Ionic Polymer Metal Composite Actuators Research Articles

Fused filament 3D printing of ionic polymer-metal composites (IPMCs)

This paper describes a new three-dimensional (3D) fused filament additive manufacturing (AM) technique in which electroactive polymer filament material is used to build soft active 3D structures, layer by layer. Specifically, the unique actuation and sensing properties of ionic polymer-metal composites (IPMCs) are exploited in 3D printing to create electroactive polymer structures for application in soft robotics and bio-inspired systems. The process begins with extruding a precursor material (non-acid Nafion precursor resin) into a thermoplastic filament for 3D printing. The filament is then used by a custom-designed 3D printer to manufacture the desired soft polymer structures, layer by layer. Since at this stage the 3D-printed samples are not yet electroactive, a chemical functionalization process follows, consisting in hydrolyzing the precursor samples in an aqueous solution of potassium hydroxide and dimethyl sulfoxide. Upon functionalization, metal electrodes are applied on the samples through an electroless plating process, which enables the 3D-printed IPMC structures to be controlled by voltage signals for actuation (or to act as sensors). This innovative AM process is described in detail and the performance of 3D printed IPMC actuators is compared to an IPMC actuator fabricated from commercially available Nafion sheet material. The experimental results show comparable performance between the two types of actuators, demonstrating the potential and feasibility of creating functional 3D-printed IPMCs.

Ionic polymer–metal composite actuators obtained from sulfonated poly(ether ether sulfone) ion-exchange membranes

The cost-effective and high-performance ionic polymer–metal composites (IPMC) were designed and prepared from ion-exchange membranes based on sulfonated poly(ether ether sulfone) (SPEES) with different degrees of sulfonation (DS). The precursor of SPEES, namely PEES, is commercially available and industrial grade. Moreover, the PEES can be transformed easily into ion-conductive SPEES through a simple sulfonation reaction. The ion exchange capacity (IEC) and water uptake (WU) of SPEES membranes increase with increasing their DS, and the proton conductivities of these hydrated SPEES membranes are subsequently enhanced. Compared with the commercial Nafion ion-exchange membrane, the SPEES membranes have higher IEC and WU. The IPMC actuators made of the SPEES membranes show the large bending strain and fast response under electric stimulation. The SPEES membrane with the highest DS (SPEES4) shows the best performance of IPMC actuators. The electromechanical behaviors of these IPMC actuators indicate that the SPEES is a candidate to substitute Nafion.

전기활성 고분자 구동 손가락 외골격 장치의 잡기 성능에 관한 연구

A finger exoskeleton actuated by ionic polymer metal composite (IPMC) actuators has been developed. In order to evaluate performance of cylindrical grasping of finger exoskeletons, they were equipped with a hand dummy, which is composed of four fingers. The finger dummy has three joints that can be actuated by bending the IPMC actuators. A four finger grasping motion was analyzed using cameras, and cylindrical grasping motion was accomplished within two minutes after applying a 4 volt direct voltage to the IPMC actuators. A pull out test was also performed to evaluate the cylindrical grasping force of the finger exoskeletons actuated by the IPMC actuators. Each finger generated about 2 N of holding force when grasping the cylinder which had a diameter of 50 mm.

손가락 외골격용 전기활성 고분자 구동체-센서 하이브리드 구조체의 굽힘 동작 제어

This study was conducted in order to develop a finger exoskeleton system using ionic polymer metal composites (IPMCs) as the actuator and sensor in a hybrid structure. To use the IPMC as an actuator producing large force, a first order transfer function was obtained using results from a block force for DC excitation that applied to two IPMCs of 20mm-width, 50mm-length, and 2.4mm thickness together. After which the validation of 200gf control with anti-windup PI controller was confirmed. A 5mm-width, 50mm-length, 0.6mm-thickness of IPMC was also modeled as a sensor for tip displacement. As a result, the IPMC sensor could been utilized as a trigger role for the actuator. Finally, an IPMC sensor and actuator were installed on the joint of a single DOF exoskeleton in the hybrid structure, and test for the control of 40gf of block force and predefined sequence of motion was performed.

