Actuator Elements Research Articles

Elastohydrodynamics of a pre-stretched finite elastic sheet lubricated by a thin viscous film with application to microfluidic soft actuators

The interaction of a thin viscous film with an elastic sheet results in coupling of pressure and deformation, which can be utilized as an actuation mechanism for surface deformations in a wide range of applications, including microfluidics, optics and soft robotics. Implementation of such configurations inherently takes place over finite domains and often requires some pre-stretching of the sheet. Under the assumptions of strong pre-stretching and small deformations of the lubricated elastic sheet, we use the linearized Reynolds and Föppl–von Kármán equations to derive closed-form analytical solutions describing the deformation in a finite domain due to external forces, accounting for both bending and tension effects. We provide a closed-form solution for the case of a square-shaped actuation region and present the effect of pre-stretching on the dynamics of the deformation. We further present the dependence of the deformation magnitude and time scale on the spatial wavenumber, as well as the transition between stretching- and bending-dominant regimes. We also demonstrate the effect of spatial discretization of the forcing (representing practical actuation elements) on the achievable resolution of the deformation. Extending the problem to an axisymmetric domain, we investigate the effects arising from nonlinearity of the Reynolds and Föppl–von Kármán equations and present the deformation behaviour as it becomes comparable to the initial film thickness and dependent on the induced tension. These results set the theoretical foundation for implementation of microfluidic soft actuators based on elastohydrodynanmics.

Leveraging Biologically Inspired Models for Cyber–Physical Systems Analysis

Cyber–physical systems (CPS) are systems composed of distributed sensors, physical actuators, and controlling computers that are interconnected through a computer network. Notable examples include: electric utility “smart grids” that can sense and optimize power distribution, transportation systems, and healthcare and medical systems. As CPS complexity increases, system-level trade studies become more challenging due to the combined interaction of the computing, network communications, and physical sensor and actuator elements. Although fundamentally different, complex CPS and biological systems share common attributes that suggest the use of similar modeling approaches. This research investigated if CPS multiobjective optimization methods using mathematical models of a CPS that incorporate biologically inspired CPS system performance objective functions are better than those methods that do not use biologically inspired objective functions. The research methodology employed computer modeling and simulation. A multiobjective optimization study, using a commercially available genetic algorithm-based optimizer, was conducted on four slightly different versions of a dynamic model of a simple distributed robotic sensor system to assess the effect of incorporating a biological mathematical model on the quality of the Pareto fronts generated by the optimizer. An improvement in Pareto front quality was found after incorporating a biological mathematical model.

A poly (vinyl butyral)/graphene oxide composite with NIR light-induced shape memory effect and solid-state plasticity

A NIR light-induced shape memory composite with light-induced plasticity was prepared by incorporating graphene oxide (GO) into cross-linked poly (vinyl butyral) (PVB). The cross-linked reaction between PVB and aromatic diisocyanate not only endowed the composites with excellent shape memory properties, but also offered the performance of solid-state plasticity due to the formation of carbamate bonds. The photo-responsive performance was introduced to the system by doping GO, a conventional photothermal reagent, resulting in excellent NIR light-induced shape memory properties and light-induced plasticity. According to the stress relaxation tests, the solid-state plasticity of composites could be regulated by the cross-linked density, GO, catalyst dosage and temperature. Moreover, the composites can be repeatedly programmed to a new permanent shape via a light-induced plasticity process, which still exhibited excellent light-induced shape memory properties even after 5 cycles of reconfiguration. The results demonstrate the promising prospect of these composites as actuator elements for applications in self-deployment devices and soft robotic.

