Ionic Polymer Metal Composite Research Articles

Fast actuation properties of several typical IL-based ionic electro-active polymers under high impulse voltage

Slow deformation is an issue that restrains engineering applications of ionic electroactive polymers (EAP). The application of a high impulse voltage has been proposed to accelerate the deformation of water based ionic polymer-metal composites (IPMC). In this paper, focused on ionic liquid (IL) based ionic EAPs, ionic polymer carbon composites (IPCC), IL–IPMC, ionic and capacitive laminates, and bucky gel actuators were selected to verify the effectiveness of the high impulse voltage method. All four were able to be accelerated more than tenfold under high impulse voltages. To investigate the limitations of the high impulse voltage method, constant pulse width measurements were performed on IPCC and IL–IPMC. The deformation speed was almost linear with the pulse amplitude before it reached the maximum deformation. On setting a constant pulse width, a large deformation and a higher speed could be obtained by increasing the pulse amplitude. Additionally, by fixing the pulse amplitude, extending the pulse width induced a larger deformation at a certain speed. Finally, the consumption power and heat issues were investigated via cycling tests. A shorter cycle time (higher frequency) and a higher pulse amplitude led to larger power consumption and higher temperature. The ionic EAPs damaged at high temperature (usually over 100 °C), which is probably due to the positive feedback between Joule heating and ion mobility. In addition to the pulse width, the pulse frequency and amplitude require carefully control when using a high impulse voltage.

A Miniature Robotic Turtle With Target Tracking and Wireless Charging Systems Based on IPMCs

State-of-the-art autonomous micro-robotic turtles suffer from various limitations, such as power restrictions that minimize their deployment times. In this paper, an Ionic Polymer Metal Composite (IPMC) actuator-based centimeter-level biomimetic underwater robot was designed and developed as a robotic turtle with self-charging capabilities to overcome such limitations. It could move forward and make turns driven by five IPMCs on the water. The underwater charging station was able to transmit wideband ultrasonic and electromagnetic fields for electromagnetic induction charging. An ultrasonic communication system with one ultrasonic transmitter and two ultrasonic receivers was first fabricated to implement communication between the underwater station and the biomimetic underwater robot for autonomous tracking and rechargeable capabilities. Experiments were carried out to confirm the operation of the biomimetic underwater robot, which verified the centimeter-level rechargeable capabilities and autonomous target tracking features. The micro-robot demonstrated a self-tracking radial displacement error of approximately 6 mm and a charging reliability rate of more than 73%.

Challenges and Perspectives in Control of Ionic Polymer-Metal Composite (IPMC) Actuators: A Survey

Ionic polymer-metal composites (IPMC) are electroactive polymers expected to be used as soft actuators in various practical areas like robotics, biomedicine and micro manipulation systems. Though IPMC actuators have many advantages (lightweight, noiseless operation, low operating voltage, possibility of miniaturization), some of their inherent properties (back-relaxation, hysteresis, high sensitivity to ambient conditions, aging) make their precise and reliable control a challenging task. This paper presents a survey of control methods for IPMC actuators. A systematic overview of the techniques, addressing the main challenges in IPMC control, is provided.

Analysis and Study of the Nonlinear Electrodynamics Behaviour of a Micro-beam Made of Ionic Polymer Metal Composite (IPMC)

Ionic Polymer Metal Composites (IPMCs) are a group of electroactive polymer materials that exhibit a large deformation due to the application of low voltages resulting from the movement of cations inside the polymer. These materials have many applications in various fields such as Micro-robotics, biomedical engineering equipment and artificial muscles. Due to the possibility of producing these materials in micro dimensions they can also be used in micro-electromechanical systems. On the other hand, due to their sensitivity to very low voltages, they can be a good substitute for silicon in micro-electromechanical systems. In the present study, the dynamical analysis of a micro-beam fixed at two ends made of these materials is investigated using electrical-chemical-mechanical relations. COMSOL Multiphysics software is used to solve the relations. The results showed that for harmonic stimulation (sinusoidal voltage) the system experiences only the same form of the first mode. It was also observed that increasing the frequency would decrease the amplitude of the micro-beam oscillation.