A comprehensive physics-based model encompassing variable surface resistance and underlying physics of ionic polymer-metal composite actuators

The ionic polymer-metal composite (IPMC) is an emerging smart material in actuation and sensing applications, such as artificial muscles, underwater actuators, and advanced medical devices. However, the effect of the change in surface electrode properties on the actuating of IPMC has not been well studied. To address this problem, we theoretically predict and experimentally investigate the dynamic electro-mechanical response of the IPMC thin-strip actuator. A model of the IPMC actuator is proposed based on the Poisson-Nernst-Planck equations for ion transport and charge dynamics in the polymer membrane, while a physical model for the change of surface resistance of the electrodes of the IPMC due to deformation is also incorporated. By incorporating these two models, a complete, dynamic, physics-based model for IPMC actuators is presented. To verify the model, IPMC samples were prepared and experiments were conducted. The results show that the theoretical model can accurately predict the actuating performance of IPMC actuators over a range of dynamic conditions. Additionally, the charge dynamics inside the polymer during the oscillation of the IPMC is presented. It is also shown that the charge at the boundary mainly affects the induced stress of the IPMC. The current study is beneficial for the comprehensive understanding of the surface electrode effect on the performance of IPMC actuators.

Durable electromechanical actuator based on graphene oxide with in situ reduced graphene oxide electrodes

Conventional ionic polymer–metal composite actuator had two major drawbacks: (i) complicated and time-consuming fabrication of noble metal electrode and (ii) degradation of electromechanical property in open air. In this study, we proposed a facile method to fabricate graphene oxide (GO)-based electromechanical actuators with surface-reduced graphene oxide (rGO) as its electrodes. Such GO actuators were fabricated by evaporating the aqueous dispersion of exfoliated GO nanosheets, followed with in situ reduction of the surface of the GO nanosheets by hydrogen iodide (HI). When subjected to a 3 V electrical field, the GO actuator performed electromechanical bending action with a tip displacement of 5 mm and exhibited a blocking force of 10 gf g−1 for 10 s. In addition, the GO actuator showed an almost identical actuating behavior in cyclic measurements. The durable actuation could be attributed to both the unique lamellar structure of the GO film which blocked the diffusion of cationic clusters and the surface rGO electrodes which protected the interlamellar water from evaporation.

A new ionic polymer–metal composite based on Nafion/poly(vinyl alcohol-co-ethylene) blends

The blended ion-exchange membrane of Nafion and poly(vinyl alcohol-co-ethylene) [P(VA-co-E)] was used to fabricate a new type of ionic polymer–metal composite (IPMC). P(VA-co-E) solution was blended in Nafion solution by a volume ratio of 30% and 50% and membranes were prepared through a solution casting method. The blend membranes were characterized by Fourier transform infrared spectroscopy, and differential scanning calorimetry. IPMCs based on these membranes were fabricated by deposition of platinum electrode onto their surface via electroless plating process. The two-point probe measured electrode surface resistance of all prepared IPMCs was less than 2.0 cm−1. We further characterized the cross-sectional morphology and studied the electromechanical performances (displacement and blocking force) of the prepared IPMC actuators. The IPMC actuators with the blended Nafion membranes demonstrated comparable electromechanical performance to the Nafion membrane by significantly reducing the content of Nafion.

The enhancement effect of lithium ions on actuation performance of ionic liquid-based IPMC soft actuators

Soft actuators are of great technological interest and one class of these is made from ionic polymer-metal composites (IPMCs). It has been established that replacement of water with an ionic liquid (IL) in IPMCs results in larger actuation response and considerably longer operating life. However, the rate of displacement of IL-based IPMCs is very low. In the current work, IPMC actuators were fabricated using Nafion membrane and an imidazolium-based IL. The effects of incorporating the IL with and without Li+ ions were followed using electromechanical and electrochemical measurements and were compared with the corresponding behavior of water-based Li+-exchanged and un-exchanged IPMC actuators. The addition of Li+ ions to the IL-based system resulted in dramatic increases in the capacitance, ionic conduction, operating life and in the displacement rate of the actuator. This strategy is of considerable interest for enabling the use of IPMC-based soft actuators in medicine and robotics.

Feasibility Study of Arduino Microcontroller Usage for IPMC Actuator Control

This paper investigates the usage of Arduino microcontroller to control closed loop of IPMC actuator response designed for compact underwater application. We demonstrate control of single Ionic Polymer Metal Composite (IPMC) actuator by PID controller using MATLAB/Simulink Arduino Input Output (ArduinoIO) support package. Experimental results show that the microcontroller able to differentiate response speed and stability of IPMC actuator with different thicknesses. Based on Arduino data acquisition results, thinner IPMC (t1) has more than 5 times respond speed than thicker IPMC (t2). However, IPMC t1 has lower steady-state stability (higher noise) compared to IPMC t2 due to IPMC actuator mechanism factors and current setup limitation for Arduino microcontroller. Therefore, added with further improvements in term of analog read sampling rate and analog write resolution, Arduino microcontroller can accurately control and analyse the IPMC actuator, thus manage to replace expensive and bulky current DAQ hardware.

