Active Actuators Research Articles

Impact of cryogenic treatment on mechanical and electro active actuation properties of soft polymers

AbstractThe goal of this study is to investigate the change in stretchability property of soft polymers before and after cryogenic treatment. To achieve this, the influences of cryogenic treatment on the rate dependent tensile properties, hysteresis behavior, and stress‐relaxation of soft polymers are extensively analyzed. Results indicated that the effects of cryogenic treatment for both VHB and Ecoflex samples on mechanical responses were more prominent at low strain rate. It was also observed that VHB polymer could exhibit more strain rate sensitivity than Ecoflex sample after cryogenic treatment. For stress relaxation test, both cryo‐treated polymer samples were found to yield less overall stress and takes longer time to reach equilibrium stress in comparison to untreated polymer. Extensive experimental findings showed that the amount of energy dissipated while cooling below glass transition temperature (Tg), causes stress softening with lowering of viscoelastic property. On the other hand, there is a good enhancement of the electro‐active actuation strain for the cryo‐treated VHB 4910 and Ecoflex specimens. The results of this work could be used as a helpful guide for applying cryogenic treatment to improve electro‐mechanical properties of soft polymers, as the theory underlying this treatment has not been well explored

Experimental investigation of turbulent boundary layer dynamics via active manipulation of large-scale structures

The dynamic response of a zero pressure gradient turbulent boundary layer (TBL) to an active flow control actuator was experimentally studied using continous laser particle imaging velocimetry (PIV). In previous experiments using a single hot-wire, it was shown that the synthetic large-scale structure (LSS) introduced by the plasma-based actuator, located in the outer region of TBL, had a strong modulating and reorganizing effect on the near-wall turbulence. In the study reported here, an actuator, optimized for the experimental TBL, was placed at the upper boundary of the log-linear region of the TBL to produce a spanwise uniform, periodic synthetic LSS in order to study the response of the TBL to these large-scale perturbations. Planar PIV over a narrow streamwise region was used to measure the time-resolved, two-dimensional velocity downstream of the actuator at a series of streamwise point locations. Using PIV, the modulating effect of the synthetic LSS on the near-wall turbulence is described in more detail. The results are discussed and compared with previous hot-wire measurements and numerical simulations of the actuated TBL.

Design, fabrication and experiments of a hydraulic active-passive hybrid prosthesis knee.

Due to low friction, passive mechanical prostheses move compliantly followed by the stump and are used widely. Advanced semi-active prostheses can both move passively like passive prostheses and provide active torque under specific conditions. However, the current mechanical-hydraulic coupling driven semi-active prostheses, in order to meet the low passive friction requirements with a low active transmission ratio, lead to a significant problem of insufficient active torque. A hybrid active and passive prosthesis was developed to solve the incompatibility problem of low passive friction and high active driving torque of semi-active prostheses. The mechanical structure and control strategy of the prosthesis were demonstrated. The performance of the prosthesis was tested by bench and human tests. Passive subsystem damping adjustment ranges from 0.4 N⋅(mm/s)-1 to 300 N⋅(mm/s)-1. The switching time between the damping and the active subsystem is 32 ± 2 ms. The continuous active torque output is more than 24 Nm. In level walking, the peak torque is about 28 Nm. The proposed active-passive hybrid hydraulic prosthesis could satisfy both low passive friction and high active actuation.

Optimal Control of an Active Suspension System Applying Distributed Parameter Simulation Test

Automotive is one of the most important industries in the world, which lead to a need for continuous improvement of vehicles and their internal systems. Suspension systems have been improved for better vehicle performance and passenger comfort, keeping the tire in contact with the road surface. Active suspensions require optimal control to modulate the flow of energy and generate the control force by implementing active actuators able to provide negative damping and a wider range of forces and velocities. This article aims the design of an active suspension system based on LQG and LQR controller evaluating its performance in a distributed parameters simulation using COMSOL Multiphysics® and MATLAB®. The quarter car model is proposed and is linearized to design the optimal control (LQG and LQR) respectively. An early mathematical simulation is developed in MATLAB (R) software to verify and compare the open and closed loop results. Finally, the full system model is implemented in COMSOL Multiphysics (R) software considering rigid materials and the controller to analyze the distributed parameters simulation results.