High‐Performance Ionic‐Polymer–Metal Composite: Toward Large‐Deformation Fast‐Response Artificial Muscles

AbstractAs promising candidates in the field of artificial muscles, ionic‐polymer–metal composites (IPMCs) still cannot simultaneously provide large deformations and fast responses, which has limited their practical applications. In this study, to overcome this issue, a Nafion‐based IPMC with high‐quality metal electrodes is fabricated via novel isopropanol‐assisted electroless plating. The IPMC exhibits a large tip displacement (35.3 mm, 102.3°) under a low direct‐current driving voltage and ultrafast response (>10 Hz) under an alternating‐current (AC) voltage. Furthermore, the simultaneous integration of a large deformation and fast response can be achieved by the IPMC under a high‐frequency (19 Hz) AC voltage, where the largest bending amplitude is 5.9 mm and the highest bending speed reaches 224.2 mm s−1 (596.2° s−1). Additionally, the lightweight IPMC exhibits a decent load capacity and can lift objects 20 times heavier. The outstanding performances of the Nafion IPMC are demonstrated by mimicking biological motions such as petal opening/closing, tendril coiling/uncoiling, and high‐frequency wing flapping. This study paves the way for the fabrication of lightweight actuators with simultaneous large displacements and fast responses for promising applications in biomedical devices and bioinspired robotics.

A Compact Review of IPMC as Soft Actuator and Sensor: Current Trends, Challenges, and Potential Solutions From Our Recent Work.

Recently, attempts have been made to develop ionic polymer–metal composite (IPMC), which is garnering growing interest for ionic artificial muscle, as a soft actuator and sensor due to its inherent properties of low weight, flexibility, softness, and particularly, its efficient transformation of electrical energy into mechanical energy, with large bending strain response under a low activation voltage. In this paper, we focused on several current deficiencies of IPMC that restrict its application, such as non-standardized preparation steps, relaxation under DC voltage, solvent evaporation, and poor output force. Corresponding solutions to overcome the abovementioned problems have recently been proposed from our point of view and developed through our research. After a brief introduction to the working mechanism of IPMC, we here investigate the key factors that influence the actuating performance of IPMC. We also review the optimization strategies in IPMC actuation, including those for preparation steps, additive selection for a thick casting membrane, solvent substitutes, water content, encapsulation, etc. With consideration of the role of the interface electrode, its effects on the performance of IPMC are revealed based on our previous work. Finally, we also discuss IPMCs as potential sensors theoretically and experimentally. The elimination of the deficiencies of IPMC will promote its applications in soft robotics.

Soft Crawling Robots: Design, Actuation, and Locomotion

AbstractSoft crawling robots have attracted great attention due to their anticipated effective interactions with humans and uncertain environments, as well as their potential capabilities of completing a variety of tasks encompassing search and rescue, infrastructure inspection, surveillance, drug delivery, and human assistance. Herein, a comprehensive survey on recent advances of soft crawling robots categorized by their major actuation mechanisms is provided, including pneumatic/hydraulic pressure, chemical reaction, and soft active material‐based actuations, which include dielectric elastomers, shape memory alloys, magnetoactive elastomers, liquid crystalline elastomers, piezoelectric materials, ionic polymer–metal composites, and twisted and coiled polymers. For each type of actuation, the prevalent modes of locomotion adopted in representative robots, the design, working principle and performance of their soft actuators, and the performance of each locomotion approach, as well as the advantages and drawbacks of each design are discussed. This review summarizes the state‐of‐the‐art progresses and the critical knowledge in designing soft crawling robots and offers a guidance and insightful outlook for the future development of soft robots.

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.

