Actuation Time Research Articles

Powering reversible actuators using forward osmosis membranes: feasibility study and modeling

ABSTRACTThe aim was to determine the impact of membrane properties and operating conditions upon predicted performance of osmotically driven actuators. An actuator fitted with a forward osmosis membrane was studied, and significantly we examined the reversibility of the actuation process. It was discovered that the actuation-retraction cycle could be repeated for over 60 cycles before salt concentration became similar on both sides of the membrane. The cycle length and number of operative cycles were shown to be a dependent on membrane properties. It was demonstrated that issue of long actuation time can be addressed using membranes with high water permeability.

A Model for Measurement of the Electromagnetic Parameters of Relays in Diagnostics System

A model for measurement of objects of testing that have a long duration is considered. The model comprises a sequence of operations that need to be performed on the object of testing to measure actuation or release voltages. At the first stage, test controls with various parameters are launched in the model to determine preliminary points based on which the dependence of actuation or release voltage changing is constructed. The value of the control signal is then substituted for this dependence, and the desired voltage actuation or release is derived. The model construction is based on the use of series. The form of the support function is chosen, all the terms of this transcendental function are found, the left side of the function contains preliminarily obtained results of the effects of the test control signals, and the desired coefficients and control signals are on its right side. The form of transcendental functions as fractionally rational series is defined in the model, since it is best to construct the dependence shape using these functional series. The solution of the support function is based on matrix computation using the Gaussian method for normal and overdetermined systems and the Cauchy theorem for multiplication of polynomials. The implementation of the model made it possible to halve the measuring time of actuation and release voltages compared with the commonly used testing technique of a relay of the first class of reliability.

Vehicle actuated signal performance under general traffic at an isolated intersection

We study green extension of a two-phased vehicle actuated signal at an isolated intersection between two one-way streets. The green phase is extended by a preset time interval, referred to as critical gap, from the time of a vehicle actuation at an advance detector. The green phase switches if there is no arrival during the critical gap. We develop an exact model to study the intersection performance with traffic following Poisson processes. We further extend the model to approximate the case of general traffic. Our model in the general case works well compared with Monte Carlo simulation. A few major observations include: (1) The optimal critical gap decreases with the traffic; (2) The optimal critical gap can be much larger (up to 5 s) than the common presumption of 2–3 s; (3) Queue clearance policy is not nearly optimal in general even in the case of heavy traffic.

Microfluidically Reconfigurable Reflection Phase Shifter

A microfluidic-based reconfiguration approach is presented for realizing a reflection phase shifter. The phase shifter consists of quadrature hybrid coupler with reflective microstrip line terminations. A selectively metallized plate (SMP) that can be repositioned inside a microfluidic channel is brought in close proximity ( $\mu \text{m}$ ) of the reflective microstrip line terminations to vary their electrical lengths through capacitive RF short mechanism. The concept is demonstrated through a 9.5 GHz $X$ -band phase-shifter design. Specifically, the design exhibits a footprint of $24\times15$ mm2, operates with <0.95 dB insertion loss, and attains the 360° phase shift with a total of 9.5 mm SMP motion resulting in 1.95 s total actuation time with the selected external micropumps. These phase shifters may be suitable for applications that prioritize low-loss and high power handling capability over reconfiguration speed.

Scalable static droplet array for biochemical assays based on concentration gradients

Many important biological assays demand rapid and low-cost screening systems. In this study, we present a scalable static droplet array (SDA) that can generate a high-resolution concentration gradient. The system consists of discrete sample dispensing channels, array units, and microvalves for droplet generation and droplet storage. We utilize negative pressure on a suction valve located below array chambers to enhance the capacity of droplet filling. The size of the droplets is controlled by valve actuation time, and array chambers can contain up to 32 droplets with a 20-millisecond valve actuation time. We present various profiles of concentration gradients generated by the combined storage of binary concentrations of droplets. As a proof of concept, we performed an enzymatic inhibition assay for validating our system with IC50 and the Hill coefficient using β–galactosidase (β-gal), di(β-d-galactopyranoside) (FDG) and 2-Phenylethyl β-d-thiogalactoside (PETG), and achieved an IC50 value of 2.18 μM and a Hill coefficient of 1.11, which agrees well with results in the literature. We anticipate that this system will serve as a general assay platform that is capable of high-throughput screening for various biological assays and imaging.