Bioinspired helical-artificial fibrous muscle structured tubular soft actuators.

Biological tubular actuators show diverse deformations, which allow for sophisticated deformations with well-defined degrees of freedom (DOF). Nonetheless, synthetic active tubular soft actuators largely only exhibit few simple deformations with limited and undesignable DOF. Inspired by 3D fibrous architectures of tubular muscular hydrostats, we devised conceptually new helical-artificial fibrous muscle structured tubular soft actuators (HAFMS-TSAs) with locally tunable molecular orientations, materials, mechanics, and actuation via a modular fabrication platform using a programmable filament winding technique. Unprecedentedly, HAFMS-TSAs can be endowed with 11 different morphing modes through programmable regulation of their 3D helical fibrous architectures. We demonstrate a single "living" artificial plant rationally structured by HAFMS-TSAs exhibiting diverse photoresponsive behaviors that enable adaptive omnidirectional reorientation of its hierarchical 3D structures in the response to environmental irradiation, resembling morphing intelligence of living plants in reacting to changing environments. Our methodology would be significantly beneficial for developing sophisticated soft actuators with designable and tunable DOF.

A configuration-optimisation method for passive-active-combined suspension design

Active control can improve the performance of a passive vehicle suspension, but it comes with a high power consumption and large actuator forces. To balance dynamic performance and power/force needs, both the passive and active parts in the suspension should be designed together and work synergistically. Previous approaches that combine passive and active design have been limited to a narrow range of suspension structures, such as passive-active-parallel layouts. This leaves many other structures unable to be explored (e.g., passive-active-series layouts), and thus the current identified design may be far from optimal. Another limitation is that these previous approaches assume an ideal active part and do not consider the parasitic effects of a physical active actuator and its transmission system, such as backlash, friction and inertia. This simplification would hinder their practical application in real-life situations. To address these two limitations, this work introduces a novel design method for passive-active-combined suspensions. Firstly, it allows for the enumeration of all possible suspension designs consisting of a pre-determined number of stiffness, damping, inertance and active actuator elements. Secondly, the method takes into account the parasitic effects that arise from physical realisation when identifying the optimal suspension design. The effectiveness of this method is demonstrated through a quarter-car case study, where the skyhook controller is adopted as an example control strategy. It is found that compared to the traditional combined suspension, the identified design achieves a significant improvement in the trade-off between ride comfort and required active force. The obtained results are verified experimentally.

Influence of Nonlinear Characteristics of Planetary Flywheel Inerter Actuator on Vehicle Active Suspension Performance

The planetary flywheel can significantly reduce the weight of the flywheel, allowing the inerter to be lightweight. When a planetary flywheel ball screw inerter-based active actuator is used in a vehicle suspension system, the nonlinear features of the actuator affect vehicle performance. The planetary flywheel inerter actuator’s nonlinear dynamic model is constructed in this study based on the dynamic features of the planetary flywheel ball screw inerter and the electromagnetic torque generating mechanism of the permanent magnet synchronous motor. The impact of ball screw–nut friction, transmission clearance, planetary gear friction, and gear backlash on the performance of an active tuned inerter damper suspension is then investigated. As a result, the impact and sensitivity of numerous nonlinear parameters on suspension performance are shown, providing a theoretical foundation for the design of planetary flywheel inerter actuator and active inerter suspension.

Pleobot: a modular robotic solution for metachronal swimming

Metachronal propulsion is widespread in aquatic swarming organisms to achieve performance and maneuverability at intermediate Reynolds numbers. Studying only live organisms limits our understanding of the mechanisms driving these abilities. Thus, we present the design, manufacture, and validation of the Pleobot—a unique krill-inspired robotic swimming appendage constituting the first platform to study metachronal propulsion comprehensively. We combine a multi-link 3D printed mechanism with active and passive actuation of the joints to generate natural kinematics. Using force and fluid flow measurements in parallel with biological data, we show the link between the flow around the appendage and thrust. Further, we provide the first account of a leading-edge suction effect contributing to lift during the power stroke. The repeatability and modularity of the Pleobot enable the independent manipulation of particular motions and traits to test hypotheses central to understanding the relationship between form and function. Lastly, we outline future directions for the Pleobot, including adapting morphological features. We foresee a broad appeal to a wide array of scientific disciplines, from fundamental studies in ecology, biology, and engineering, to developing new bio-inspired platforms for studying oceans across the solar system.

