Search

We report a flexible visuo-haptic display that allows for interactive haptic feedback on the visual display. The visuo-haptic display is fabricated by integrating a dielectric elastomer (DE) based thin film actuator array into a flexible display and pressure sensors. The DE actuator array consists of nine active cells, which generate thickness-mode deformation in response to voltage signal. The flexible display presents images of the aligned three alphabet characters at each section in 3 × 3 matrix during light propagation via optical multiwaveguide. The pressure sensors are placed on the bottom of the DE actuator array for haptic feedback. The performance of the DE actuators is proved to be capable of realizing sufficient vibro-tactile sensation in the perceivable range of human touch sense. The integrated system enables the visual display to provide interactive haptic feedback such as key pressing, contact vibration sensations, etc., in accordance with user input.

This paper describes a flexible visuo-haptic display module. We have developed a flexible electro-active polymer (EAP) actuator and a thin flexible visual display with array configuration via polymer technology. The flexible actuator consists of nine EAP cells vertically moving in response to change in their thickness. The flexible display uses polymer based optical waveguide allowing light to scatter only at specific area. The display film is transparent and identically designed to the array pattern to fit for the arrangement of actuator cells. A pressure sensor is installed under the integrated module. The performance of the actuator is proved to be sufficient for satisfying perceivable range of human touch sense. The integrated system can provide interactive haptic feedback such as key pressing, contact vibration sensations, and etc. in accordance with user input.

Stretchable electronics can go beyond what might commonly be considered “electronics.” They can exploit their inherent elasticity to enable new types of transducers that convert between electrical energy and mechanical energy. Dielectric elastomer actuators are “stretchable capacitors” that can offer muscle-like strain and force response to an applied voltage. As generators, dielectric elastomers offer the promise of energy harvesting with few moving parts. Power can be produced simply by stretching and contracting a relatively low-cost rubbery material. This simplicity, combined with demonstrated high energy density and high efficiency, suggests that dielectric elastomers are promising for a wide range of energy-harvesting applications. Indeed, dielectric elastomers have been demonstrated to harvest energy from human walking, ocean waves, flowing water, blowing wind, pushing buttons, and heat engines. While the technology is promising and advances are being made, there are challenges that must be addressed if dielectric elastomers are to be a successful and economically viable energy-harvesting technology. These challenges include developing materials and packaging that sustain a long lifetime over a range of environmental conditions, designing the devices that stretch the elastomer material uniformly, and system issues such as practical and efficient energy-harvesting circuits.

This article presents the material modeling and experimental characterization of SMA rod and tube actuators undergoing pure torsional deformations. The investigation of the torsional characteristics of SMAs is carried out in order to gain a fundamental understanding of the behavior of SMA torsional actuators. The proposed application is to alter the twist distribution of a tiltrotor blade from hover to forward flight modes, providing improved flight efficiency in both modes of flight. To describe the behavior of the actuator, a torsional model involving the extension of the one-dimensional (uniaxial) formulation of SMA phenomenology is presented. As an example, Brinson's model is chosen as the representative uniaxial model; however, the approach used here to extend the uniaxial model into the torsional domain is applicable to nearly any uniaxial SMA model. The parameters for the uniaxial model are derived from extensional testing of an SMA rod or tube, and are then used to predict the torsional characteristics of the same material. A major advantage of this method compared to prior art in torsional modeling is that the simplicity of deriving and implementing the parameters from uniaxial testing is carried over into the torsional domain. This simplicity derives from the fact that the measured properties (forces and displacements) in tensile loading are more readily suited to determining the model parameters than the measured properties in torsional loading which have been used by previous researchers (angles and torques which are, in fact, integrated quantities from strains and stresses). This article also presents a comprehensive experimental investigation and model correlation with both tension and torsional behavior of SMA rods and tubes. The model is compared with experimental data including torsional actuation tests against torsional springs. It is shown that the theoretical model demonstrates good agreement with the experimental data over a wide range of thermomechanical conditions. In addition, experimental phenomena associated with the torsional behavior of the SMA actuator such as the effects of heat treatment, twist rate, and loading pattern are examined.

Electroelastomers (electroactive elastomers) such as the 3M VHB 4910 acrylic adhesive films have exhibited up to 380% strain in area expansion at 5?6?kV when they are highly prestrained. By rolling highly prestrained electroelastomer films around a compression spring, we have demonstrated multifunctional electroelastomer rolls (MERs, or spring rolls) that combine load bearing, actuation, and sensing functions. We extended the design to two-degree-of-freedom (2-DOF) and 3-DOF spring rolls by patterning the electrodes to align radially on two and four circumferential spans of the rolls, respectively. Multiple-DOF spring rolls retain the linear actuation of 1-DOF spring rolls with additional bending actuation. Mathematical equations are derived to correlate the bending angle and lateral force of the rolls with the actuated stroke in one of the electroded spans. Two-DOF spring rolls with a 1.4?cm outside diameter, 6.8?cm axial length, and 11?g weight have been fabricated; these rolls have a 90? maximum actuation bending angle, 0.7?N maximum lateral force, and up to 15?N blocked axial force. Three-DOF spring rolls with a 2.3?cm outside diameter, 9.0?cm axial length, and 29?g weight exhibit a 35? maximum bending angle and 1.0?N maximum lateral force. These specifications can be modified by variations in roll parameters according to the equations. Multi-DOF spring rolls are easy to fabricate, compact, multifunctional, and mechanically robust. They represent a radically new actuation technology and may enable a number of unique applications. We have demonstrated a small walking robot, MERbot, with one 2-DOF spring roll as each of its six legs. The robot's speed is as high as 13.6?cm?s?1 or two-thirds of its length per second. 'Sushi rolls' have also been fabricated: these consist of six 2-DOF springs connected in series and monolithic in structure. The sushi rolls can be driven so as to generate wavelike or serpentine motion.

