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Electrotactile stimulation is a highly promising technique for providing sensory feedback information for prosthetics. To this aim, disposable electrodes which are predominantly used result in a high environmental and financial cost when used over a long period of time. In addition, disposable electrodes are limited in their size and configurations. This paper presents an alternative approach based on a 3D printed reusable flexible concentric electrode coated with a conductive graphene ink. Here, we have characterized the electrode and demonstrated its effective performance in electrotactile stimulation and sensory feedback for robotic prosthetic hands.

An effective method of communicating sensory feedback for prosthetics is presented using a combination of mechanical pressure and skin stretch, resulting in a mixture of normal and shear force being applied to the human arm. Stimulations were induced on the subject's forearm by three mechanical cranks, each attached to their own servo motor. Three different crank orientations were tested, each producing a different skin stretch direction, with the results showing that shear force/tangential skin stretch applied longitudinally to the forearm was perceived more easily as it produced the best recognition rate. With minimal training, eighteen able-bodied test subjects were able to recognise six different grips with an accuracy of up to 88%, and achieved an accuracy of 80% when recognising the six grips at two different pressure levels. This sensory feedback mechanism shows potential for a simple, easy to learn stimulation device that could help improve users control and embodiment of their prosthetic device that requires three separate feedback channels.

One of the challenging research questions in soft robotics is the establishment of valid mathematical models and control techniques under limited feedback conditions. A soft robotic system will typically have a continuum or monolithic body seamlessly embodying its actuation and sensing elements, accompanied by mechanical structure, and even the energy source, much like a biological system. In this study, we propose a relay sliding mode controller based on the input - output model (RSMC-IO), which is a simple but effective control approach that does not require a complete system model, to control the tip position of a soft prosthetic finger, which typifies a monolithic soft robotic positioning system. The feedback signal corresponding to the bending angle of each joint of the finger is provided by highly stretchable soft strain sensors made of a silicone (EcoFlex 0010) substrate containing channels filled with carbon paste as the conductive component. An analytical expression between the fingertip and joint angles of the finger is derived and experimentally verified. This expression is accurate enough to estimate the joint positions (i.e. joint angles) as well as the fingertip. The experimental results show the efficacy of the proposed controller, which has not been proposed for prosthetic fingers and similar soft robotic positioning systems before.

This study aims to investigate the effects of various design parameters on the actuation performance of a pneumatic network actuator (PNA), optimise its structure using the finite element method (FEM), and subsequently quantify the performance of the resulting actuator topology experimentally. The effects of the structural parameters, including the operation pressure, the wall thickness and the gap between the chambers, bottom layer thickness, and the geometry of the channel cross section, on the deformation and bending angle of the actuator were evaluated to optimise the performance of the pneumatic actuator. A Global Analysis of Variance (ANOVA) was performed to investigate how the variables affect the mechanical output of the actuator and, thus, the significance of variables affecting the deformation (and bending angle) of the pneumatic actuator was identified. After the parameter optimisation, a pneumatic channel with a 4.5 mm bottom layer thickness, 1.5 mm wall thickness, and 1.5 mm gap between sequential chambers is recommended to perform optimised bending motion for the pneumatic network actuator. The optimised FE model results were verified experimentally. This design optimisation method based on the FEM and ANOVA analysis can be extended to the topology optimisation of other soft actuators.

Any implant or prosthesis replacing a function or functions of an organ or group of organs should be biologically and sensorily integrated with the human body in order to increase their acceptance with their user. If this replacement is for a human hand, which is an important interface between humans and their environment, the acceptance issue and developing sensory-motor embodiment will be more challenging. Despite progress in prosthesis technologies, 50-60 & #x0025; of hand amputees wear a prosthetic device. One primary reason for the rejection of the prosthetic hands is that there is no or negligibly small feedback or tactile sensation from the hand to the user, making the hands less functional. In fact, the loss of a hand means interrupting the closed-loop sensory feedback between the brain (motor control) and the hand (sensory feedback through the nerves). The lack of feedback requires significant cognitive efforts from the user in order to do basic gestures and daily activities. To this aim, recently, there has been significant development in the provision of sensory feedback from transradial prosthetic hands, to enable the user take part in the control loop and improve user embodiment. Sensory feedback to the hand users can be provided via invasive and noninvasive methods. The latter includes the use of temperature, vibration, mechanical pressure and skin stretching, electrotactile stimulation, phantom limb stimulation, audio feedback, and augmented reality. This paper provides a comprehensive review of the non-invasive methods, performs their critical evaluation, and presents challenges and opportunities associated with the non-invasive sensory feedback methods.