Mathematical models and structures of the vehicle lateral stability stabilization system

Currently, intensive research is being carried out to improve the operational characteristics of the car: vibration protection, smoothness, stability, controllability. These properties are largely determined by the characteristics of the vehicle suspension, which provides a connection between the carrier system and the wheels of the vehicle. Significant attention is paid to the development of active suspensions, in which additional actuators are used to form the necessary characteristics, in particular, linear DC motors. The use of active actuators allows you to control the position of the car body, including its lateral roll. In the article, relations are obtained that establish the dependence of additional elastic deformations in the suspension and the car's roll angle on the centrifugal force in a stationary mode. When developing a linearized mathematical model of the control object for the study of non-stationary modes, a two-mass design scheme was used and operator equations were obtained that take into account the elastic-dissipative properties of the sprung and unsprung parts of the car, as well as an additional control action created by the actuator. It is shown that the dynamic properties of the studied control object can be approximately described by the transfer functions of a second-order aperiodic link or an oscillatory link. For the first case, a single-loop system was developed, closed in terms of the angle of heel with a PID controller. In the second situation, it is advisable to use a two-loop system with an internal flexible feedback loop for suspension deformation and an external loop closed for the roll angle using a PID controller. The possibility of forming a feedback signal on the strain rate of the suspension in the wind circuit with the help of an EMF sensor of a linear DC motor is shown.
 On the basis of the block diagram, a computer model of the system was developed, and for typical parameters of the control object, a study was made of transient processes of working off a disturbance in the form of a change in centrifugal force. Based on the simulation results, it was found that the use of the developed ACS provides high accuracy in stabilizing the vehicle roll angle.

Magnetic-Field Mediated Active Propulsion of Ferrofluid Droplets on a Wire.

Droplet actuation on wires or fibers is highly relevant to digital microfluidics applications. Several different passive or active actuation mechanisms have been studied, including capillary pressure, thermal gradient, tilting, acoustics, and electrowetting, to name a few. However, the lack of precise control and accurate droplet positioning during its actuation on a wire limits the use of earlier methods. On the other hand, using a nonuniform magnetic field to actuate a droplet on a micrometer-size wire helps overcome the above limitations. In this context, we elucidate the motion of microliter-size ferrofluid droplets, smaller than the capillary length, in the presence of a permanent magnet using a simple yet robust experimental setup, wherein the clamshell shape droplets hang on a wire at a predetermined distance from the magnet. Beyond a critical volume, the droplet starts moving toward the magnet while exhibiting shape evolution continuously. Using a high-speed videography technique, we uncover the intricate relationship between the magnetowetting, favoring continuous shape evolution of droplets of different sizes, and their actuation dynamics (velocity) on a wire, which has scarcely been explored. The most significant contribution of this study is the detailed evaluation of the shape factor (k), relating the shape evolution of the droplet to its velocity through the contact angle hysteresis force. A theoretical framework has also been proposed, comprising different forces in action, which is found to set forth a good match with the experimental results. The results from this study are expected to open up new avenues in digital microfluidics, specifically in drug delivery, ferrobotics, and droplet logic gates, to name a few.