3D manufactured, water-powered soft actuators for orthodontic application

Soft actuators with embedded power sources are critical for applications where space is limited but safety and functionality are demanded. We have successfully demonstrated (1) a 3D design/fabrication/packaging scheme that can readily upgrade conventional hydraulic actuators into autonomous osmotic actuators, and (2) integrated soft actuators that can yield desired locomotion and force outputs for orthodontic application. Flexible composite structures with semipermeable interfaces are employed to realize the desired actuation, including elongation, contraction, bending, and twisting. More specifically, thin-walled polymer bellows are utilized to control and amplify the actuation caused by osmosis. In the prototype demonstration, 25 mm long soft bellow structures with outer diameters up to 4 mm and wall thicknesses down to 250 μm were designed, 3D printed, shrink wrapped with semipermeable membranes, assembled, and characterized. When placed in aqueous media, the actuators were osmotically pressurized to function in steady and preprogrammed manners. The constant water flow rate across the semipermeable interface (with an effective working area of 30 mm2) into each presented osmotic actuator was measured to be 156 μl h−1, while the inner pressure can reach 200 kPa in few hours. It was demonstrated that both the inner/outer pressure difference and locomotion/force outputs are proportional to the actuation time. When applied on teeth, the osmotic actuators are expected to steadily overcome the rising resistance from surrounding tissues, and therefore achieve constant-rate and long-lasting movement of teeth. In addition to pumping, it is demonstrated for the first time that osmotic actuation can be tailored to accomplish sophisticated locomotion functions.

Testing of Coiled Nylon Actuators for Use in Spastic Hand Exoskeletons.

Natural muscles have many favorable characteristics including their high power-to-weight ratio, efficient energy conversion and fast actuation times. These factors become important criteria for judging artificial actuation methods. Unfortunately, traditional systems such as pneumatic and electromagnetic motors have yet to attain similar characteristics. In recent years, a new category of actuators has been developed from highly twisted and coiled low-cost nylon fibers. These muscles are capable of providing a powerful stroke per cycle with a reversible contraction. In this paper, twisted and coiled polymer (TCP) actuators with two different commercially available nylon fibers: Shieldex conductive yarn 117/17 and 235/34 are fabricated and tested, then implemented into a low profile, hand exoskeleton. Maintaining quality control on muscle fabrication proved to be challenging and the use of nylon as muscle actuators for exoskeletons would require much more research and better measurements of critical parameters before providing a consistent solution.

Flow separation control by dielectric barrier discharge plasma actuation via pulsed momentum injection

Control of a turbulent boundary layer separating on a half-cylinder mounted on a flat plate has been investigated using a Dielectric Barrier Discharge (DBD) plasma actuator placed along the apex of a cylinder. The main focus of the study has been to evaluate if the control ability of the actuator can be improved through pulsed actuation compared to its steady counterpart. Investigations of the electric wind induced by the DBD plasma actuator in still air, when mounted on the flat plate, revealed that while the steady actuation produces an electric wind similar to a wall jet, the pulsed actuation creates a train of co-rotating vortices. The vortices are the result of a starting vortex produced by the actuator at each actuation pulse. A parametric study showed a dependence of the size, shape and propagation velocity of the vortices on the pulse frequency and duty cycle. With the actuator mounted along the apex of the cylinder, Particle Image Velocimetry measurements of the uncontrolled and controlled flow with a free-stream velocity of 5 m/s showed a clear reduction of the recirculation region downstream the cylinder when using plasma actuation. An even higher control effect could be achieved with pulsed actuation compared to the steady actuation. Phase-locked measurements of the unsteady actuation showed that pulsed actuation periodically shifted the flow separation location resulting in the propagation of vortical structures in the recirculation region. The size of the vortical structures showed a dependence on the pulsed actuation timing parameters.