In this article, we have established an analytical model to estimate the quasi-static bending displacement (i.e., angle) of the pneumatic actuators made of two different elastomeric silicones (Elastosil M4601 with a bulk modulus of elasticity of 262 kPa and Translucent Soft silicone with a bulk modulus of elasticity of 48 kPa - both experimentally determined) and of discrete chambers, partially separated from each other with a gap in between the chambers to increase the magnitude of their bending angle. The numerical bending angle results from the proposed gray-box model, and the corresponding experimental results match well that the model is accurate enough to predict the bending behavior of this class of pneumatic soft actuators. Further, by using the experimental bending angle results and blocking force results, the effective modulus of elasticity of the actuators is estimated from a blocking force model. The numerical and experimental results presented show that the bending angle and blocking force models are valid for this class of pneumatic actuators. Another contribution of this study is to incorporate a bistable flexible thin metal typified by a tape measure into the topology of the actuators to prevent the deflection of the actuators under their own weight when operating in the vertical plane.

Robotic systems consisting of rigid elements connected to each other with single degree of freedom joints have been studied extensively. Robotic systems made of soft and smart materials are expected to provide a high dexterity and adaptability to their physical environment, like their biological counterparts. Electroactive polymer (EAP) actuators, also known as artificial muscles, which can operate both in wet and in dry environments with their promising features such as a low foot-print in activation and energy consumption, suitability to miniaturization, noiseless, and fully compliant operation can be employed to articulate a soft robotic system. This paper reports on kinematic modeling of a polypyrrolebased EAP actuator which is designed and fabricated to form helical configurations in 3-D from its initially spiral 2-D configuration. Denavit-Hartenberg transformations are combined with the backbone model of the actuator to establish the kinematic model. A parametric model has then been incorporated into the kinematic model to accurately estimate the helical configurations of the EAP actuator as a function of time under an electrical input. Experimental and simulation results, which are in good correlation, suggest that the proposed modeling approach is effective enough to estimate the 3-D helical configurations of the EAP actuator.

Soft robotics, as a multi-disciplinary research area, has recently gained a significant momentum due to offering unconventional characteristics relative to rigid robots such as a resilient, highly dexterous, compliant and safer interaction with humans and their physical environments. However, soft robots suffer from not being able to carry their own weight which mainly depends on the modulus of elasticity of the material used to fabricate them. In this paper, we report on a practical and easy-to-implement stiffness augmentation method to enhance stiffness of soft robotic components. We fabricated a soft robotic finger which is fully compliant with flexure hinges using Fused Deposition Modelling (FDM) technique and a stiffness augmenting unit made of thin poly(vinyl chloride)(PVC) sheets. The stiffness of the entire robotic finger was increased mechanically by linearly driving the stiffness augmenting unit. The experimental data presented show that stiffness of the finger was increased by 40 %. Depending on the material properties and thickness used for fabricating the stiffness augmenting unit, a higher rate of stiffness increase can be easily obtained.

As a natural result of the continual growth and progress in soft robotics to establish fully compliant bodies primarily made of soft materials using additive manufacturing techniques, there are also increasing efforts towards realizing flexible and stretchable sensors which can seamlessly be embedded in soft robotic devices. In this study, we report on the performance evaluation of two soft strain sensors based on different fabrication techniques and soft materials. We fabricated one of them in a laboratory environment using a silicone rubber substrate (EcoFlex 0010) engraved with microchannels, which were filled with liquid carbon black (CB). The other one is a commercially available sensor (flexible stretch sensor, Images SI) made of a polymer which changes its resistance when stretched. The electromechanical responses and strain sensing performances of these two sensors are experimentally quantified and their usefulness in practical soft robotics applications is discussed. Although both sensors display a similar strain sensing performance, the commercial sensor is durable over a longer period of time while the microfluidic silicone sensor has a much smaller time constant, making it more suitable for applications with rapidly changing inputs.

