Deformation Of Actuators Research Articles

Development of gait assistive clothing-typed soft wearable robot for elderly adults

PurposeThe purpose of this research was to develop clothing-typed soft wearable robot embedded with textile-based actuators on ankles for elderly adults needing gait assistance.Design/methodology/approachDesign guidelines were developed and they included function (type, targeting area, routing line and anchor points), design (size/fit, fabric/material, fastener, detail, color) and actuator (shape memory alloy type, size, deformation type, integration material, integration technique and evaluation method). Fabric-based actuator, integration methods to fabrics, routing lines and anchoring points were developed based on the guidelines and evaluated. Then, three long socks types and a pants type were designed and prototyped. Routing line position displacement measurement test was conducted with the prototypes. A survey was conducted to investigate satisfaction, likeness and use intention on the design/prototype to modify the designs.FindingsImportant design factors were identified, and design guidelines for clothing-typed soft wearable robots (SWRs) were developed. People satisfied the developed SWR designs and prototypes with mean scores over 4.60.Originality/valueThe results are expected to be helpful for designers and developers of SWRs in the development process, and they will ultimately be beneficial to members of the elderly population who have gait difficulties.

A New Soft RCC Device with Pneumatic Regulation

The work described in this paper aims at exploiting the characteristic of a special deformable actuator with rolling membranes to realize a device with defined Remote Center of Compliance (RCC). Starting from theoretical approaches to the definition of the RCC, the authors propose a novel and simple formulation that can be applied to the soft actuator to determine its RCC. The position of the device’s RCC was determined by creating an asymmetry on the geometry of the device along its axis, i.e., by imposing a longitudinal displacement to the piston with respect to the membranes’ rest condition. FEM simulations of the device behavior were carried out and a first formulation describing the placement of the RCC by varying the operating pressure was found. Finally, a comparison of the theoretical model and FEM results is presented, validating the proposed formulation.

Quantifying the equilibrium swelling responses and swelling-induced snap-through of heterogeneous spherical hydrogels

We employ the finite deformation theory to analyze the inhomogeneous large deformation of a heterogeneous spherical hydrogel subjected to chemo-mechanical loadings. The heterogeneous spherical hydrogel is composed of two concentric spherical hydrogel layers with different material properties. The Gent model is employed for the free energy function of the polymer stretching part in order to tackle the effect of the limiting chain extensibility. The heterogeneous spherical hydrogel is assumed to be perfectly bonded at the interface and is traction free at the external surface. At the internal surface, two boundary conditions are considered: one is internally fixed and the other is internally pressurized. Numerical examples are performed to describe the nonlinear behaviors of a heterogeneous spherical hydrogel when subjected to the swelling and mechanical loadings. For internally fixed case, numerical results show that the limiting chain extensibility and the initial swelling ratio have significant effect on the actuation deformation of a heterogeneous spherical hydrogel. For internally pressurized case, we find that the swelling-induced snap-through instability can be triggered under specified conditions. It is shown that the chemo-mechanical behaviors of the heterogeneous spherical hydrogels can be adjusted by tuning the material properties and the initial swelling ratios.

Self-Sensing and Control of Soft Electrothermal Actuator

Soft electrothermal actuators have been of particular interest to researchers in soft mechatronic/robotic systems due to their large deformation, lightweight, and low power actuation. Closed-loop control of soft actuators is critical for high-precision applications, due to the nonlinear relationship between actuation voltage and output bending motion. In this article, a resistive self-sensing approach was developed for the soft electrothermal actuator, which enables the closed-loop control of the actuator without external sensors. The self-sensing of the actuator's deformation is achieved by measuring the resistance change of the embedded microfilament heater of the soft electrothermal actuator. When the bimorph electrothermal actuator deflects under the temperature change, its deflection can be detected by the temperature-incurred resistance change of the embedded heater. A closed-loop controller was designed using the self-sensed deflection signal. To handle the different responses of the actuator in the heating and cooling stages, a switching proportional-integral-derivative control algorithm was designed. Specifically, two sets of control parameters were tuned and used for the heating and cooling stages, respectively. The performance of the designed control algorithm was evaluated for step response, tracking of complex wave signals, and disturbance rejection. Compared with the open-loop operation, the closed-loop controlled actuator demonstrated a much more rapid and accurate response (the rising time and settling time were reduced over 80%) and excellent tracking and disturbance rejection capabilities.