Twin Bearingless Machine Drive Configurations With a Reduced Number of Inverters

Bearingless motors combine torque and magnetic levitation into a single electric machine. Recent research indicates that this technology has the potential to yield a reliable, oil-free, highly-efficient, and integrated solution for industrial applications if the cost associated with the electric drive can be reduced. This paper investigates power electronic implementations that reduce the required number of inverters, and thereby reduce the drive cost. The paper targets electric machinery for significant power applications, such as compressor systems, which require active actuation in all degrees of freedom (DOF). The paper shows that by implementing the system as a twin bearingless machine configuration, with each machine using a combined winding, the number of inverters (and supporting components) can be reduced by 25% through novel connections of the winding coil groups. Nine reduced-component twin bearingless machine drive configurations are proposed, evaluated, and compared. Power electronic and control implementations are proposed and experimental results demonstrate reduced-component drives levitating a prototype twin machine and controlling machine coil currents identically to the conventional (full-cost) bearingless drive.

Concept design of hybrid-actuated lower limb exoskeleton to reduce the metabolic cost of walking with heavy loads.

This paper proposes the conceptual design method for a hybrid-actuated lower limb exoskeleton based on energy consumption simulation. Firstly, the human-machine coupling model is established in OpenSim based on the proposed three passive assistance schemes. On this basis, the method of simulating muscle driving is used to find out the scheme that can reduce the metabolic rate the most with 3 passive springs models. Then, an active-passive cooperative control strategy is designed based on the finite state machine to coordinate the operation of the power mechanism and the passive energy storage structure and improve the mobility of the wearer. In the end, a simulation experiment based on the human-machine coupled model with the addition of active actuation is proceeded to evaluate its assistance performance according to reducing metabolic rate. The results show that the average metabolic cost decreased by 7.2% with both spring and motor. The combination of passive energy storage structures with active actuators to help the wearer overcome the additional consumption of energy storage can further reduce the body's metabolic rate. The proposed conceptual design method can also be utilized to implement the rapid design of a hybrid-actuated lower limb exoskeleton.

Precise Configuring of Actuators/Sensors for Active Control of Sound Quality in Cabs with Modal Vibration Energy and LA-PSO

Active control of structural modal vibration is an effective strategy to enhance the sound quality of cabs in commercial vehicles. However, accurate determination of the positioning and quantity of modal active control sensors and actuators is crucial for cabs with intricate structures, owing to the presence of multiorder modes and their coupling. The study presented herein focuses on the cab of a commercial vehicle and contemplates the features of the irregular large-space structure of the cab. By capitalizing on the modal frequency and mode shape of the cab, utilizing the piezoelectric control principle and modal vibration energy as the assessment index, an advanced multimode composite control criterion is postulated to ascertain the configuration of primary sensors and actuators. The particle swarm optimization (PSO) objective function is constructed to accomplish the optimal position matching of the actuator/sensor, using the multimodal surface velocity vector of the vibration sensor as the core parameter. Furthermore, an improved linear adaptive particle swarm optimization (LA-PSO) technique is advanced to satisfy the requirements of optimal convergence performance and accuracy of the complex cab structure. The optimization culminates in a 9 × 9 multichannel active control scheme for determining the optimal position of the actuators/sensors. This investigation provides a technical foundation for the active control of sound quality in automotive cabs and presents an innovative method for implementing effective noise control systems in large-scale machinery and equipment.

A Review of Rehabilitative and Assistive Technologies for Upper-Body Exoskeletal Devices

This journal review article focuses on the use of assistive and rehabilitative exoskeletons as a new opportunity for individuals with diminished mobility. The article aims to identify gaps and inconsistencies in state-of-the-art assistive and rehabilitative devices, with the overall goal of promoting innovation and improvement in this field. The literature review explores the mechanisms, actuators, and sensing procedures employed in each application, specifically focusing on passive shoulder supports and active soft robotic actuator gloves. Passive shoulder supports are an excellent option for bearing heavy loads, as they enable the load to be evenly distributed across the shoulder joint. This, in turn, reduces stress and strain around the surrounding muscles. On the other hand, the active soft robotic actuator glove is well suited for providing support and assistance by mimicking the characteristics of human muscle. This review reveals that these devices improve the overall standard of living for those who experience various impairments but also encounter limitations requiring redress. Overall, this article serves as a valuable resource for individuals working in the field of assistive and rehabilitative exoskeletons, providing insight into the state of the art and potential areas for improvement.