Machine Vision Retrofit System for Mechanical Weed Control in Precision Agriculture Applications

This paper presents a machine vision retrofit system designed for upgrading used tractors to allow the control of the tillage implements and enable real-time field operation. The retrofit package comprises an acquisition system placed in the cabin, a front-mounted RGB camera sensor, and a rear-mounted Peiseler encoder wheel. The method combines shape analysis and colorimetric k-nearest neighbor (k-NN) clustering for in-field weed discrimination. This low-cost retrofit package can use interchangeable sensors, supplying flexibility of use with different farming implements. Field tests were conducted within lettuce and broccoli crops to develop the image analysis system for the autonomous control of an intra-row hoeing implement. The performance showed by the system in the trials was judged in terms of accuracy and speed. The system was capable of discriminating weed plants from crop with few errors, achieving a fairly high performance, given the severe degree of weed infestation encountered. The actuation time for image processing, currently implemented in MATLAB integrated with the retrofit kit, was about 7 s. The correct detection rate was higher for lettuce (from 69% to 96%) than for broccoli (from 65% to 79%), also considering the negative effect of shadows. To be implementable, the experimental code needs to be optimized to reduce acquisition and processing times. A software utility was developed in Java to reach a processing time of two images per second.

High-speed and high-efficiency shape memory alloy actuation

When standard voltage levels commonly adopted in industry are used to activate thermal shape memory alloy (SMA) wire actuators, they often result in very high electrical currents which may eventually damage or destroy the actuators. To improve performance of SMA wire actuators operating in industrial environments, in this paper we investigate a novel, fast and energy-efficient actuation strategy based on short pulses in the millisecond range. The use of higher voltages leads to a highly dynamic activation process, in contrast to commonly used quasi-static activation based on low-voltage. A test setup is designed to examine the effects of the control parameters (i.e., supply voltage, activation pulse duration, SMA wire pre-tension and wire diameter) on the measured displacement and force output of the SMA wire. It is shown that actuation times in the range of 20 ms and strokes of more than 10% of the SMA wire length can be reached. Additionally, energy savings of up to 80% with respect to conventional quasi-static actuation are achieved. Possible applications for this activation method are release mechanisms, switches or safety applications.

Motion control in free-standing shape-memory actuators

In this work, free-standing shape-memory thermally triggered actuators are developed by laminating ‘thiol-epoxy’-based glassy thermoset (GT) and stretched liquid-crystalline network (LCN) films. A sequential curing process was used to obtain GTs with tailored thermomechanical properties and network relaxation dynamics, and also to assemble the final actuator. The actuation extent, rate and time were studied by varying the GT and the heating rate in thermo-actuation with an experimental approach. The results demonstrate that it is possible to tailor the actuation rate and time by designing GT materials with a glass transition temperature close to that of the liquid-crystalline-to-isotropic phase transition of the LCN, thus making it possible to couple the two processes. Such coupling is also possible in rapid heating processes even when the glass transition temperature of the GT is clearly lower than the isotropization temperature of the LCN, depending on the network relaxation dynamics of the GT and the presence of thermal gradients within the actuators. Interestingly, varying the GT network relaxation dynamics does not affect the actuation extent. As predicted by the analytical model developed in our previous work, the modulus of the GT layer is mainly responsible for the actuation extent. Finally, to demonstrate the enhanced control of the actuation, specifically designed actuators were assembled in a three-dimensional actuating device able to make complex motions (including ‘S-type’ bending). This approach makes it possible to engineer advanced functional materials for application in self-adaptable structures and soft robotics.