A MUltidimensional Compliant Decoupled Actuator (MUCDA) for Pelvic Support During Gait

Series Elastic Actuation decouples actuator inertia from the interaction ports and is thus advantageous for force-controlled devices. Parallel or even passive compliance can fulfill a complementary role by compensating for gravitational or periodic inertial forces or by providing passive guidance. Here, these concepts are combined in an underactuated six degree of freedom (6-DoF) compliant manipulator with one actuated DoF. The mechanism comprises a spring assembly in which each spring serves as an actuation element and simultaneously provides passive compliance in the unactuated DoF. The device is designed to assist weight shifting via controlled lateral forces on a human pelvis during treadmill walking and its eigenfrequencies are tuned to align with normal gait. 6-DoF force and torque sensing are realized via a model of the spring deformation characteristics in combination with low-cost inertial and optical sensors. Experimental evaluation demonstrates that the system can effectively follow physiological lateral pelvis movement with low interaction forces and also has little impact on remaining pelvis motions.

Improving hydrodynamic efficiency of composite marine propellers in off-design conditions using shape memory alloy composite actuators

The bend-twist coupling of fibre-reinforced composite laminates has been studied extensively to introduce self-adjustment in pitch angle of marine propellers for improving the hydrodynamic efficiency in off-design conditions. A recent study has shown that for full-scale propellers designed against material failure, the twist generated in the deformed blade due to this effect is not sufficient to cause any noticeable change in the hydrodynamic efficiency. In this paper, we study the use of shape memory alloy (SMA) for inducing variable twist in composite propellers for achieving the same. Prestrained SMA fibres are embedded in the composite in the martensite phase. When SMA fibres are heated upto the austenite phase, a large recovery stress is developed due to the shape memory effect. This stress is used to create twist in the propeller blade through appropriate positioning of the SMA actuators. A full-scale propeller of 4.2 m diameter, made of graphite epoxy with Nitinol fibres as SMA, is considered. The study establishes for the first time that using SMA composite actuator elements, it is possible to generate sufficient twist that can cause the desired improvement in the hydrodynamic performance of full-scale marine propellers at off-design conditions over a wide range of advance ratio.

Design and characterization of the lateral actuator of a bimodal tactile display with two excitation directions

In this paper, a bimodal tactile display used to stimulate the mechanoreceptors is proposed. The use of tactile displays to provide tactile sensations has become the object of increasing interest in recent years. Most of these displays have only one actuator type to generate the tactile perceptions and the spatial resolution of many displays is too rough for good tactile impression. Hence, for the proposed tactile display, two types of actuators for lateral and vertical (normal) excitation are combined. The resolution of the 4 × 4 array is 2.4 mm. Due to its design concept, the presented display is easily expanded. The normal actuator is based on the reluctance principle and the lateral actuator is based on the piezoelectric effect. This contribution focuses on the design and characterization of the piezoelectric actuator. The lateral actuator is mounted on the normal actuator. This has a significant impact on the design of the piezoelectric actuator. To describe the dynamics of this actuator, a Transfer Matrix Method (TMM) Model is created. The mechanical boundary condition at the connection to the normal actuator is included utilizing discrete elements. The model is validated by experiments. Using the model, the geometry of the actuator elements is designed. For performance tests, several experiments have been carried out. The behavior of the lateral actuator has been analyzed in the two end positions of the normal actuators for different load conditions. In terms of performance, the lateral actuators achieve sufficient deflection, even under high load conditions, using imitation human skin as the contact material and with a weight of 50 g. It is shown in a subject test that the lateral actuator works well under real conditions. A measurement of the combined movement has been performed using a Micro System Analyzer (MSA-100-3D) at different frequencies.

Experimental and computational study on phase transformations in superelastic NiTi snake-like spring

One of the major drawbacks of mechanically loaded superelastic NiTi structures is their short fatigue life, which is believed to be related to cyclic variation of relatively large strains due to martensitic phase transformation. Thus, determination of spatial and temporal evolution of martensite within such structures may help to avoid critical loading scenarios in practical applications. However, required data are often difficult to obtain and interpret. In this study, we present a possible approach to this issue and illustrate it on a comprehensive study on isothermal stretching of a planar superelastic NiTi snake-like spring, a prospective versatile superelastic actuator element. Specifically, we complement mechanical, electrical resistivity and x-ray diffraction methods with finite element simulations employing a progressive macroscopic constitutive model and reconstruct the spatial distribution in the most strained parts of the spring. We reveal that martensite tends to form in a localized manner there, which affects distribution of phases as well as strains along the spring. Results also exemplify the substantial influence of tension-compression asymmetry of the superelastic response to distribution of phases within cross-section of a bent structure.