An Active Compliance Adsorption Method for Climbing Machining Robot on Variable Curvature Surface

This article proposes an active compliance adsorption method for a negative pressure adsorption climbing robot with 3 active compliance suction units which integrate 3 degree of freedom active compliance actuators along with flexible adsorption chambers. This method enables the climbing robot to adsorb and move stably on the surface of large and complex components with variable curvature for machining purposes. The main contribution lies in two aspects. First, an adsorption performance indicator (API) depicting the stretch of the flexible sealing lip is proposed by analyzing the leaked airflow of the climbing robot's suction unit. Second, the pose control method of the suction chamber based on the real-time estimated adsorbed surface is proposed, where the API is used as the optimization target. The experiments have been performed and the results show that a 10 kg-weight climbing robot with three active compliance suction units can keep adsorption force over 1000 N when the surface's curvature radius changes continuously from 1.1 to 14.6 m, with a significant increase in the adsorption force up to 156% compared with only pure passive compliance adsorption method.

Numerical simulation of hypersonic plasma flow field disturbed by pulsed discharge

A plasma sheath will be generated around the hypersonic vehicle during reentry, and a large number of electrons in the plasma sheath will seriously affect the communication between the vehicle and the ground station. In order to reduce the electron number density of the hypersonic vehicle plasma sheath, a method of using pulsed discharge active actuation to regulate the plasma sheath is proposed. Based on the air dissociation and ionization model including 11 components and 32 chemical reactions, the reduction effect of pulsed discharge actuation on the electron density of plasma sheath is studied by numerical simulation. A first test is performed in which the pulsed discharge is compared with the plasma jets' experimental data. Then, a second test compared the plasma flow field around the RAMC-II vehicle with the flight test and NASA data. In these two tests, the simulation results are basically consistent with the experimental results. Finally, the effect of pulsed discharge with different energy density on the plasma sheath electron density is studied. The numerical results show that the interaction between the high-pressure aerodynamic actuation generated by the actuator and the plasma sheath produces an obvious shock wave, which blocks electrons from flowing downstream, reduces the velocity and pressure of the flow field behind the shock wave, and, finally, makes the electron density downstream of the actuator attenuate significantly, with the maximum attenuation amplitude of about 35%. Compared with the traditional method, the method proposed in this paper requires less space, load, and source power and has certain engineering feasibility.

Analysis of a Soft Bio-Inspired Active Actuation Model for the Design of Artificial Vocal Folds

AbstractPhonation results from the passively induced oscillation of the vocal folds in the larynx, creating sound waves that are then articulated by the mouth and nose. Patients undergoing laryngectomy have their vocal folds removed and thus must rely on alternative sources of achieving the desired vibration of artificial vocal folds. Existing solutions, such as voice prostheses and the Electrolarynx, are limited by producing sufficient voice quality, for instance. In this paper, we present a mathematical analysis of a physical model of an active vocal fold prosthesis. The inverse dynamical equation of the system will help to understand whether specific types of soft actuators can produce the required force to generate natural phonations. Hence, this is referred to as the active actuation model. We present the analysis to replicate the vowels /a/, /e/, /i/, and /u/ and voice qualities of vocal fry, modal, falsetto, breathy, pressed, and whispery. These characteristics would be required as a first step to design an artificial vocal folds system. Inverse dynamics is used to identify the required forces to change the glottis area and frequencies to achieve sufficient oscillation of artificial vocal folds. Two types of ionic polymer-metal composite (IPMC) actuators are used to assess their ability to produce these forces and the corresponding activation voltages required. The results of our proposed analysis will enable research into the effects of natural phonation and, further, provide the foundational work for the creation of advanced larynx prostheses.