3D-Printing and Machine Learning Control of Soft Ionic Polymer-Metal Composite Actuators

This paper presents a new manufacturing and control paradigm for developing soft ionic polymer-metal composite (IPMC) actuators for soft robotics applications. First, an additive manufacturing method that exploits the fused-filament (3D printing) process is described to overcome challenges with existing methods of creating custom-shaped IPMC actuators. By working with ionomeric precursor material, the 3D-printing process enables the creation of 3D monolithic IPMC devices where ultimately integrated sensors and actuators can be achieved. Second, Bayesian optimization is used as a learning-based control approach to help mitigate complex time-varying dynamic effects in 3D-printed actuators. This approach overcomes the challenges with existing methods where complex models or continuous sensor feedback are needed. The manufacturing and control paradigm is applied to create and control the behavior of example actuators, and subsequently the actuator components are combined to create an example modular reconfigurable IPMC soft crawling robot to demonstrate feasibility. Two hypotheses related to the effectiveness of the machine-learning process are tested. Results show enhancement of actuator performance through machine learning, and the proof-of-concepts can be leveraged for continued advancement of more complex IPMC devices. Emerging challenges are also highlighted.

Modeling the actuation and sensing behavior of an IPMC within the framework of the Theory of Porous Media

AbstractElectroactive polymers (EAPs) are considered as smart materials. Therein, a differentiation between an electric and an ionic EAP will be made. In this contribution, in particular the ionic polymer‐metal composites (IPMCs) are investigated which belong to the class of the ionic EAPs. These kind of materials act as an actuator and a sensor in variety of applications. The actuation application is given by applying an electrical voltage to the electrodes which instantaneously leads to the relocation of the mobile cations towards the cathode. The sensor application is performed by loading the IPMC mechanically which generates an electrical field. For the prediction of the behavior of this material, the theoretical framework of electrodynamics in combination with the Theory of Porous Media has been taken into account, see [1–3]. A numerical example for the 2D sensing behavior is investigated.

Characterization of smart materials requirements for actuation in the robotic applications

This paper presents the requirements specification of artificial muscles based on smart materials for a robotic finger prosthesis. The first part introduces the robotic finger, designed to mimic human precision grasping. A methodology to determine three critical parameters (strain, frequency and force) is presented. The methodology uses experimental data combined with kinematics and dynamics. Obtained values are calculated using the developed finger; as a result, we define that main requirements are: (i) Minimum active strain 5.5% for extension-based actuation or 60% bending-based actuation, (ii) Frequency (8.89 Hz, 22.2 Hz), and (iii) Force (4.80 N, 6.74 N) for bending-based actuation or force (17.81 N, 25.11 N) for extension-based actuation. Finally, a review of smart materials is presented with the aim of choosing the group of materials that can be used as artificial muscles for robotic hands. We show that shape memory Alloys can fulfill the established specifications. We also stand out Ionic polymer metal composites as a very promising actuation solution for robotic hands, due to their active strain and settling time, even though the blocking force is below the requirements.

Design and Modeling of a New Biomimetic Soft Robotic Jellyfish Using IPMC-Based Electroactive Polymers.

Smart materials and soft robotics have been seen to be particularly well-suited for developing biomimetic devices and are active fields of research. In this study, the design and modeling of a new biomimetic soft robot is described. Initial work was made in the modeling of a biomimetic robot based on the locomotion and kinematics of jellyfish. Modifications were made to the governing equations for jellyfish locomotion that accounted for geometric differences between biology and the robotic design. In particular, the capability of the model to account for the mass and geometry of the robot design has been added for better flexibility in the model setup. A simple geometrically defined model is developed and used to show the feasibility of a proposed biomimetic robot under a prescribed geometric deformation to the robot structure. A more robust mechanics model is then developed which uses linear beam theory is coupled to an equivalent circuit model to simulate actuation of the robot with ionic polymer-metal composite (IPMC) actuators. The mechanics model of the soft robot is compared to that of the geometric model as well as biological jellyfish swimming to highlight its improved efficiency. The design models are characterized against a biological jellyfish model in terms of propulsive efficiency. Using the mechanics model, the locomotive energetics as modeled in literature on biological jellyfish are explored. Locomotive efficiency and cost as a function of swimming cycles are examined for various swimming modes developed, followed by an analysis of the initial transient and steady-state swimming velocities. Applications for fluid pumping or thrust vectoring utilizing the same basic robot design are also proposed. The new design shows a clear advantage over its purely biological counterpart for a soft-robot, with the newly proposed biomimetic swimming mode offering enhanced swimming efficiency and steady-state velocities for a given size and volume exchange.