Smart actuators have a considerable potential to articulate novel mechanisms and mechatronic devices inspired from biological systems. Electroactive polymer actuators (EAPs), as a class of smart and soft actuators, are ideal candidates for bioinspired mechatronic applications due to their compliance and built-in actuation ability originating from the material they are made of. In this paper, we report on a soft mechatronic mechanism, like a positioning stage, fabricated from bending-type EAP actuators as a one-piece fully compliant mechanism inspired from twining structures in nature. We have employed a quasi-static finite-element model combined with a soft robotic kinematic model to estimate the mechanical output of the soft mechatronic mechanism as a function of a single electrical input. Experiments were conducted under a range of electrical step inputs (0.25-1 V) and sine-wave inputs with various frequencies to validate the models. Experimental and simulation results show that this electrically stimulated soft mechatronic mechanism generates a linear displacement as large as 1.8 mm under 1 V out of its fabrication plane like a lamina emergent mechanism, while its bioinspired spiral parts bend and twine. This fully compliant and compact mechanism can find a place in optics as a microstage and/or an optical zoom mechanism.

This chapter focuses on device configurations based on conjugated polymer transducers. After the actuation and sensing configurations in the literature are presented, some successful device configurations are reviewed, and a detailed account of their operation principles is described. The chapter is concluded with critical research issues. With reference to the significant progress made in the field of EAP transducers in the last two decades, there is an increasing need to change our approach to the establishment of new device configurations, novel device concepts, and cutting-edge applications. To this aim, we should start from the performance specifications and end up with the material synthesis conditions and properties which will meet the performance specifications (top-to-down approach). The question should be “what electroactive material or materials can be used for a specific purpose or application,” rather than looking for an application or a device concept suitable to the unique properties of the EAPs and transducers already made of these materials. The field is mature enough to undertake this paradigm change.

Mechanical compliance is one of the primary properties of structures in nature playing a key role in their efficiency. This study investigates a number of commonly used flexure hinges to determine a flexure hinge morphology, which generates large displacements under a lowest possible force input. The aim of this is to design a soft and monolithic robotic finger. Fused deposition modeling, a low-cost 3D printing technique, was used to fabricate the flexure hinges and the soft monolithic robotic fingers. Experimental and finite element analyses suggest that a nonsymmetric elliptical flexure hinge is the most suitable type for use in the soft monolithic robotic finger. Having estimated the effective elastic modulus, flexion of the soft monolithic robotic fingers was simulated and this showed a good correlation with the actual experimental results. The soft monolithic robotic fingers can be employed to handle objects with unknown shapes and are also potential low-cost candidates for establishing soft and one-piece prosthetic hands with light weight. A three-finger gripper has been constructed using the identified flexure hinge to handle objects with irregular shapes such as agricultural products.

This study reports on the fabrication and response characterisation of highly stretchable strain sensors made of two commercially available silicone rubber substrates (EcoFlex 0010, and Shin-Etsu KE-441-T) engraved with microchannels, which are filled with two conductive liquids; carbon nanofibers (CNF) in poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) dispersion (PEDOT:PSS) and liquid carbon black (CB). We experimentally quantified the electromechanical response and strain sensing performance of the sensors using the metrics of linearity, hysteresis, resolution, transient properties and repeatability. We conclude that while changing the conductive liquid mainly affects the overall resistance of the sensors, the sensors made of EcoFlex have (i) overall much faster response characteristics during both loading and unloading cycles, (ii) less hysteresis, and (iii) a smaller time constant, that makes them more suitable to applications in which the input stimulus changes at a fast rate.

Soft robotics, as a new dimension in robotics, is an rapidly growing research area. Fully compliant mechanisms and structures can be built using soft materials. Having a fully compliant system -a monolithic body- will reduce the manufacturing and assembly costs and show a whole-body bending performance similar to its natural counter-parts. Current prosthetics, particularly fingers and hands, require significant manufacturing and assembly operations. Using additive manufacturing (aka 3D printing), low cost and high performance prosthetic devices can be established. In this study, we report on a fully compliant finger which is 3D printed with a modified low-cost 3D printer based on the Fused Deposition Modelling (FDM) technique. Prior to the finger fabrication, the bending behavior of some well-known flexure hinges were modelled and experimentally evaluated to find the most suitable design for a fully compliant prosthetic finger. Experimental and numerical results from the finite element analysis for the hinges and the complaint finger are in good correlation, encouraging us to establish a single piece prosthetic hand in the near future.