Free and Forced Vibration Behaviors of Magnetodielectric Effect in Magnetorheological Elastomers

This paper is concerned with the free and forced vibration responses of a magneto/electroactive dielectric elastomer, emphasizing the chaotic phenomena. The dielectric elastomers under external magnetic and electrical excitations undergo large elastic deformation. The magnetodielectric elastomer is modeled based on the Gent–Gent strain energy function to incorporate the influence of the second invariant and the strain stiffening. The viscoelasticity of the active polymer is also considered in the form of Rayleigh’s dissipation function. The equation of motion is governed with the aid of the Lagrangian equation in terms of a physical quantity, namely, the stretch of the elastomer. An energy-based approach is utilized to re-evaluate the static and DC voltage instabilities of the resonator. Time-stretch response (time history behavior), phase plane diagram, Poincaré map, and fast Fourier transform are numerically obtained and presented to explore the chaotic oscillation behavior of the active polymer actuators. The results reveal that the magnetic field may tune the stability and instability regions of the active polymeric membrane. It has also been shown that the applied magnetic field may lead to chaotic vibration responses when a sinusoidal voltage is applied simultaneously to the system. The results presented in this paper can be effectively used to design magnetic and electrical soft robotic actuators and elastomer membranes under electrical and magnetic stimulants.

Enhancing the trade-off between ride comfort and active actuation requirements via an inerter-based passive-active-combined automotive suspension

Ride comfort is an important indicator to evaluate the dynamic performance of automotive vehicles. One method for improving ride comfort is to incorporate an active actuator into the passive suspension. However, the improvement is closely linked with the required actuation power and force. Increased actuation requirements may lead to higher energy consumption and a larger actuator size. To enhance the trade-off between ride comfort and active actuation requirements, a new design approach for searching for the optimal passive-active-combined suspension across many different mechanical component layouts incorporating an inerter is proposed in this paper. Compared with traditional designs where the suspension is limited to a few special layouts, via this approach the optimal passive part among all network possibilities with pre-determined numbers of each element type (springs, dampers and inerters), and optimal controller parameters of the parallel active actuator can be identified. Considering a quarter-car model, with a benchmark combined active-passive suspension in which the passive part is a spring-damper, the optimal inerter-based suspension can reduce the active force by more than 48% and regenerate 6 W more average power in the active part while achieving the same ride comfort. Note that in this case, two constraints are always considered: the road-holding ability (as indicated by the dynamic tyre load) and suspension travel of the identified suspension will not be worse than those of the benchmark suspension. The optimal trade-off obtained with this approach serves as a powerful tool in the automotive suspension design as it provides guidance on the following three aspects: the optimal ride comfort, the minimum power consumption and the feasibility of specific actuation requirements, where the second point is obtained in conjunction with the power conservation theorem proposed in this paper which proves that the total power consumed by the passive and active parts will not vary with changes in the passive part and active controller parameters.

Observer-Based Optimal Control of a Quadplane with Active Wind Disturbance and Actuator Fault Rejection.

Hybrid aircraft configurations with combined cruise and vertical flight capabilities are increasingly being considered for unmanned aircraft and urban air mobility missions. To ensure the safety and autonomy of such missions, control challenges including fault tolerance and windy conditions must be addressed. This paper presents an observer-based optimal control approach for the active combined fault and wind disturbance rejection, with application to a quadplane unmanned aerial vehicle. The quadplane model is linearised for the longitudinal plane, vertical takeoff and landing and transition modes. Wind gusts are modelled using a Dryden turbulence model. An unknown input observer is first developed for the estimation of wind disturbance by defining an auxiliary variable that emulates body referenced accelerations. The approach is then extended to simultaneous rejection of intermittent elevator faults and wind disturbance velocities. Estimation error is mathematically proven to converge to zero, assuming a piecewise constant disturbance. A numerical simulation analysis demonstrates that for a typical quadplane flight profile at 100 m altitude, the observer-based wind gust and fault correction significantly enhances trajectory tracking accuracy compared to a linear quadratic regulator and to a H-infinity controller, which are both taken, without loss of generality, as benchmark controllers to be enhanced. This is done by adding wind and fault compensation terms to the controller with admissible control effort. The proposed observer is also shown to enhance accuracy and observer-based rejection of disturbances and faults compared to three alternative observers, based on output error integration, acceleration feedback and a sliding mode observer, respectively. The proposed approach is particularly efficient for the active rejection of actuator faults under windy conditions.