Electrowetting actuated liquid prism with large steering angle based on additional gravitational effects

AbstractIn this paper, we propose a liquid prism based on electrowetting‐on‐dielectric and gravity effect. The device is filled with two immiscible liquids. The conductive liquid is filled in the upper part of the device, and the oil is filled in the bottom of the device. Different from the conventional liquid prism, the density of the conductive liquid is larger than that of the oil. The liquid–liquid interface can form a tilt shape when applied different voltages to the opposite sidewalls. The beam will be deflected when the light passes through the device. Our results show that the tilt angle of the liquid–liquid interface is ~45°, and the light beam can be deflected by 22.2° (−10.9° to +11.3°). The actuation time of the device is ~240 ms. The proposed liquid prism for light beam steering and tracking has potential application in laser directions, telecommunications, and scanners.

Using experimental sprinkler actuation times to assess the performance of Fire Dynamics Simulator

This article considers the predictive capabilities of Fire Dynamics Simulator for sprinkler actuation time when benchmarked against data from a series of 22 enclosure experiments. Sensitivity analyses have been undertaken for grid size, conductivity factor, radiative fraction and enclosure leakage areas. ‘Goodness of fit’ calculations indicate that Fire Dynamics Simulator is able to provide an average prediction of sprinkler actuation time within a Euclidean relative difference of 0.18. Comparisons to results determined in previous studies, using different modelling methods and Fire Dynamics Simulator versions, have also been made. The sensitivity analyses and comparisons indicate the importance of the decisions made by the modeller in representing fire scenarios, even when modelling ‘simple’ experiments where data for inputs such as the heat release rate, geometry and sprinkler characteristics are available. The comparisons therefore indicate that with the reduced degrees of freedom compared to other modelling studies, there is still potential for a range of assumptions and simulation results.

Robust control of an active suspension system with actuator time delay by predictor feedback

In this study, a delay-dependent memory state-feedback controller for linear systems with input time-delay in the presence of external disturbance has been investigated. At first, a new formula is introduced to obtain the prediction vector from the system dynamics and then by using this formula, the effect of input time-delay on the original delayed system is reduced. To guarantee the prescribed disturbance attenuation level of the closed-loop system, Lyapunov theory and linear matrix inequality (LMI) approaches are used. In the case of feasibility, sufficient LMI conditions provide the stabilising gain of the predictor-based controller. To illustrate the effectiveness of the proposed method, it is applied to a quarter-car model of an active suspension system considering the actuator time-delay.

Analysis of PWR SBO sequences with RCP passive thermal shutdown seals

ABSTRACT The operation of recently implanted low-leakage seals after Fukushima has altered the analysis of classical PWR Station Blackout (SBO) sequences , as Seal Loss of Coolant Accident (SLOCA) is no longer one of the dominant factors in the accident progression . An analysis of different management strategies in non-SLOCA sequences has been performed by means of the Integrated Safety Assessment (ISA) methodology using the SCAIS-MAAP model of a 3-Loop PWR Westinghouse design. Through the use of the Damage Domain concept(i.e. the region of the uncertain crew actuation times or physical parameters space where each damage limit is exceeded for each sequence), the times for reaching different damage limits are obtained. Results evidence the positive impact of low-leakage seals, which greatly increase the margin to core uncoveryand reduce core damage frequency. Results also allow concluding that an SBO is dominated, namely by the Auxiliary Feed-Water (AFW) mass flow(turning blind AFW management into an essential procedure), SLOCA (in case the new low-leakage seals fail or they are not present), an excessive AFW mass flow (leading to Turbine-Driven Pump failure) and the DC failure time (losing control valves and the instrumentation).

Estimation of Neuromuscular Primitives from EEG Slow Cortical Potentials in Incomplete Spinal Cord Injury Individuals for a New Class of Brain-Machine Interfaces.

One of the current challenges in human motor rehabilitation is the robust application of Brain-Machine Interfaces to assistive technologies such as powered lower limb exoskeletons. Reliable decoding of motor intentions and accurate timing of the robotic device actuation is fundamental to optimally enhance the patient's functional improvement. Several studies show that it may be possible to extract motor intentions from electroencephalographic (EEG) signals. These findings, although notable, suggests that current techniques are still far from being systematically applied to an accurate real-time control of rehabilitation or assistive devices. Here we propose the estimation of spinal primitives of multi-muscle control from EEG, using electromyography (EMG) dimensionality reduction as a solution to increase the robustness of the method. We successfully apply this methodology, both to healthy and incomplete spinal cord injury (SCI) patients, to identify muscle contraction during periodical knee extension from the EEG. We then introduce a novel performance metric, which accurately evaluates muscle primitive activations.