Accurate Dynamic Modeling of Helical Ionic Polymer-Metal Composite Actuator Based on Intrinsic Equations

This paper presents dynamic modeling of an innovative contractible ionic polymer-metal composites (IPMC) actuator with a helical configuration. The helical shaped IPMC actuator is fabricated through the thermal treatment of an IPMC strip, which is helically coiled on a glass rod. This type of a soft actuator can be used to realize not only bending motion but also torsional and longitudinal motion. For the first time, an explicit analytical expression is developed for the computation of mode shapes and dynamic responses of a helical IPMC actuator based on the intrinsic equations of the naturally curved and twisted beam. The numerical transfer-matrix method is used to solve the systems of 12 linear ordinary differential equations with boundary conditions. In particular, the effect of the structural parameters on the performance of the helical IPMC actuator is evaluated, using experimental results and an analytical model. The validation of the proposed model is achieved through comparison with computational results using a commercial finite-element (FE) program as well as experimental results. The present experimental and theoretical results show that diameter, among the structural parameters, plays an important role in the actuation performance of a helical IPMC actuator. The proposed modeling is general and can also be used in solving other cylindrical or noncylindrical helical IPMC actuators with different cross-sectional shapes as well as various end conditions.

Development of sulfonated poly(vinyl alcohol)/polpyrrole based ionic polymer metal composite (IPMC) actuator and its characterization

In the present study, a novel sulfonated poly(vinyl alcohol)/polypyrrole polymer membrane sandwiched between platinum (SPVA-Py-Pt) is fabricated for a bending actuator which can be used in microrobotic applications. To examine the suitability of SPVA-Py-Pt based ionic polymer metal composite (IPMC) for microrobotic applications, ion exchange capacity (IEC), water uptake, proton conductivity, water loss, cyclic voltammetry (CV), linear sweep voltammetry (LSV), Fourier transform infrared spectroscopy (FTIR), thermal stability, and tip displacement studies are performed. The water holding capacity of the IPMC membrane is found to be 82.23% at room temperature for 8 h of immersion time. The IEC and proton conductivity of the IPMC membrane is found to be 1.2 meq g−1 and 1.6 × 10−3 S cm−1, respectively. Maximum water loss from IPMC is achieved as 31% at 5 V for a time period of 16 min. Based on electromechanical characterization, the maximum tip displacement of SPVA-Py-Pt IPMC (size 30 mm length, 10 mm width, 0.08 mm thickness) is 18.5 mm at 5.25 V. The major advantages of this new type of IPMC are good film-forming capability, short processing time, low cost of fabrication, good flexibility, high thermo-mechanical stabilities, good ion exchange and water holding capacities and proton conductivity as compared to other types of IPMC actuators. The comparison with other type of IPMC actuators is also summarized. A multi SPVA-Py-Pt IPMC based micro-gripping system is developed that shows the potential of microrobotic applications.

Development of the Bending Actuator with Nafion-Pt IPMC Tube

IPMC (Ionic Polymer Metal Composite) is promising candidate actuator for bio-related applications mainly due to its biocompatibility, soft properties and operation in wet condition. In this paper, a new actuator will be presented. The tubular actuator, based on the concept of tip-displacement of IPMC actuator and capable of generating bending of tube with surface outside electrodes, was proposed and studied experimentally. The actuator is a Nafion tube consisting of an even number of Pt segments along the length, which are plated outside of tube surface, and the Pt segments act as electrodes to apply the driving voltage. The experimental data measured on prototype actuators prove the proposed concept of bending depend on the shape of Nafion. Show that the actuator functions well both displacement and force.

Highly Enhanced Force Generation of Ionic Polymer-Metal Composite Actuators via Thickness Manipulation.