A Fabrication Free, 3D Printed, Multi-Material, Self-Sensing Soft Actuator

Soft robotics offers a range of attractive features relative to traditional rigid robots, including inherently safer human-robot interactions, and continuous passive dynamics that enable morphological computation. Here we present an actuator with an integrated print-in-place strain sensor which is produced entirely via multi-material additive manufacturing and requires no post processing or manual fabrication steps. One natural application of this technology is the end effector of robotic arms; incorporating deformable actuators into a gripping mechanism allows for the safe integration of robotic assistance in human-occupied settings. While numerous soft robot actuators have been implemented without feedback, force sensing and proprioception are valuable signals to leverage in extending the capabilities of these systems. Prior approaches to integrating sensors into soft robot components have relied on manual processes, or specialized fabrication tools. Our work shows a novel method for automatically manufacturing soft pneumatically-driven actuators with embedded sensors through readily available 3D printing tools with no human fabrication required. Automatically manufacturing these sensor-actuator systems enables more complex, capable, and integrate-able designs, because the labor of assembly is eliminated; actuator-sensor designs that would be tedious or impossible to manufacture become tractable with our approach.

Soft actuator with large volumetric change using vapor–liquid phase transition

Soft robotics has become an attractive research topic with the recent development of soft actuators. Herein, we propose a deformable soft actuator with large volumetric changes. The proposed elastomer contains liquid droplets; their transition from the liquid phase to the vapor phase can be controlled by heat. We chose silicone and urethane rubbers as the matrix materials; droplets of water and fluorine were dispersed homogeneously in the rubber matrix as micelles or solutes. After curing the rubber, bubbles appeared owing to microwave heating. We succeeded in generating a fine bubble structure using the proposed method, and we could reduce the leakage of the droplet material using urethane as the matrix material. Finally, we attempted to fabricate a small actuator to work in the channels. The proposed method can be useful for miniaturized soft robots.

Somatosensory, Light-Driven, Thin-Film Robots Capable of Integrated Perception and Motility.

Living organisms are capable of sensing and responding to their environment through reflex-driven pathways. The grand challenge for mimicking such natural intelligence in miniature robots lies in achieving highly integrated body functionality, actuation, and sensing mechanisms. Here, somatosensory light-driven robots (SLiRs) based on a smart thin-film composite tightly integrating actuation and multisensing are presented. The SLiR subsumes pyro/piezoelectric responses and piezoresistive strain sensation under a photoactuator transducer, enabling simultaneous yet non-interfering perception of its body temperature and actuation deformation states. The compact thin film, when combined with kirigami, facilitates rapid customization of low-profile structures for morphable, mobile, and multiple robotic functionality. For example, an SLiR walker can move forward on different surfaces, while providing feedback on its detailed locomotive gaits and subtle terrain textures, and an SLiR anthropomorphic hand shows bodily senses arising from concerted mechanoreception, thermoreception, proprioception, and photoreception. Untethered operation with an SLiR centipede is also demonstrated, which can execute distinct, localized body functions from directional motility, multisensing, to wireless human and environment interactions. This SLiR, which is capable of integrated perception and motility, offers new opportunities for developing diverse intelligent behaviors in soft robots.

Experimental study of axial-compressed macro-fiber composite bimorph with multi-layer parallel actuators for large deformation actuation

Piezoelectric bimorphs have a promising application in morphing micro air vehicles; however, increasing the actuation displacement is a difficult point. Axial compression can be used to increase the deformation of the piezoelectric bimorph. Compared with piezoelectric ceramics, macro fiber composites offer higher flexibility. In this article, a large displacement actuator of axial-compressed macro fiber composite bimorph is proposed. A multi-layer parallel scheme of macro fiber composite bimorphs is presented to increase the output torque of piezoelectric bimorph within a limited space. The actuation performance of the axial-compressed macro fiber composite bimorph and its multi-layer parallel scheme are verified through quasi-static experiment and displacement tracking control test. The experimental results show that the end-free rotations of both the axial-compressed macro fiber composite bimorph and its multi-layer scheme achieve ±8.1°, which is 60% higher than that of a piezoelectric ceramics bimorph with the same length. The blocking torque of the single-layer macro fiber composite bimorph is 0.028 Nm. The proposed parallel bimorphs method can magnify output torques. In addition, the axial-compressed macro fiber composite bimorph can accurately track any displacement signals in the range of its actuation. It is a continuous and controllable piezoelectric bimorph with large displacement.

Programmable deformation of patterned bimorph actuator swarm.