Bioinspired passive variable recruitment of fluidic artificial muscles

This article presents a novel, passive approach to creating variable actuator recruitment in bundles of fluidic artificial muscles. The passive recruitment control approach is inspired by the functionality of mammalian muscle tissues, in which a single activation signal from the nervous system sequentially triggers contraction of progressively larger actuation elements until the required force is generated. Biologically, this behavior is encoded by differences in electrical resistance properties between smaller and larger muscle-fiber groups. The approach presented here produces analogous behavior using a uniform applied pressure to all fluidic artificial muscles while creating differential pressure responses and threshold pressures among the fluidic artificial muscles via tailored bladder elasticity parameters. A model for using elastic bladder stiffness to control an artificial muscle bundle with a single valve is explored and used to compare a bundle of fluidic artificial muscles with both low and high threshold pressure units to a single fluidic artificial muscle of equivalent displacement and force capability. The results of this analysis indicate the efficacy of using this control method; it is advantageous in cases where a wide range of displacements and forces are necessary and can increase efficiency when the system primarily operates in a low-force regime but requires occasional bursts of high-force capability.

Self-Propelled Swimming Microrobot Using Electroosmotic Propulsion and Biofuel Cell

Self-propelled swimming microrobots have significant potential for medical applications. The outstanding technical challenges are the realization of a propulsion mechanism suitable for micro/nanoscale fluids and of an energy supply mechanism that can function inside the human body. Our proposed concept uses electroosmotic propulsion (EOP) and biofuel cell (BFC). The BFC mechanism has a bioanode and a biocathode that generate an open-circuit potential (OCP) by redox reactions of biofuels. The EOP mechanism has an insulating tube arranged between the electrodes. Electroosmotic flow is generated inside the tube by the electric force from the OCP. A reaction force then propels the robot. We derived a theoretical model of the EOP mechanism, which suggested that a smaller robot would have a greater velocity. A microscale prototype was designed and fabricated using an insulating SU-8 layer and two conductive SU-8 layers incorporating enzymes, with glucose and oxygen as the biofuels. “Proof-of-Concept” experiments were conducted using the 100 $\mu$ m prototypes. The observed self-propulsion in the glucose solution was compared with the theoretically estimated values. The results confirmed the validity of the concept. This configuration can be used as a standalone biomedical microrobot, or as an actuator element in a robot system.