On purpose to enhance the generating force of ionic polymer-metal composite (IPMC) actuators, the thickness of the ion-exchange membrane is manipulated in two different ways. One is grafting poly(styrenesulfonic acid) onto poly(vinylidene fluoride-co-hexafluoropropylene) films with varying thickness, and the other is stacking pre-extruded Nafion films to thicker films by pressing at high temperatures. For both groups of the membranes, ionic properties including ion-exchange capacity and ionic conductivity are maintained similarly inside the groups regardless of the thickness. The actuation tests clearly show the increase in generating force with increasing thickness of the IPMCs prepared. It is due to a larger bending stiffness of thicker IPMCs, which is consistent with the predicted result from the cantilever beam model. The increase in force is more remarkable in Nafion-stacked IPMCs, and a thick IPMC lifts a weight of 100 g, which far exceeds the reported values for IPMCs.

Slender tube-shaped and square rod-shaped IPMC actuators with integrated sensing for soft mechatronics

This paper describes the development of slender millimeter-size hollow (tube) and sub-millimeter-size solid (rod) shaped ionic polymer-metal composite (IPMC) actuators. The outer electrodes on the IPMC actuators are sectored to enable control for multiple degrees of freedom motion. Such small-size slender (high aspect ratio) IPMC actuators can be used to create active catheter devices, bio-inspired propulsion mechanisms in underwater autonomous systems, artificial cilia structures for micro-fluidic devices, and other emerging soft mechatronic systems. An experimental tube-shaped IPMC actuator is fabricated from Nafion polymer tube with inner and outer diameters of 1.3 and 1.6 mm, respectively. Likewise, the fabrication of a sub-millimeter size square cross-section rod IPMC actuator is described, with dimensions of 150 μm by 150 μm and 500 μm by 500 μm. The outer surface of the IPMC actuators are plated with platinum metal via an electroless plating process. The platinum plating is sectored into four isolated electrodes using a custom surface milling technique. Independent control of the patterned electrodes on the outer surface of the tube results in three-dimensional motion. A strain sensor is developed and integrated with the tube-shaped IPMC to sense the bending motion of the actuator as an example of its functionality. The integrated sensor is low cost and avoids the need for bulky external sensors such as lasers for measuring deflection. Thus, the sensor can be employed in practical applications including feedback control. The actuators are characterized and experimental results are presented to demonstrate performance.

Reliability tests of ionic polymer metallic composites in dry air for actuator applications

Electroactive polymers (EAPs) are capable of exhibiting large shape changes in response to electrical stimulation. EAPs can produce a large deformation with a low applied voltage for actuation applications. The IPMC (Ionic Polymer Metal Composite) is a well-known type of ionic EAP. It has numerous attractive advantages, such as low electrical energy consumption and being lightweight. The underlying mechanism of an IPMC actuator is the ionic diffusion when a voltage gradient is applied. As such, the characteristics of the ionic solution have a large impact on the physical properties of the IPMC. In this paper, reliability tests of IPMCs with a non-aqueous ionic solution are demonstrated. The Pt-IPMC with LiOH aqueous solution exhibits the best maximum displacement, but the water in the LiOH solution is electrolyzed easily because of the low electrolysis voltage (1.23V) of water. To ameliorate the electrolysis problems and improve the operation time, more appropriate solvents with a high electrolysis voltage and low vapor pressure should be chosen. Parylene-coating can also protect the IPMC from solvent loss. The reliability tests focus on the durability of IPMCs in dry air. Improvements in IPMC fabrication, such as Ag-IPMC, are discussed in this paper. Through the use of parylene protection and an ionic solution with a high electrolysis voltage, the lifetime of the Ag-IPMC in dry air is up to 15 times greater than that of the uncoated Ag-IPMC with aqueous solution. We have addressed potential issues regarding the dry air actuation of IPMCs, and found that the cracking of electrodes has a major impact on the reliability of the IPMCs in this study.

A Comprehensive Review of the Biomimetic Applications of Ionic Polymer Metal Composite

Bio-inspiration focuses on translating the evolutionary successes of natural species into engineering systems that mimic the geometry, function, and performance of the natural system. In this paper we present a latest comprehensive review of ionic polymer metal composite (IPMC) biomedical and biomimetic applications. IPMC is becoming an increasingly popular material among scholars, engineers and scientists due to its inherent properties of low activation voltage, large bending strain, flexibility, softness, suitable response time which make them a strong candidate to be applied as artificial muscle in biomimetic land and underwater applications. Among the diversity of electro active polymers (EAPs), recently developed IPMCs are good candidates for use in bio-related application because of their biocompatibility. Several recently reported IPMC biomimetic applications have been reported in this paper. The applications of IPMC have been growing due to progression in its manufacturing techniques, development of more accurate response models and control techniques, and recently more sophisticated IPMC actuator applications have been performed. This indicates that the IPMC actuators hold potential for more sophisticated and controlled applications in fields of biomedical and biomimetic. Extensive references are provided for more indepth explanation.