Graphene-based actuators featuring fast and reversible deformation under various external stimuli are promising for soft robotics. However, these bimorph actuators are incapable of complex and programmable 3D deformation, which limits their practical application. Here, inspired from the collective coupling and coordination of living cells, we fabricated a moisture-responsive graphene actuator swarm that has programmable shape-changing capability by programming the SU-8 patterns underneath. To get better control over the deformation, we fabricated SU-8 micropattern arrays with specific geometries and orientations on a continuous graphene oxide film, forming a swarm of bimorph actuators. In this way, predictable and complex deformations, including bending, twisting, coiling, asymmetric bending, 3D folding, and combinations of these, have been achieved due to the collective coupling and coordination of the actuator swarm. This work proposes a new way to program the deformation of bilayer actuators, expanding the capabilities of existing bimorph actuators for applications in various smart devices.

Условие абсолютной устойчивости системы управления электроупругим актюатором для наномехатроники

An electroelastic actuator for nanomechatronics is used in nanotechnology, adaptive optics, microsurgery, microelectronics, and biomedicine to actuate or control mechanisms, systems based on the electroelastic effect, and to convert electrical signals into mechanical displacements and forces. In nanomechatronic systems, a piezoactuator is used in scanning microscopy, laser systems, in astronomy for precision alignment, for compensation of temperature, gravitational deformations and atmospheric turbulence, focusing, and stabilizing the image. In this study, a condition for absolute stability of an electroelastic actuator control system for nanomechatronics under deterministic and random inputs is obtained. A number of equilibrium positions in an electroelastic actuator mechatronic control system are found, the totality of which is represented by a straight line segment. The electroelastic actuator’s deformation control system dead band relative width is determined for the actuator’s symmetric and asymmetric hysteresis characteristics. Under deterministic inputs and with fulfilling the condition for the derivative of the nonlinear hysteresis actuator deformation characteristic, the set of equilibrium positions of the electroelastic actuator control system for nanomechatronics is absolutely stable. Under random inputs, the system absolute stability with respect to the mathematical expectations of the electroelastic actuator mechatronic control system equilibrium positions has been determined subject to fulfilling the condition on the derivative of the actuator hysteresis characteristic.

Experimental and numerical analyses of a rotary motor using shape memory alloy mini springs

The rotation mechanism based on an eccentric, combined with large deformations of SMA spring type actuators, allowed the design of a compact device with continuous rotation. The proposed rotary motor is driven by NiTi shape memory alloy (SMA) springs. The springs are driven by an electric current using the Joule effect as a physical principle. In this case, the motor can rotate in both directions, by only inverting the drive sequence. When driven, SMA springs combine the superelastic effect (SE) and the shape memory effect (SME), and can suffer deformations of up to 600% of their initial length. To define the design parameters, an electro-thermomechanical characterization of the SMA springs was performed, in addition to antagonistic tests to evaluate the generation of work after thermal heating. An experimental set-up measured the angular displacement, force and torque responses generated by the motor. For the numerical simulations, three different models were tested in order to define which of them best represents the behavior of force and deflection of the actuators. The most appropriate model was selected for the analyses of the static responses of the motor in rotation. The operation of the prototype was demonstrated for different driving modes, presenting results of movement, force, torque and temperature of the actuators. Numerical simulations presented a maximum error of 5.13% when compared to the experiment. The contribution of this work are numerical simulations of a rotating motor, correlated with experimental measurements. It is demonstrated that the proposed motor is in a prominent position regarding its torque/volume and torque/mass ratios when compared to other motors of the same class.

Dielectric elastomer film with anisotropic actuation deformation on film plane

ABSTRACTA new dielectric elastomer (DE) film, which was able to show anisotropic large plane deformation actuated by an external electric field, was designed and synthesized. Specifically, an asymmetric di‐vinyl monomer cyclohex‐3‐enylmethyl acrylate (CEA) was incorporated into the middle block of poly(styrene‐b‐butyl acrylate‐b‐styrene) as potential crosslinking points. By widely used UV curing technique through a mask, the DE films could be locally hardened any area one selected. This could break the symmetry of the actuation deformation on the DE film plane, maximizing the deformation in a given direction while the actuation area strain remained unchanged. The actuation strainy/strainx reached 2.3, strain in x direction was 10.3% while in y direction was 23%, when the DE film of S(BA‐ran‐CEA)S with 2.5 mol % CEA incorporated was locally hardened in the form of soft and hard belt of 1 mm width alternatively along y direction. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48795.

Kirigami-Based Light-Induced Shape-Morphing and Locomotion.