Review of Soft Actuator Materials

Soft actuator materials change their shape or size in response to stimuli like electricity, heat, light, chemical or pH. These actuator materials are compliant and well suited for soft mechatronics and robots. This paper introduces the definition of soft materials and the position of soft actuator materials in comparison with conventional actuators and other solid state actuator materials. A thorough review of selected soft actuator materials is carried out, including responsive gels/hydrogels, ionic polymer metal composites, conducting polymers, carbon nanotubues/graphenes, dielectric elastomers, shape memory polymers and biopolymers. This review will give insights for applications of soft actuator materials via better understanding of the materials in terms of their preparation, performance and limitation.

A novel crenellated ionic polymer-metal composite (IPMC) actuator with enhanced electromechanical performances

Ionic polymer-metal composite (IPMC) is a promising biomimetic actuator that has received significant attention due to its remarkable high-strain electromechanical performances under low stimulated voltage. Most importantly, it is able to operate in aqueous environment. Nonetheless, the actuation force of the IPMC deteriorates when the applied strain gets too large, which has limited its applications practically. This work has introduced a novel approach that can be used to design crenellated structure on an IPMC actuator for improving its mechanical strength. Numerical simulation has been conducted to optimize the crenellate ratio for achieving larger blocking force and tip deflection. Experimental data has confirmed that the IPMC with the crenellate ratio of 2:3 can improve the blocking force as much as ∼70% and the tip deflection for at least 360%, being much better than the non-crenellated IPMC structure. Dynamic tests were performed at 1 Hz frequency to validate the actuator’s operation in water and air media. The newly proposed crenellated structure can improve the IPMC performances significantly, and it will surely broaden the range of possible applications of the IPMC actuator.

Ionic polymer-metal composites actuator driven by the pulse current signal of triboelectric nanogenerator

Ionic polymer-metal composites (IPMCs), a kind of electroactive polymer, have been considered as artificial muscle due to their deformation in response to electrical stimulation. However, the needing of external power supply severely limits IPMC's wide applications. Herein, newly developed energy harvesting technique of triboelectric nanogenerator (TENG) is used to directly drive IPMC, in order to establish a self-powered actuation system. Even though IPMC cannot utilize the voltage signal from TENG, it is possible for IPMC to accumulate the transferred charge from several motion cycles of TENG. Hence, the combined TENG-IPMC system also develops a new approach for utilizing the current signal from TENG as the control signal. Comparing with IPMC under the drive of power source, TENG-IPMC system needs much lower (about 0.1%) transferred charges to achieve the same bending angle than that of DC power. The actuation of TENG-IPMC system can be controlled precisely through the design of TENG, which can be utilized for several intelligent electromechanical applications, including self-powered gripper, tunable laser projector, and soft robotic in liquid. The TENG-IPMC system has many advantages, such as high energy conversion rate, small size, and low cost, which will significantly improve the usability and portability of IPMC.

Sensing mechanical deformation via ionic polymer metal composites: A primer

Ionic polymer metal composites (IPMCs) were discovered about twenty five years ago by Prof. Oguro and his team in Japan [1], and evidence about metalizing ionomer membranes dates even earlier [2]. Since their discovery, IPMCs have been the object of intensive research across the entire globe [3]-[5]. In its simplest form, an IPMC is constituted by a hydrated ionomeric membrane (that is, an electrically-charged polymer), which is neutralized by mobile counterions in a solution and plated by noble metal electrodes. IPMCs can be used as actuators and sensors, whereby a voltage applied across the electrodes will elicit mechanical deformation, and an imposed mechanical deformation will induce a measurable voltage across the electrodes.