Universal Transient Dynamics of Electrowetting Droplets

Droplet spreading on substrates by electrowetting exhibits either of the two transient behaviours: one characterised by contact line oscillation, and the other one by slow spreading dynamics. The transition between these behaviours remains elusive due to the current limited understanding of the spreading dynamics on the hydrodynamical and electrical properties of electrowetting systems. To understand this transition we propose a model capturing the transition’s occurrence based on both the hydrodynamical and electrical parameters. We derive the critical viscosity at which the transition occurs and reveal its subtle and often hidden dependence on the electrowetting dynamics. We find and experimentally verify that the condition for minimization of droplets’ actuation time is only achieved at the transition. Particularly, the transition time as a function of damping ratio exhibits the general feature of Kramers’ reaction-rate theory.

Delayed Feedback MPC Algorithms of Vehicle Platoons Subject to Constraints on Measurement Range and Driving Behaviors

AbstractThe control problem of vehicle platoons considering sensors with limited measurement range and actuator time delay is investigated in the face of constraints. A new delayed feedback model predictive control scheme is proposed to solve the problem while satisfying the constraints on measurement range and driving behaviors. A family of controllers is presented with free parameters which are then computed by online solving of a receding horizon optimal control problem. Terminal equality constraints are adopted to guarantee stability of the closed‐loop system. Some sufficient conditions with guaranteed string stability of the platoon and zero steady‐state error are established. The effectiveness and advantages of the presented method are demonstrated by simulating two classical road scenarios.

Strain Recovery by TiNi Element Under Fast Heating

A theoretical and experimental study of strain recovery under fast heating of a shape memory alloy (SMA) rod preliminarily stretched in the martensitic state is carried out. Two theoretical models are considered: instantaneous heating and heating with temperature variation during a finite time. In the first case, it is supposed that the straight SMA rod experiences an instantaneous reverse martensitic transformation, and in the second the transformation is supposed to progress at a rate corresponding to the temperature rate. Analytical expression for the time dependence of the rod free-end displacement is obtained. In the experiment, a wire specimen made of titanium-nickel SMA was heated by a short impulse of electric current. The variation of the specimen length in time was registered. Thus, it has been shown that the minimum operation time of an SMA actuator (time needed for the strain recovery) can be reduced to 20 µs. Comparison of the theoretical results with the experimental ones leads to the conclusion that the displacement variation in time is controlled by the rate of heating and the inertia of the specimen. The incubation time of the martensitic transformation on the microscale apparently is estimated as less than 1 µs.

Influence of Humidity and Actuation time on Electromechanical Characteristics of Ionic Polymer-Metal Composite Actuators

This paper experimentally investigates the effects of humidity and actuation time on the electromechanical properties of Ionic Polymer-Metal Composites (IPMC) to improve the practical applications of using the IPMCs as soft biomimetic sensors and actuators. The experiments are conducted in both the open atmosphere (uncontrolled environment at room temperature) and inside a controlled environmental chamber under different input voltages (in term of wave shape, value, and frequency). Results show that the IPMC’s electromechanical properties, namely the deformation capacity and electrical resistance, highly depend on the water content (in the IPMC strip and environment) and the duration of actuation. The Deflection and current of the tested IPMC samples can be represented by an exponential time function were an exponent value decreases with increasing the humidity. IPMC deformation capacity decreases while material electrical resistance increases during activation session. Increasing relative humidity to more than 50% reduces the drying effect on the IPMC deformation capacity and resistance. Also, the IPMC material shows a relaxation behavior for a step voltage input, which can be related to the back immigration of the hydrated cations from the anode to the cathode due to higher pressure at the anode side of the IPMC strip.