In this paper, a translational actuation mechanism in the form of a parallel-crank mechanism (i.e. double-crank 4-bar mechanism) articulated with two dielectric elastomer actuators working in parallel are fabricated. This structure, which is a fully soft mechanism, is established by stretching a dielectric elastomer (DE) film over a PET (polyethylene terephthalate) frame so that the energy released from the stretched DE film is stored in the frame as bending energy. The mechanism generates a translational output under a driving voltage applied between two electrodes of the DE film. The visco-elastic models are proposed for the mechanism so that the mechanical properties of the actuator can more accurately be incorporated into the mechanism model. The proposed model accurately predicts the experimental frequency response of the mechanism at different voltages.

Electroactive Polymer actuators (EAPs), also known as EAP artificial muscles, offer a great potential for soft robotics. They are suitable for bio-inspired robotic applications due to their built-in actuation property within the mechanical body. In this paper, we report on a fully compliant micro-stage with built-in actuation. It has been fabricated as one piece inspired from twining structures in nature. We have employed a soft robotic modeling approach and finite element modeling to predict the mechanical output of the stage as a function of the input voltage. Experiments were conducted under a range of electrical inputs (0.25-1.00 V). For a given electrical stimulus, the compliant mechanism results in a linear motion in the middle of the active compliant mechanism, as expected. Experiments and simulation results are in good correlation. The active compliant mechanism can be used as a micro stage as well as an optical zoom mechanism for mobile phone cameras and similar devices.

There has been a growing interest in smart actuators typified by conducting polymer actuators, especially in their (i) fabrication, modeling and control with minimum external data and (ii) applications in bio-inspired devices, robotics and mechatronics. Their control is a challenging research problem due to the complex and nonlinear properties of these actuators, which cannot be predicted accurately. Based on an input-shaping technique, we propose a new method to improve the conducting polymer actuators' command-following ability, while minimizing their electric power consumption. We applied four input functions with smooth characteristics to a trilayer conducting polymer actuator to experimentally evaluate its command-following ability under an open-loop control strategy and a simulated feedback control strategy, and, more importantly, to quantify how the type of input function affects the dynamic response of this class of actuators. We have found that the four smooth inputs consume less electrical power than sharp inputs such as a step input with discontinuous higher-order derivatives. We also obtained an improved transient response performance from the smooth inputs, especially under the simulated feedback control strategy, which we have proposed previously [X Xiang, R Mutlu, G Alici, and W Li, 2014 "Control of conducting polymer actuators without physical feedback: simulated feedback control approach with particle swarm optimization', Journal of Smart Materials and Structure, 23]. The idea of using a smooth input command, which results in lower power consumption and better control performance, can be extended to other smart actuators. Consuming less electrical energy or power will have a direct effect on enhancing the operational life of these actuators.

This paper reports on a linear actuation mechanism in the form of a parallel-crank mechanism (i.e., double-crank mechanism) articulated with two dielectric elastomer actuators working in parallel that are fabricated as a minimum energy structure. This structure is established by stretching a dielectric elastomer (DE) film (VHB4910) over a polyethylene terephthalate (PET) frame so that the energy released from the stretched DE film is stored in the frame as bending energy. The mechanism can output a translational motion under a driving voltage applied between two electrodes of the DE film. We have proposed visco-elastic models for the DE film and the frame of the actuator so that the mechanical properties of the actuator can more accurately be incorporated into the mechanism model. The proposed model accurately predicts the experimental frequency response of the mechanism at different voltages. In addition, an inversion-based feedforward controller was successfully implemented in order to further validate the proposed model for sensorless position control of the actuators and the parallel-crank mechanism articulated with these actuators.