Adaptive Microtracking Control for an Underwater IPMC Actuator Using New Hyperplane-Based Sliding Mode

The ionic polymer metal composite (IPMC) actuator is one of the most promising smart actuators that possesses unique advantages and is suitable for underwater applications. However, there are challenges to employ it directly in such applications for precise tracking. The IPMC suffers from high nonlinearity due to the existence of inherent creep and hysteresis phenomena. Furthermore, the IPMC actuator is always subject to uncertainty and external disturbance due to the working environment. Therefore, to cope with the aforementioned restrictions and to make the IPMC applicable for real-life applications, designing a high-accuracy tracking control technique is an urgent demand. In this article, a new integral nonlinear hyperplane-based sliding mode controller is dedicated for an underwater IPMC actuator. The proposed controller employs an adaptive tuning law in the discontinuous part to overcome any prerequisite for knowing the upper bound of the model uncertainty and external disturbance. Extensive experiments have been carried out to verify practical effectiveness of the proposed controller in comparison with conventional nonsingular terminal sliding mode in terms of fast convergence, accurate tracking, and the robust performance.

Fundamentals and applications of ion migration induced polymer sensor detecting bending, pressure and shear force

Electric potential induced by ion migration exists widely in organisms such as tactile corpuscles and auditory hair cells. Mechanosensitive ion channels open under the influence of stretch, pressure, shear, and displacement. As shown in Fig. 1, cell membrane potential is generated by ion transport through the phospholipid bilayer, which is the basis for our tactile and auditory sensing [1], [2]. Similar to these cells, ion-migration induced electricity can be realized by ionic electro-active polymers (iEAP), which include ionic gel, ionic polymer-metal composites (IPMC), bucky gel actuator and conducting polymers, etc. Because of their advantages of light weight, low modulus of elasticity (20-300 MPa) and low mechanical / acoustic impedance (2 Mkg/(m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> s)), they can be used as flexible sensors and have wide potential application in biomimetic sensors such as artificial skin, artificial lateral lines and artificial ears.

The evolution of ionic polymer metal composites towards greener transducers

The implementation of Industry 4.0 and IoT will require the availability of large-mass production electronics. The infusion of intelligence, required for realizing smart grids, cities, homes, and cars, just to mention a few, will encourage the ubiquitous diffusion of electronics in everyday life. Think, e.g., to the evolution of cellular phone complexity, or of smart domestic appliances. The need for intelligent applications will not be limited to our cities or homes. Precise agriculture will, e.g, require a massive diffusion of smart devices, which will be required for monitoring the wellness of each plant. In a similar way, smartness is required for the continuous monitoring of the healthiness and safety of large infrastructures such as dams or viaducts, just to mention a few.

Fabrication and performance of ionic polymer-metal composites for biomimetic applications

Ionic Polymer-Metal Composites (IPMCs) consisting of ionic polymer membrane sandwiched between platinum and copper (Cu-Pt) electrodes have been synthesized via electroless plating and electroplating. The tip displacement of Cu-Pt coated IPMC reached about 10.7 mm when a sinusoidal potential of 3V, 0.6Hz was applied through the membrane. The surface roughness of Pt coated IPMC, Cu-Pt coated IPMC and Cu-Pt coated IPMC after bending deformation tests were 1.21, 0.77 and 0.71 μm respectively, indicating that Cu electrode could reduce surface roughness. It was also found that a new generated Cu layer healed the cracks of Pt electrode, was formed through using voltage polarity. Butyl rubber and polydimethysiloxane (PDMS) were employed to encapsulate Cu-Pt coated IPMC to prevent Cu electrode from oxidation. The output deformation of packaged Cu-Pt coated IPMCs were stable under various amplitude of potential. The deflection of Cu-Pt coated IPMCs kept in air for 3, 7, 15 and 22 days respectively had no significant changes and were all about 10.1 mm by applying the potential of 3V, 0.6Hz, revealing that Cu electrode is durable and Cu-Pt coated IPMCs exhibit remarkable promise as biomimetic actuators.