Electroactive polymer transducers have many features that are desirable for MEMS devices. An especially attractive type of electroactive polymer is dielectric elastomer. Dielectric elastomers, transducers that couple the deformation of a rubbery polymer film to an applied electric field, show particular promise with features such as simple fabrication in a variety of size scales, high strain and energy density, high efficiency and fast speed of response, and inherent flexibility, environmental tolerance, and ruggedness. A variety of actuator configurations has been demonstrated at the small size scales needed for MEMS devices, including rolled “artificial muscle" actuators, framed and bending beam actuators for efficient opto-mechanical switches, and diaphragm and thickness mode actuators for pumps and valves. The performance benefits of electroactive polymers can allow for new generations of devices in microrobotics, communications, and biotechnology. Several challenges remain for electroactive polymers, including microfabrication, integration with driving electronics, and operational lifetime.

This paper describes a modeling approach to incorporate the effects of nonquasistatic loading on the extensional behavior of an SMA wire. Experimental results under a variety of loading conditions indicate that the instantaneous temperature of the material is closely related to the applied strainrate in the material. In order to predict this behavior, a coupled thermo-mechanical analysis with the rate form of SMA constitutive models is formulated. The temperatures and temperature rates are not prescribed, but are derived from energy conservation of the material. The stress rate is simultaneously derived using the rate form of SMA constitutive models. Important parameters governing heat transfer such as specific heat, heat transfer and latent heat are modeled and validated with experimental data. For the material tested (0.38 mm diameter SMA wire), the quasistatic strain rate below which no significant deviation in material characteristics are observed was empirically determined to be about 0.0005/s. At a strain rate of 0.01/s, the transformation stresses in the material are increased by approximately 0.5 × 10 8 Pa, accompanied by an increase in temperature of about 2°C over the quasistatic values. The predictions for the stress-strain curves are compared with experimental data at different strain rates over a range of environmental temperatures, and are found to be in good qualitative agreement. The model is also shown to be in good qualitative agreement with the experimental behavior under more complex loading conditions involving two different strain rates of loading. Parametric variation of the model coefficients is discussed. Although the qualitative aspects of the model are in good agreement with experimental data, it is argued that more comprehensive estimation of the model parameters is required to assess the quantitative aspects of the model. The model described in the paper uses the rate forms of the Brinson model. However, it is equally applicable with a modified rate-dependant form of any other quasistatic model describing SMA behavior.

Dielectric elastomer actuators are “stretchable capacitors” that can offer muscle-like strain and force response to an applied voltage. As generators, dielectric elastomers offer the promise of energy harvesting with few moving parts. Power can be produced simply by stretching and contracting a relatively low-cost rubbery material. This simplicity, combined with demonstrated high energy density and high efficiency, suggests that dielectric elastomers are promising for a wide range of energy-harvesting applications. Indeed, dielectric elastomers have been demonstrated to harvest energy from human walking, ocean waves, flowing water, blowing wind, pushing buttons, and heat engines. While the technology is promising and advances are being made, there are challenges that must be addressed if dielectric elastomers are to be a successful and economically viable energy-harvesting technology. These challenges include developing materials and packaging that sustain a long lifetime over a range of environmental conditions, designing the devices that stretch the elastomer material uniformly, and system issues such as practical and efficient energy-harvesting circuits.

Dielectric elastomers offer the promise of energy harvesting with few moving parts. Power can be produced simply by stretching and contracting a relatively low-cost rubbery material. This simplicity, combined with demonstrated high energy density and high efficiency, suggests that dielectric elastomers are promising for a wide range of energy harvesting applications. Indeed, dielectric elastomers have been demonstrated to harvest energy from human walking, ocean waves, flowing water, blowing wind, and pushing buttons. While the technology is promising, there are challenges that must be addressed if dielectric elastomers are to be a successful and economically viable energy harvesting technology. These challenges include developing materials and packaging that sustains long lifetime over a range of environmental conditions, design of the devices that stretch the elastomer material, as well as system issues such as practical and efficient energy harvesting circuits. Progress has been made in many of these areas. We have demonstrated energy harvesting transducers that have operated over 5 million cycles. We have also shown the ability of dielectric elastomer material to survive for months underwater while undergoing voltage cycling. We have shown circuits capable of 78% energy harvesting efficiency. While the possibility of long lifetime has been demonstrated at the watt level, reliably scaling up to the power levels required for providing renewable energy to the power grid or for local use will likely require further development from the material through to the systems level.