Electroactive polymer (EAP) actuators, also known as artificial muscles, have remarkable properties such as low energy consumption, low weight, low actuation foot-print, compliance and bio-compatibility. Several methodologies have been proposed to model and analyse their quasi-static bending behaviour with negligible attention paid to their dynamic behaviour. We, therefore, report on an enhanced methodology to model their highly non-linear bending behaviour by treating them as smart and soft robotic manipulators. The methodology consists of an inverse kinematic model and a dynamic model. The proposed methodology accurately estimates the EAP actuator's whole shape deflection using optimization-based inverse kinematic solutions integrated with an electro-mechanical dynamic model. The experimental and numerical results are presented to show the effectiveness of the soft robotic manipulator model in estimating the highly non-linear bending behaviour of the polypyrrole electroactive polymer (PPy-EAP) actuators. The proposed methodology can easily be extended to other bending type actuators and active smart manipulators. 2014 Elsevier Ltd. All rights reserved.

Conducting polymer actuators have shown significant potential in articulating micro instruments, manipulation devices, and robotics. However, implementing a feedback control strategy to enhance their positioning ability and accuracy in any application requires a feedback sensor, which is extremely large in size compared to the size of the actuators. Therefore, this paper proposes a new sensorless control scheme without the use of a position feedback sensor. With the help of the system identification technique and particle swarm optimization, the control scheme, which we call the simulated feedback control system, showed a satisfactory command tracking performance for the conducting polymer actuator's step and dynamic displacement responses, especially under a disturbance, without needing a physical feedback loop, but using a simulated feedback loop. The primary contribution of this study is to propose and experimentally evaluate the simulated feedback control scheme for a class of the conducting polymer actuators known as tri-layer polymer actuators, which can operate both in dry and wet media. This control approach can also be extended to other smart actuators or systems, for which the feedback control based on external sensing is impractical.

Electroactive polymers (EAPs) generate highly non-linear deflections when they are used as actuators, which are known as artificial muscles. Though several modelling methods have been proposed before to understand their mechanical, chemical, electrical behaviours or 'electro-chemo-mechanical' behaviour, estimating the whole shape deflection of the EAP actuators has not been studied yet. Therefore, we report on (i) an effective methodology to estimate these actuators' whole shape deflection by employing a soft robotic actuator/manipulator approach and (ii) an angle optimization method, which we call AngleOPT, to accurately solve the EAP actuators' inverse kinematic problem. Laminated polypyrrole (PPy) EAP actuators are employed to validate the soft robotic kinematic model which has more degrees of freedom than its input. This follows that we have reduced a difficult problem to an easy-to solve inverse kinematic problem (easier to solve) of a hyper-redundant soft robotic system. A parametric estimation model is also proposed to predict the tip coordinates of the actuators for a given voltage. The experimental and numerical results are presented to demonstrate the efficacy of the methodology for estimating the EAP actuators' highly non-linear bending behaviour from the inverse kinematic model. The proposed methodology can be extended to other type of smart structures with a similar topology. © 2013 Elsevier Ltd.

Biologically inspired robotic applications have recently received significant attention due to developments in novel materials and actuators with an operation principle similar to the natural muscles’. Electroactive polymer (EAP) actuators, also known as artificial muscles, possess extraordinary properties such as low efficiency consumption, compliance, bio-compatibility and ability to be miniaturized. Although several methodologies have been proposed for modeling and identification of their quasi-static bending behavior, a negligibly small attention has been given to their dynamic behavior. In this paper, we, therefore, report on their electromechanical modeling and parameter identification. We model the tri-layer EAP actuators as a soft robotic actuator consisting of a significant number of rigid links connected with compliant revolute joints. The experimental and numerical results presented suggest that the soft robotics approach is an effective way to model the EAP actuator and subsequently identify its dynamic parameters accurately. We have previously employed the same soft robotic approach to estimate the whole shape of the EAP actuator as a function of time.