The development of stimuli-responsive soft actuators, a task largely undertaken by material scientists, has become a major driving force in pushing the frontiers of microrobotics. Devices made of soft active materials are oftentimes small in size, remotely and wirelessly powered/controlled, and capable of adapting themselves to unexpected hurdles. However, nowadays most soft microscale robots are rather simple in terms of design and architecture, and it remains a challenge to create complex 3D soft robots with stimuli-responsive properties. Here, it is suggested that kirigami-based techniques can be useful for fabricating complex 3D robotic structures that can be activated with light. External stress fields introduce out-of-plane deformation of kirigami film actuators made of liquid crystal networks. Such 2D-to-3D structural transformations can give rise to mechanical actuation upon light illumination, thus allowing the realization of kirigami-based light-fuelled robotics. A kirigami rolling robot is demonstrated, where a light beam controls the multigait motion and steers the moving direction in 2D. The device is able to navigate along different routes and moves up a ramp with a slope of 6°. The results demonstrate a facile technique to realize complex and flexible 3D structures with light-activated robotic functions.

PEDOT coating enhanced electromechanical performances and prolonged stable working time of IPMC actuator

Current ionic exchange polymer metal composite (IPMC) has always been associated with short stable working time due to the presence of severely electrode fatigue and water loss, which limits its wide-spread applications. To address this problem, a facile and effective strategy has been proposed to repair the IPMC by electrografting a conductive, flexible polymer of Poly(ethylenedioxythiophene) (PEDOT) on IPMC electrode surface in this study. The investigation of physiochemical properties of PEDOT coating revealed that EDOT molecules could fill into the electrode cracks generated from fatigue and then were polymerized into PEDOT with a linear conjugation structure. The PEDOT-coated electrodes exhibited significantly improved conductivity and effectively reduced water loss. The PEDOT coating can repair the common actuation defects of the used IPMC actuators, such as asymmetrical actuation and torsional deformations. Moreover, the introduction of PEDOT coating apparently improved electromechanical properties by increasing swing angles and displacements, and prolonging the stable working time to more than 1000sec without fatigue.

An Optimum Design Method of Pneu-Net Actuators for Trajectory Matching Utilizing a Bending Model and GA

This study addresses the problem in designing pneu-net actuators to achieve specific target trajectories for particular applications. The finite element analysis (FEA) method is used to study the sensitivity of 9 design parameters to bending deformation of actuators, and the results of FEA demonstrate that the width of the chamber and the width of the middle layer have great influence on the bending performance. Besides, the relations between the bending angles of actuators with different width parameters and the pressure are always highly linear. Using FEA and the cubic polynomial fitting algorithm, a unified bending model of the pneu-net actuator is established with three crucial design parameters (i.e., segment length, chamber width, and middle-layer width). An optimum design method based on the bending model and genetic algorithm (GA) is put forward to automatically adjust these three crucial parameters to realise trajectory matching. The method is developed to be an effective solution for the problem in matching the target trajectory with the experimental results achieved on an actuator designed by imitating a human index finger. Furthermore, the results of the experiment also verify that the actuator can achieve stable grasping, and the proposed method has an important directive to design pneu-net actuators for their application in the fields of robotics, rescue, and detection.

Effective enhanced model for a large deformable soft pneumatic actuator

Soft pneumatic actuators have been widely used for implementing sophisticated and dexterous movements, due to numerous fascinating features compared with their rigid counterparts. Relatively speaking, modeling and analysis of an entire soft pneumatic actuator considering contact interaction between two adjacent air chambers is extremely rare, which is exactly what we are particularly interested in. Therefore, in order to establish an accurate mechanical model and analyze the overall configuration and stress distribution for the soft pneumatic actuator with large deflection, we consider the contact interaction of soft materials rather than hard materials, to produce an effective enhanced model for soft contact of a large deformable pneumatic actuator. In this article, a multiple-point contact approach is developed to circumvent the mutual penetration problem between adjacent air chambers of the soft actuator that occurs with the single-point contact approach employed in linear elastic rigid materials. In contrast to the previous simplified rod-based model that did not focus on contact interaction which was adopted to clarify the entire deformation of the actuator, the present model not only elaborates nonlinear large deformation and overall configuration variations, but also accurately delineates stress distribution law inside the chamber structure and the stress concentration phenomenon. By means of a corresponding static experiment, a comparison of the simulation results with experimental data validates the effectiveness and accuracy of this model employing a multiple-point contact approach. Excellent simulation of the actual bending deformation of the soft actuator is obtained, while mutual penetration is successfully circumvented, whereas the model with single-point contact cannot achieve those goals. Finally, as compared with the rod-based model, the results obtained using the proposed model are more consistent with experimental data, and simulation precision is improved.