MATHEMATICAL MODEL OF A QUICK-DRIVING ACTUATOR OF AN AUTOMATIC SWITCH WITH AN INSTANT-DYNAMIC AND BISTABLE MECHANISM

Purpose. Development of a mathematical model of an induction-dynamic drive of a switch with two coils, working with a bistable mechanism, which ensures the fixation of the instant-dynamic mechanism (IDM) in trajectory extreme positions of the contact system. Methodology . The solution of the problems posed in the work was carried out using methods for calculating the electromagnetic field, finite elements, theoretical mechanics, and solving differential equations. Findings. The mathematical model of quick-driving actuator as part of instant dynamic and bistable mechanism was developed. It was based on electrical circuit’s electromagnetic equations and kinematic movements of the switching mechanism. Advantage of the given model is possibility of a breaker drive dynamic analysis basing on data of a contact pressure, pretravel and snatch gap. Initial data of the model formulation were outer circuit inductance, resistance of coils, which calculated on conductor cross-section and coils configuration. Initial conditions corresponded by Dirichlet conditions. Mathematical model equations system was calculated in cylindrical coordinate system. Problem was solved with the help ComsolMultiphysics system. Motion of the IDM movement part was modeled by deformation of a computational grid. Spring force and stress in a bistable mechanism construction were determined by initial data of a contact pressure, pretravel and snatch gap. Graphs by calculation data are shown, which allow to analyze of springing elements chose and make necessary adjustments on design stage and debugging construction. Operation parameters of mechanism work on IDM switch on and switch off stages were calculated. Value of movement, motion speed of armature breaker, currents of accelerating and retarding coils, summed electromagnetic and opposite force were figured. Originality. The mathematical model of quick-driving actuator as part of instant-dynamic and bistable mechanism was developed. The model contains equations of electromagnetic field and motion equation. The mathematical model describes properly of physical process and can be used for development and research a design of quick-driving actuator. Practical value. It follows from the calculations that with the help of variants of calculations it is possible to obtain the required drive parameters: a) short switching-on time which allows avoiding contact bounce during switching ; b) high initial speed, hole short time (less than 1 ms) of contacts opening and reduce dynamic force on actuator elements and contact system.

Hydrogen-absorbing alloy-based metal-hydride actuation for application in rehabilitative systems.

BACKGROUND: A lightweight rehabilitation assisting system is required to help the aged and disabled with daily life activities, thereby improving the quality of their lives.OBJECTIVE: This paper discusses the development of a metal-hydride (MH) actuator, with excellent heat transfer performance, for application in a rehabilitative system incorporating an MH module.METHODS: The operating mechanism of MH actuators requires that the mechanical power of the pneumatic actuator only be generated via heat transfer through a Peltier element and the absorption/desorption of a hydrogen-contained MH module. To achieve this aim, a 3D model was first designed for two MH modules, and a thermal analysis was carried out according to the type of contact with the Peltier elements to fabricate an MH module with improved heat transfer performance. LabVIEW (National Instruments) was used for automatic temperature control of the Peltier element in the MH actuator driving experiment. ZrTICrFe, which yields a pressure-composition-temperature (PCT) curve of appropriate pressure and temperature ranges for a rehabilitative system, was selected as the hydrogen-absorbing alloy.RESULTS: In addition, the temperature conditions of the MH actuator driving experiment were restricted by two temperature control ranges (30–40C/30–50C) of the Peltier element. Within these Peltier element temperature ranges of 30–40C and 30–50C, results showed that the MH actuator was driven in the ranges of 2–3 atm and 2.5–3.5 atm, respectively.CONCLUSIONS: These findings indicate that the MH actuator proposed in this paper can be utilized to drive a rehabilitative system for elbow and knee joint exoskeletons.

A Thermal-, Water-, and Near-Infrared Light-Induced Shape Memory Composite Based on Polyvinyl Alcohol and Polyaniline Fibers.

A multiresponsive shape memory composite was prepared by incorporating polyaniline (PAn) fibers into polyvinyl alcohol (PVA), where in situ polymerization assisted by surfactant was used to homogeneously disperse PAn fibers in a PVA matrix. The PAn fibers not only increased physical cross-linking points in the system but also served as photothermal conversion reagents, resulting in excellent water-, thermal-, and near-infrared (NIR) light-induced shape memory properties of the composites, where their light-induced shape recovery ratio and speed could be enhanced via the increase of PAn loading percentage and light power density. Moreover, the composites possessed high mechanical properties with tensile strength over 83 MPa. On the basis of these dramatic mechanical properties and shape memory properties, the composites could show high recovery stress over 6.0 MPa, which increased with the increase of temperature and PAn loading percentage. This presented composite could be a great candidate as actuator element for various applications.

Softer is Harder: What Differentiates Soft Robotics from Hard Robotics?