Electroactive polymers (EAPs), also called ‘artificial muscles’, offer a significant potential to articulate soft robotic devices, especially bio-inspired robotic devices, due to their remarkable properties of compliance, low electrical energy consumption, suitability for miniaturization, biocompatibility, ability to operate in aqueous environments as well as in air, and high force output to weight ratio. The EAPs are such special materials that they can be tailored to serve as both sensors and actuators. The EAPs as actuators can be employed as either a soft robotic actuator or a soft robotic manipulator especially in the micro domain for cutting edge applications such as micro manipulation systems, medical devices with higher dexterity, soft catheters with built-in actuation, bio-inspired robotics with better mimicking properties and active compliant mechanisms. To realise these applications, there is an increasing need for enhanced modelling methodologies. The subject of this thesis is, therefore, to establish effective modelling and system identification methodologies to predict the time-varying behaviour of the smart actuators typified by polypyrrole (PPy) trilayer laminated actuators, (i.e. ionic type EAP actuators), and to apply these methodologies to predict the behaviour of new planar and spatial mechanisms articulated with these actuators. This thesis systematically develops a whole structure bending behaviour estimation model based on the differential geometry: the backbone curve approach, which is called the ‘soft robotic model’ of the EAP actuator. Before developing a 3- dimensional (3D) soft robotic kinematic model of the EAP actuator, 2-dimensional (2D) kinematic and dynamic soft robotic models have been derived. 2D soft robotic kinematic and dynamic models have been validated experimentally for a range of electrical stimuli (0.0 − 1.0 V). Following that, image and video processing algorithms are employed to obtain the tip position data of the PPy-EAP

Electroactive polymer (EAP) actuators have been attracting the attention of researchers due to their muscle-like behaviour and unusual properties. Several modelling methods have been proposed to understand their mechanical, chemical, electrical behaviours or ‘electro-chemo-mechanical’ behaviour. However, estimating the whole shape or configuration of the EAP actuators has always been challenging due to their highly non-linear bending behaviour. This paper reports on an effective method to estimate the whole shape deflection of the EAP actuators by employing a so-called backbone approach. Tri-layer configured polypyrrole (PPy) based EAP actuators were used as a soft and smart structure with more degrees of freedom than its input. After deriving the inverse kinematic model of the actuator, its complete shape is estimated by solving the inverse kinematic model with an angle optimization (AngleOPT) method. The experimental results and numerical results have demonstrated the effectiveness of the method in estimating the highly non-linear bending behaviour of the PPy actuators and applicability of this modelling approach to other EAP actuators.

Conventional robotic manipulators have been widely studied and proven for their efficiency in macro environment. However, it is unlikely to miniaturize them to mimic a bacterium flagellum type actuator/manipulator. Electroactive polymer (EAP) actuators, also known as artificial muscles, can operate both in wet and dry environments and are very suitable for miniaturising. With this in mind, this paper reports on the kinematics of an artificial flagellum of a bacterium engineered from an EAP actuator. A kinematic model based on backbone curve approach which integrates differential geometry and Denavit-Hartenberg formulation is developed. Simulation results of the artificial flagellum demonstrate the feasibility of such modelling approach for highly flexible EAP actuators. Also, preliminary experiments were conducted. This study recommends that electroactive polymer actuators can be used to build bacteria flagellum type actuators to be used in micro robots for medical purposes such as diagnosis and drug delivery.

In this paper, we report on a multistable linear actuation mechanism articulated with electroactive polymer actuators, widely known as artificial muscles. These actuators, which can operate both in wet and dry media under as small as 1.0 V potential difference, are fundamentally cantilever beams made of two electroactive polymer layers (polypyrrole) and a passive polyvinylidene fluoride substrate in between the electroactive layers. The mechanism considered is kinematically analogous to a four-bar mechanism with revolute-prismatic-revolute-prismatic pairs, converting the bending displacement of a polymer actuator into a rectilinear movement of an output point. The topology of the mechanism resembles that of bistable mechanisms operating under the buckling effect. However, the mechanism proposed in this paper can have many stable positions depending on the input voltage. After demonstrating the feasibility of the actuation concept using kinematic and finite element analyses of the mechanism, experiments were conducted on a real mechanism articulated with a multiple number (2, 4, or 8) of electroactive polymer actuators, which had dimensions of 12×2×0.17 mm3. The numerical and experimental results demonstrate that the angular displacement of the artificial muscles is accurately transformed into a rectilinear motion by the proposed mechanism. The higher the input voltage, the larger the rectilinear displacement. This study suggests that this multistable linear actuation mechanism can be used as a programmable switch and/or a pump in microelectromechanical systems (MEMS) by adjusting the input voltage and scaling down the mechanism further.

