; 2) surface-tension self-splitting, where the geometric shape of the node itself exerts a separating force on merged nodes; and 3) electrocapillary actuation where the liquid metal is actuated by a DC electrical signal. This is the first demonstration of a reconfigurable liquid-metal pixel array using liquid-liquid interconnects for prototyping reconfigurable devices. As a proof of concept, the proposed actuation techniques are used to reconfigure a liquid-metal nodal patch antenna, in which the liquid-metal nodes are reversibly connected and disconnected to change the operating frequency and polarization.

Resonance frequency selective electromagnetic actuation for high-resolution vibrotactile displays

Vibrotactile displays offer significant potential for conveying information through the sense of touch in a wide variety of applications. Spatial resolution of these displays is limited by the large size of actuators. We present a new selective electromagnetic actuation technique to control the vibrations of multiple tactile elements using a single coil based on their individual mechanical resonance frequencies. This technique allows low-cost and highly reliable implementation of many tactile elements on a smaller area. A prototype is manufactured using 3D-printed tactile elements and off-the-shelf coils to characterize the proposed technique. This prototype successfully increases the resolution by 100 % from 16 to 32 tactile pixels (taxels) on a 25 cm2 pad, without sacrificing other performance metrics such as refresh rates and power consumption. The multiphysics finite element analysis developed for this new actuation technique are experimentally validated by optical vibrometry measurements. This work demonstrates the capability of resonance-selective electromagnetic actuator in developing high-resolution low-cost vibrotactile displays.

Optical control and manipulation of diamagnetically levitated pyrolytic graphite

When levitating above an alternating-pole permanent magnet array, pyrolytic graphite can be displaced by asymmetric diamagnetic forces resulting from optically-induced, localized temperature changes and the thermal dependence of pyrolytic graphite’s magnetic susceptibility. In this paper, we present methods for addressable, automated position control of levitating pyrolytic graphite samples acting as milli-robots for small-scale assembly and manipulation applications using optical actuation and machine vision techniques. A simple control method is presented that harnesses interactions between complex magnetic fields and small-scale thermomagnetic and optical material properties. A user may dictate arbitrary desired milli-robot positions to a closed loop control system, which automatically detects and actuates milli-robots to the desired positions and works to maintain them there. Hardware requirements and considerations are discussed along with software calibration, image processing, and control methodologies. Results from experiments demonstrating automated position control of pyrolytic graphite milli-robots of various sizes levitating over various permanent magnet array configurations are presented. Sequential control of multiple milli-robots in close proximity without work surface segmentation is also demonstrated successfully. The observed effect of milli-robot size to magnet array grid spacing ratio on milli-robot in-plane motion is discussed, concluding that larger ratios result in smoother and faster motion control due to relative decreases in magnetic barrier forces on the pyrolytic graphite milli-robot and minimized separation between minimum free energy positions.

An Overview of Piezoelectric Self-Sensing Actuation for Nanopositioning Applications: Electrical Circuits, Displacement, and Force Estimation

The industrial sector often employs piezoelectric materials as actuators for a variety of uses, some of which require a precise positioning while being limited by space and cost factors that impede the insertion of external position and force sensors. Piezoelectric actuators (PEAs) are characterized by strong nonlinearities (hysteresis and creep), badly damped oscillations, and sensitivity to the environment, especially temperature variation, which makes the measurement of the position mandatory to guarantee the required precision and repeatability of piezoelectric-based positioning systems operating at the microscale and nanoscale. Self-sensing actuation (SSA) techniques allow the implementation of precise positioning control of PEAs without the hindrance of external position sensors. This article reviews the different SSA techniques used for precise positioning control of PEAs. The principle of SSA is defined by the capability of deriving the physical state of a PEA (displacement, perceived force, and so on) without the use of external sensors to directly measure thereof, but rather by estimating it from the measurement of less intrusive and cheaper physical signals produced by the PEA itself (throughout current, voltage drop, and so on). The applicability and constraints of each SSA approach are examined in order to help in the determination of the most adequate approach for precise control of PEAs positioning and handling force control.