ABSTRACTThis paper reports on what differentiates the field of soft (i.e. soft-bodied) robotics from the conventional hard (i.e. rigid-bodied) robotics. The main difference centres on seamlessly combining the actuation, sensing, motion transmission and conversion mechanism elements, electronics and power source into a continuum body that ideally holds the properties of morphological computation and programmable compliance (i.e. softness). Another difference is about the materials they are made of. While the hard robots are made of rigid materials such as metals and hard plastics with a bulk elastic modulus of as low as 1 GPa, the monolithic soft robots should be fabricated from soft and hard materials or from a strategic combination of them with a maximum elasticity modulus of 1 GPa. Soft smart materials with programmable mechanical, electrical and rheological properties, and conformable to additive manufacturing based on 3D printing are essential to realise soft robots. Selecting the actuation concept and its power source, which is the first and most important step in establishing a robot, determines the size, weight, performance of the soft robot, the type of sensors and their location, control algorithm, power requirement and its associated flexible and stretchable electronics. This paper outlines how crucial the soft materials are in realising the actuation concept, which can be inspired from animal and plant movements.

Автоматизация процесса измерения параметров чувствительных элементов датчи-ков расхода газа

Автоматизация процесса измерения параметров чувствительных элементов датчи-ков расхода газа

Design, optimisation and testing of a compact, inexpensive elastic element for series elastic actuators

This paper presents the development of a compact torsion spring for use as an elastic element in a lightweight series elastic actuator for an active orthosis. This orthosis is going to be utilised as an assistive device for motorically impaired stroke-patients. In the design a two-step optimisation strategy was implemented to meet all requirements for the torsion spring. The first step was to identify a promising topology for the element. In the second step, the shape was optimised based on a finite element model using two different optimisation methods in order to minimise the von Mises equivalent stresses. Four promising variants of the identified topology were extracted from these calculations, one of which was then chosen as the final design. A prototype was manufactured by a laser cutting process, which is a new procedure in the context of elastic elements for series elastic actuators. The calculation results were validated successfully by measurement of the spring properties of this prototype.

Modeling and simulation of high redundancy actuator for fault-tolerance

The High Redundancy Actuator (HRA) deals with the intrinsic fault-tolerance actuation by having a large number of small actuation elements coupled in series and parallel configuration. Each actuation element is a linear Electromechanical Actuator (EMA) and these actuators work collectively to form a single HRA. The mathematical modeling and simulation of a HRA having nine actuation elements in 3×3 series-in-parallel configuration are discussed in the present work. The performance of single actuation element as well as 3×3 HRA are projected under both healthy and faulty conditions. Mathematical modeling equations of single actuation element were solved in MATLAB/Simulink module and based on the results obtained, an iconic model of HRA with series-in-parallel configuration was modeled in Simulink/Simscape module. The simulation results are observed in open-loop and closed-loop control of actuation elements under both healthy and faulty conditions. It was observed that there is no sudden failure of actuation, but there is a graceful degradation in the performance of actuation depending upon the number of faulty elements. However, the actuator was in working condition even after three actuation elements are failed.

Development of a high redundancy actuator with direct driven linear electromechanical actuators for fault-tolerance

The High Redundancy Actuator (HRA) deals with the intrinsic fault-tolerance actuation by having a large number of small actuation elements coupled in series and parallel configuration to form as a single actuator. There is a wide range of actuation elements that are suitable for a HRA, but the present work focused on a direct-driven linear Electromechanical Actuator (EMA). The actuation elements are connected in 3×3 series-in-parallel configuration in the HRA. The mathematical modeling of a single EMA was derived and the equations were solved using MATLAB/Simulink module. Based on the results obtained from the mathematical model, an iconic model of HRA with nine actuation elements was modeled using Simulink/simscape module. The performance of the 3×3 HRA was projected in both open and closed-loop under healthy and faulty conditions. It was observed that there is no sudden failure of actuation, but there is a graceful degradation in the performance of actuation depending upon the number of faulty elements. However, the actuator completes the required task even after the failure of three actuation elements within the HRA.