Investigation into post constrained recovery properties of nickel titanium shape memory alloys

Experimental investigations have found that nickel titanium (NiTi) shape memory alloys (SMAs) exhibit a phenomenon wherein the material can be recoverably deformed in its low temperature martensitic state, thermally actuated to its austenite state while constrained from returning to its parent geometry, and upon ceasing actuation and return to the low temperature martensite state it will continue to generate post constrained recovery residual stresses (PCRRS). The ability to generate a PCRRS creates a new way for SMAs to be used but the stability of the PCRRS, response to subsequent loading, and underlying microstructural mechanisms that generate the PCRRS are poorly understood. This paper presents an experimental investigation into the thermomechanical response of NiTi beginning from a PCRRS state. Multiple formulations of NiTi were exposed to training and sequences of cyclic deformation and thermal actuation in this study. It was found that repeated application of 0.5% strain reduced the residual stress with each application and thermal actuation would restore the original PCRRS. Training and mechanically working the material stabilized the thermomechanical response and did not significantly degrade the magnitude of the PCRRS. Understanding of PCRRS supports a new way for materials to be used as actuators, storing potential energy in material structures that may be beneficial to self-healing material, fatigue crack prevention and other applications.

Peristaltic locomotion without digital controllers: Exploiting multi-stability in origami to coordinate robotic motion

This study examines a novel approach to generate peristaltic-like locomotion in a segmented origami robot. Specifically, we demonstrate the use of multi-stability embedded in the origami skeleton to eliminate the need for multiple actuators or digital controllers to coordinate the complex robotic movements in peristaltic crawling. The crawling robot in this study consists of two serially connected bistable origami segments, each featuring a generalized Kresling design and a foldable anchoring mechanism. Mechanics analysis and experimental testing reveal that the nonlinear elastic behaviors of this dual-segment module, especially its rapid deformation due to the non-monotonic energy landscape and force–displacement relationship, can create a deterministic deformation sequence or actuation cycle. This cycle can then be used to generate the different phases in a peristaltic-like locomotion gait. Instead of individually controlling the segment deformation like in earthworm and other crawling robots, we only control the total length of this robot. Therefore, this approach can significantly reduce the total number of actuators needed for locomotion and simplify the control requirements. Moreover, the richness in Kresling origami design offers us substantial freedom to tailor the locomotion performance. The results of this study will contribute to a paradigm shift in how we can use the mechanics of multi-stability for robotic actuation and control.

Photoresponsive Graphene Composite Bilayer Actuator for Soft Robots.

Highly deformable and photoresponsive smart actuators are attracting increasing attention. Here, a high concentration of graphene is dispersed in polydimethylsiloxane (PDMS) by combining the advantages of various dispersion methods. The composite and pure PDMS layers are used to fabricate bilayer actuators with a high capacity for rapid deformation. The fabricated bilayer actuators exhibit novel and interesting properties. A bilayer actuator containing a 30 wt % graphene composite can be deflected by 7.9 mm in the horizontal direction under infrared laser irradiation. The graphene concentration in the composite influences actuator adjustment to deformation and its response speed, and the composite also exhibits superhydrophobicity. On the basis of its superhydrophobicity and large deformation capacity, the actuator made with 30 wt % graphene composite is used to construct a beluga whale soft robot. The robot can swim quickly in water at an average speed of 6 mm/s, and it can cover a distance of 30 mm in 5 s when irradiated just once with an infrared laser. Actuators fabricated with this method can be used in artificial muscle, bionic grippers, and various soft robots that require actuators with large deformation capacities.

Voltage-controlled morphing of dielectric elastomer circular sheets into conical surfaces

Dielectric elastomers provide large, fast, and reversible deformations which can be harnessed to provide predefined sophisticated actuation deformations. This paper describes a method, fabrication technique and analysis tools for morphing flat sheets of dielectric elastomers into conical shapes upon applying a voltage, using a set of concentric, stiff rings that are 3D-printed onto a multilayer elastomer sheet. A finite elements user-subroutine and a simple analytical model are developed to predict the actuation profile, both showing excellent agreement with the experimental measurements. The actuation force of the dielectric elastomer actuator is measured as a function of the applied voltage and displacement and estimated using the analytical and numerical models. Finally, a few examples of dielectric elastomers with other designs of the 3D-printed stiffening elements and their actuation shapes are demonstrated.