Methodology of Exoskeleton with Actuation Methods and Discussion of Nerves sensing for Exoskeleton

Background/objectives: As the use of rehabilitation exoskeletons (techniques) has become an important means of treatment of stroke patients. This study has discussed different actuator methodologies and techniques that can be used in a movement of the exoskeleton and proposed design of exoskeleton with enhanced efficiency. Methods/statistical analysis: After reviewing several actuation techniques and analyzing various products available in the market, a less complex easy functioning design of exoskeleton is proposed with improved performance and lifetime, which can able to detect the signal directly from the nerve system with the help of EMG sensors and command the actuator after processing of the signal for the required movement. Findings: Mainly there are two major contributors sensing and actuation technique that is responsible for the efficient working of the exoskeleton. There are such types of sensors available which can fetch data or signal directly from the nerve system of the human body. Tremendous work is going on to make the actuators less complex, handy and easy working in order to improve the quality of the exoskeleton. Again some of the conventional exoskeleton based on string and motor system is not appropriately performing. The electric linear actuation system is a better solution in order to make the exoskeleton more qualitative nowadays as compared to others. Improvements/ applications: Exoskeleton is helpful for the person with a disability in terms of movement and reduced their dependency on others. These devices are used to make a disabled person walking, running, jumping and do any other movementrelated work without any help. Keywords: Exoskeleton, Sensor, Actuator, Nerve Impulse

Characteristic measurement of a surface acoustic wave nano-stepping motor by using a fiber-optic Michelson interferometer

The actuation technique of a surface acoustic wave motor with nanometer scale linear motion was experimentally investigated in this study. The surface acoustic wave motor comprised a stator made of a Y+128° cut, X-propagation lithium niobate substrate with silicon sliders and an array of pillar projections manufactured using semiconductor fabrication techniques. Two sets of interdigital transducers deposited on the substrate were used to generate Rayleigh waves with a driving frequency of up to 9.7 MHz. The surface acoustic wave motor was driven by friction exerted on the contact area between the slider and the surface acoustic waves in a retrogressive elliptical locus. The stepping motion of the surface acoustic wave motor was measured directly using a fiber-optic Michelson interferometer through demodulation with a digital signal processing method. A displacement of several nanometers was achieved at each step during the experiment.

A virtual actuator approach for the secure control of networked LPV systems under pulse-width modulated DoS attacks

In this paper, we formulate and analyze the problem of secure control in the context of networked linear parameter varying (LPV) systems. We consider an energy-constrained, pulse-width modulated (PWM) jammer, which corrupts the control communication channel by performing a denial-of-service (DoS) attack. In particular, the malicious attacker is able to erase the data sent to one or more actuators. In order to achieve secure control, we propose a virtual actuator technique under the assumption that the behavior of the attacker has been identified. The main advantage brought by this technique is that the existing components in the control system can be maintained without need of retuning them, since the virtual actuator will perform a reconfiguration of the plant, hiding the attack from the controller point of view. Using Lyapunov-based results that take into account the possible behavior of the attacker, design conditions for calculating the virtual actuators gains are obtained. A numerical example is used to illustrate the proposed secure control strategy.

Liquid actuated gravity experiments

We describe a new actuation technique for gravity experiments based on a liquid field mass. The characterizing idea is to modulate the gravity force acting on a test mass by controlling the level of a liquid in a suitable container. This allows to obtain a periodical gravity force without moving parts (except the liquid level) close to the TM. We describe in detail the most relevant aspects of the liquid actuator and discuss how it can be used in gravity experiments. In particular, we analyze an application to test the inverse square law in the mm to cm distance region.

Review on Switches for Power Applications: Macro to Micro

Background: Switches are important component in electrical system. The switches needs to have the advantages of low ON-state resistance, very high OFF-state resistance, high isolation, no leakage current, less power loss, fast switching, high linearity, small size, arcless and low cost in bulk production. Also these switches have to be reliable and environmental friendly. Methods: In this paper, macro and microswitches for power applications are extensively reviewed and summarized. Various types of switches such as mechanical, solid-state, hybrid and micromechanical switches have been used for power applications are reviewed. The importance and challenge in achieving arcless switching is presented. Results: The use of micromechanical switches for power applications, actuation techniques, switching modes, reliability and lifetime are also reviewed. The modeling and design challenges are also reviewed. Conclusion: The applications of micromechanical switches shows that the switches can reduce the leakage current in battery operated systems and reduce the size of the system considerably.