Geometry and Direct Kinematics to MP3R with 444 Operators

Anthropomorphic mechatronic systems are the most widely used robotics systems worldwide today in industry and in all automated environments. These systems are best suited to the modern automation and mechatronisation needs of the modern world, being mobile, dynamic, light, robust, complex, technologically simple, easy to design and manufactured, implemented, maintained and used in almost any industrial site, both in machine building and in special environments, such as chemical, toxic, dyeing, underwater, nuclear, in space.... Anthropomorphic robots are flexible, dynamic, stable, lightweight, fast, fast, inexpensive, easy-to-install, mechanical, mechanical, mechanical and mechanical systems with a pleasant appearance, modern industrial design and easy to design and implement in any workplace, imposed. In this study we will present the 4×4 operators and the way they can be implemented and used in the complex matrix calculations in order to simplify the complex matrix algebraic numerical methods. 4×4 operators are designed to simplify algebraic matrix calculations by making difficult matrix operations simpler and easier to approach. The method of using 4×4 operators is meant to introduce a degree in addition to the matrices to facilitate algebraic operations. The kinematics of serial manipulators and robots will be exemplified for the 3R kinematic model. The fixed coordinate system was denoted by x0O0y0z0. The mobile systems (rigid) of the three mobile elements (1, 2, 3) have indices 1, 2 and 3. Their orientation has been chosen conveniently. Known kinematic parameters in the direct kinematics are the absolute rotation angles of the three moving elements: φ10, φ20, φ30, angles related to the rotation of the three actuators (electric motors) mounted in the kinematic rotation couplers. The output parameters are the three absolute coordinates xM, yM, zM of point M, i.e., the kinematic parameters (coordinates) of the endeffector (the actuator element (the final), which can be a grasping hand, a solder tip, painted , cut, etc ...). The 3×3 matrix is transformed into 4×4 (it is a mathematical operator) by adding two zero vectors (formed from three elements 0), one line and the other column, and adding one element 1 to the main diagonal (the last element). The matched T01 matrix becomes T014. The column vector matrix (consisting of three elements) undergoes a minimal transformation receiving a fourth fixed value 1 if it is only used for matrix products. The convenient form of matrix A12 is A12c.

Localization of multiple defects using the compact phased array (CPA) method

Array systems of transducers have found numerous applications in detection and localization of defects in structural health monitoring (SHM) of plate-like structures. Different types of array configurations and analysis algorithms have been used to improve the process of localization of defects. For accurate and reliable monitoring of large structures by array systems, a high number of actuator and sensor elements are often required. In this study, a compact phased array system consisting of only three piezoelectric elements is used in conjunction with an updated total focusing method (TFM) for localization of single and multiple defects in an aluminum plate. The accuracy of the localization process was greatly improved by including wave propagation information in TFM. Results indicated that the proposed CPA approach can locate single and multiple defects with high accuracy while decreasing the processing costs and the number of required transducers. This method can be utilized in critical applications such as aerospace structures where the use of a large number of transducers is not desirable.

Lighting Control System for Premises with Display Screen Equipment

The use of Display Screen Equipment (DSE) at enterprises allows one to increase the productivity and safety of production, minimize the number of personnel and leads to the simplification of the work of specialists, but on the other side, changes usual working conditions. If the personnel works with displays, visual fatigue develops more quickly which contributes to the emergence of nervous tension, stress and possible erroneous actions. Low interest of the lighting control system developers towards the rooms with displays is dictated by special requirements for coverage by sanitary and hygienic standards (limiting excess workplace illumination). We decided to create a combined lighting system which works considering daylight illumination and artificial light sources. The brightness adjustment of the LED lamps is carried out according to the DALI protocol, adjustment of the natural illumination by means of smart glasses. The technical requirements for a lighting control system, the structural-functional scheme and the algorithm for controlling the operation of the system have been developed. The elements of control units, sensors and actuators have been selected.