A Compact Ionic Polymer Metal Composite (IPMC) System with Inductive Sensor for Closed Loop Feedback

Ionic polymer metal composite (IPMC), of which a low actuating voltage (<5 V), high power efficiency and biocompatibility makes it a proven candidate for low power devices. However, due to its inherent nonlinear behaviour and time-variance, feedback control, as well as reliable sensing means, are required for accurate operations. This paper presents an IPMC actuator implemented with an inductive sensor to enhance the reliability and compactness of the overall device. A practical, low cost and importantly, compact inductive sensor fabricated on a printed circuit board (PCB) is proposed here. Target material selections and coil design considerations are discussed. It is experimentally determined that the inductive sensor has comparable performance to a laser sensor. Based on a proportional-integral-derivative (PID) control results the inductive sensor has demonstrated to be an alternative to a laser sensor allowing devices using IPMC actuators to be compact.

Development and evaluation of a Venus flytrap-inspired microrobot

Nature has provided the inspiration for many robots, leading to the development of biomimetic machines based on stick insects, jellyfish, butterflies, lobsters, and inchworms. Some carnivorous plants are capable of rapid motion, including mimosa, Venus flytraps, telegraph plants, sundews, and bladderworts, all of which are of interest in the design of biomimetic robots that can be activated in a controlled manner to capture prey using trigger hairs. Here, we describe a biomimetic robotic inspired by a Venus flytrap and fabricated using two ionic polymer metal composite (IPMC) actuators. First, we describe the structure of the robotic flytrap, which consists of two IPMC lobes and a proximity sensor, and discuss the design of the control circuitry. We then evaluate the deformation and bending force of the IPMC actuator with various applied signal voltages. We describe a prototype robotic flytrap utilising a proximity sensor to imitate the trigger hairs of the Venus flytrap. We conducted an experiment to assess the feasibility of the biomimetic flytrap. To evaluate grasping ability, we measured the maximum grasping payload with different applied voltages. To enlarge the working area, we integrated biomimetic walking and rotating motion into the robotic Venus flytrap. This paper describes a prototype movable robotic Venus flytrap and evaluates its walking and rotating speeds.

The sliding mode control for different shapes and dimensions of IPMC on resisting its creep characteristics

Ionic polymer metal composite (IPMC) is a novel smart material which has been widely implemented in MEMS, biomimetic mechanical and electrical integrated system and micro operation system. While the IPMC with different shapes and dimensions has been implemented in many different types of biomechanical integrated systems, one of its inherent properties called creep characteristic is difficult to be handled, which limits the further application of different IPMCs in integrated systems. A promising control method called sliding mode control (SMC) is proposed to resist the creep characteristics in this paper. The SMC controller can regulate IPMC actuators with different shapes and dimensions effectively to resist the creep characteristics without changing parameters of the control system. Experiments of four different types of IPMC actuators were conducted on the semi-physical SMC experimental platform. All the experimental results confirm the feasibility of the SMC control approach on regulating the multi-IPMCs with different shapes and dimensions based integrated system.

Characterization of Nafion nanocomposites with spheric silica, layered silicate, and amphiphilic organic molecule and their actuator application

Nafion nanocomposite membranes with spheric silica, layered silicate (montmorillonite; MMT), and an amphiphilic organic molecule (10-camphorsulfonic acid; CSA) have been investigated as polyelectrolytes for ionic polymer-metal composite (IPMC) actuators. An organosilane (3-mercaptopropyltrimethoxy silane; 3-MPTMS) was grafted on the surfaces of silica and MMT, and the thiol groups on the fillers were sulfonated to endow them with additional hopping sites. The incorporation and modification of the fillers in the Nafion matrix greatly altered the internal morphologies of hydrophilic ion-rich and hydrophobic fluorocarbon regions, followed by changes in mechanical properties, dimensional stabilities, and mass transport kinetics. Finally, the Nafion nanocomposite membranes were engaged as the polyelectrolytes of an IPMC actuator, and actuation performance was analyzed, being associated with the internal morphology-driven diffusion characteristics and capacitances in the polyelectrolyte membranes and the resulting efficiency of charge-to-deformation.