Optical gradient force for tuning, actuation, and manipulation of nonlinearity in graphene nanomechanical resonator

Graphene nano-mechanical resonators integrated over waveguides provide a powerful sensing platform based on the interaction of graphene with the evanescent wave. An integrated actuation scheme that does not compromise this interaction is required for optimal usage of the ultra-sensitive platform. Conventional electrical and optical actuation techniques are not favorable towards efficient utilization of the near-field interaction. We propose tuning and actuation of these resonators using on-chip optical gradient force due to the guided wave as an alternative to these conventional techniques. We have used the fundamental quasi-TM optical mode in a silicon waveguide in a finite-element model. We obtain a force–distribution that is spatially correlated with the fundamental mechanical mode of the graphene nano-mechanical resonator. We demonstrate that for an evanescent continuous-wave (CW) optical power of 8 μW, the resonant frequency of the device can be tuned by about 24.5%. With an intensity-modulated optical power ≤0.1 μW, the mechanical mode can be driven to nonlinearity. We also demonstrate cancellation of the Duffing nonlinearity at a CW power of 5.4 μW, which can be used to improve the linear dynamic range of vibration. The distributed optical gradient force can produce linear resonant amplitudes that are 50% higher than those obtained using conventional actuation schemes. This actuation scheme is robust against fluctuations in the evanescent optical power and in the refractive index of the side-cladding of the waveguide. This ensures minimal cross-talk from the optical mode to the mechanical mode in nano-mechanical sensing applications.

Passive microinjection within high-throughput microfluidics for controlled actuation of droplets and cells

Microinjection is an effective actuation technique used for precise delivery of molecules and cells into droplets or controlled delivery of genes, molecules, proteins, and viruses into single cells. Several microinjection techniques have been developed for actuating droplets and cells. However, they are still time-consuming, have shown limited success, and are not compatible with the needs of high-throughput (HT) serial microinjection. We present a new passive microinjection technique relying on pressure-driven fluid flow and pulsative flow patterns within an HT droplet microfluidic system to produce serial droplets and manage rapid and highly controlled microinjection into droplets. A microneedle is secured within the injection station to confine droplets during the microinjection. The confinement of droplets on the injection station prevents their movement or deformation during the injection process. Three-dimensional (3D) computational analysis is developed and validated to model the dynamics of multiphase flows during the emulsion generation. We investigate the influence of pulsative flows, microneedle parameters and synchronization on the efficacy of microinjection. Finally, the feasibility of implementing our microinjection model is examined experimentally. This technique can be used for tissue engineering, cells actuation and drug discovery as well as developing new strategies for drug delivery.

High-Bandwidth 3-D Multitrap Actuation Technique for 6-DoF Real-Time Control of Optical Robots

Optical robots are microscale structures actuated using laser trapping techniques. However, the lack of robust and real-time three-dimensional (3-D) actuation techniques reduces most applications to planar space. We present here a new approach to generate and control several optical traps synchronously in 3-D with low latency and high bandwidth (up to 200 Hz). This time-shared technique uses only mirrors, hence, is aberration free. Simultaneous traps are used to actuate optical robots and provide 6-DoF telemanipulation. Experiments demonstrate the flexibility and dexterity of the implemented user control, paving the way to novel applications in microrobotics and biology.

Droplet actuation on superhydrophobic substrates via electric field gradients

A superhydrophobic surface is non-sticking to aqueous droplets due to minimized solid-liquid contact, but the small contact area also poses challenges to droplet maneuvering. This letter reports a technique using electric field gradients to actuate aqueous droplets on superhydrophobic surfaces. A pin-ring electrode pair underneath the insulating superhydrophobic surface is used to generate electric field gradient above the surface, with the field focused around the pin. The non-uniform field operates on the electrostatically induced charges on the droplet, producing an actuation force attracting the droplet toward the pin. The actuation force is proportional to the square of the imposed field as shown in both experiments and simulations. This non-contact actuation technique is effective in electrostatically trapping and translating superhydrophobic droplets, despite the small solid-liquid contact. The pin-ring configuration can be readily extended to a pin array between two parallel lines, which essentially form a stretched ring closing at infinity. The pin array is used to demonstrate individual actuation of two droplets leading to their eventual coalescence.