Electroactive polymer actuators, also known as artificial muscles, can operate both in wet and dry media under as small as 1 Volt potential difference. This paper reports on a multi-stable linear actuation mechanism articulated with artificial muscles. Kinematic and finite element analyses of the mechanism are studied to demonstrate the feasibility of the mechanism. Experiments were conducted on a real mechanism articulated with a multiple number (4 or 8) of electroactive polymer actuators, which had the dimensions of 12×2×0.17mm. The numerical and experimental results demonstrate that the angular displacement of the artificial muscles is accurately transformed into a rectilinear motion by the proposed mechanism. This study suggests that this multi-stable linear actuation mechanism can be used as a programmable switch and/or a pump in MEMS by adjusting the input voltage and scaling down the mechanism further.

Electroactive conducting polymer actuators have been proposed as alternative to conventional actuators due to their extraordinary properties. This paper reports on a stiffness enhancement methodology for cantilever type conducting polymer actuators based on a suitably designed contact surface with which the actuators are in contact during operation. Finite element analysis and modeling are used to quantify the effect of the contact surface on the effective stiffness of a tri-layer cantilevered beam, which represents one-end free, the other end fixed polypyrrole (PPy) conducting polymer actuator under a uniformly distributed load. After demonstrating the feasibility of the stiffness enhancement concept, experiments were conducted to determine the stiffness of bending-type conducting polymer actuators in contact with a range (20-40 mm in radius) of circular contact surfaces. The simulation and experimental results demonstrate that the stiffness of the actuators can be varied in a nonlinear fashion using a suitably profiled contact surface. The larger is the radius of the contact surface, the higher is the stiffness of the polymer actuators.

This paper reports on a stiffness enhancement methodology based on using a suitably designed contact surface with which cantilevered-type conducting polymer bending actuators are in contact during operation. The contact surface constrains the bending behaviour of the actuators. Depending on the topology of the contact surface, the resistance of the polymer actuators to deformation, i.e. stiffness, is varied. As opposed to their predecessors, these polymer actuators operate in air. Finite element analysis and modelling are used to quantify the effect of the contact surface on the effective stiffness of a trilayer cantilevered beam, which represents a one-end-free, the-other-end-fixed polypyrrole (PPy) conducting polymer actuator under a uniformly distributed load. After demonstrating the feasibility of the adjustable stiffness concept, experiments were conducted to determine the stiffness of bending-type conducting polymer actuators in contact with a range (20–40 mm in radius) of circular contact surfaces. The numerical and experimental results presented demonstrate that the stiffness of the actuators can be varied using a suitably profiled contact surface. The larger the radius of the contact surface is, the higher is the stiffness of the polymer actuators. The outcomes of this study suggest that, although the stiffness of the artificial muscles considered in this study is constant for a given geometric size, and electrical and chemical operation conditions, it can be changed in a nonlinear fashion to suit the stiffness requirement of a considered application. The stiffness enhancement methodology can be extended to other ionic-type conducting polymer actuators.

Synthesis methods used to produce poly(2-methoxyaniline-5-sulfonic acid) (PMAS), a water-soluble, self-doped conducting polymer, have been shown to form two distinctly different polymer fractions with molecular weights of approximately 2 kDa and 8-10 kDa. The low molecular weight (LMWT) PMAS fraction is redox inactive and nonconducting, while the high molecular weight (HMWT) PMAS is electro-active with electrical conductivities of 0.94 +/- 0.05 S cm(-1). Previous investigations have illustrated the different photochemical and electrochemical properties of these fractions but have not correlated these properties with the structural and electronic interactions that drive them. Incomplete purification of the PMAS mixture, typically via bag dialysis, has been shown to result in a mixture of approximately 50:50 HMWT:LMWT PMAS with electrical conductivity significantly lower at approximately 0.10-0.26 S cm(-1). The difference between the electrical conductivities of these fractions has been investigated by the controlled addition of the nonconducting LMWT PMAS fraction into the HMWT PMAS composite film with the subsequent electronic properties investigated by solid-state ESR and Raman spectroscopies. These studies illustrate strong electronic intereactions of the insulating LMWT PMAS with the emeraldine salt HMWT PMAS to substantially alter the population of the electronic charge carriers in the conducting polymer. ESR studies on these mixtures, when compared to HMWT PMAS, exhibited a lower level of electron spin in the presence of LMWT PMAS indicative of the formation of low spin bipolarons without a change in the oxidation state of the conducting HMWT fraction.