Electroactive polymers (EAPs) that are suitable for actuators undergo changes in size, shape, or stress state upon the application of an electrical stimulus. Much research in the field of EAPs tends to focus on the development and understanding of the polymer materials themselves. However, practical devices require that changes in dimension and stress state be effectively exploited to produce the desired functionalities (e.g., driving the motion of a robot limb or simply changing appearance or surface texture). This chapter focuses on those issues that must be considered in implementing EAP materials in practical devices. For purposes of discussion we will focus on one particular type of electroactive polymer: dielectric elastomers. In the literature [e.g., Liu, Bar-Cohen, and Leary, 1999] and elsewhere in this book, dielectric elastomers are also known as electrostatically stricted polymers. Dielectric elastomers are a type of electronic EAPs as defined in Chapter 1 of this book - €”in that their operation is based on the electromechanical response of polymer materials to the application of an electric field. They have demonstrated good performance over a range of performance parameters and thus show potential for a wide range of applications. Dielectric elastomers were pioneered by SRI International, but several research groups around the world are actively investigating applications of this technology [e.g., Wingert et al., 2002; Sommer-Larsen et al., 2001; Jeon et al., 2001]. While the principle of operation of dielectric elastomer EAPs is not used with all EAPs, many of the issues we will discuss are common to all. These issues include the high compliance and large strains that EAPs can produce, as well as the necessity of simultaneous consideration of both the electrical properties and mechanical properties of materials. This chapter is organized as follows. First, we consider the specifications used to match actuation technologies with applications, and when it makes sense to consider EAPs. Next, we discuss the basic principles of dielectric elastomer technology. We then consider design issues that may affect the actuation performance of dielectric elastomer EAPs, as well as the operational characteristics of EAPs and how they may affect an application. We present several examples of dielectric elastomer actuators for a wide range of applications, highlighting both the potential advantages of EAPs and the challenges associated with their use. Finally, we conclude with a brief summary of the subchapter and a discussion of the future of EAP application.

To determine the force requirements, optimal vector, and appropriate materials of a novel eyelid sling device that will be used to rehabilitate eyelid closure (blink) in congenital or acquired permanent facial paralysis with an artificial muscle.The force required to close the eyelids in human cadavers (n = 6) were measured using a load cell system. The eyelid sling using either expanded polytetrafluoroethylene (ePTFE) or temporalis muscle fascia was implanted. The ideal vector of force and placement within the eyelid for a natural eyelid closure were compared.The eyelid sling concept was successful at creating eyelid closure in a cadaver model using an upper eyelid sling attached to the distal tarsal plate. Less force was necessary to create eyelid closure using a temporalis muscle fascia sling (627 +/- 128 mN) than for the ePTFE eyelid sling (1347 +/- 318 mN).The force and stroke required to close an eyelid with the eyelid sling are well within the attainable range of the electroactive polymer artificial muscle (EPAM). This may allow the creation of a realistic and functional eyelid blink that is symmetric and synchronous with the contralateral, normally functioning blink. Future aims include consideration of different sling materials and development of both the EPAM device and an articulation between the EPAM and sling. The biocompatibility and durability studies of EPAM in a gerbil model are under way. The successful application of artificial muscle technology to create an eyelid blink would be the first of many potential applications.

The dielectric elastomer, a particularly attractive type of electroactive polymer, uses commercial polymers such as acrylic and silicone elastomers. The technology has been limited in application by perceived lifetime issues. By addressing several lifetime issues, lifetimes of more than one million cycles, and in some cases beyond ten million cycles, were achieved with a variety of transducer configurations (including operation in generator mode) under a variety of operating conditions (including high humidity). Dielectric elastomers can produce maximum actuation strains of more than 100% and specific energy density exceeding that of known electric-field induced technology. Performance testing for dielectric elastomer actuators has typically been for peak-performance or “over-driven” conditions with short operational lifetimes (typically 100s or 1000s of cycles), particularly under conditions such as high humidity. By minimizing electric field and mechanical strain concentration factors, long lifetimes (>1 million cycles) with acrylic transducers were achieved with actuation strains as great as 40% areal strain (and up to 100% areal strain in generator mode). Actuators in a dry environment had an almost 20x increase in lifetime over actuators at ambient humidity (about 50% RH) at the same driving field conditions. Long actuation lifetimes were also achieved in a 100% RH environment and when fully submerged in salt water at reduced operating strain and field. In 100% RH, lifetimes of several million cycles were achieved at 4% strain. In underwater operation, 6 out of 11 actuators survived for >10 million cycles with an electric field limited to 32 MV/m and approximately 2% strain. The demonstrated lifecycle improvements are applicable to a variety of uses of dielectric elastomers, including haptic interface devices, pumps (implantable and external), optical positioners, and “artificial muscles” to replace small damaged muscles. Continued improvements in materials, actuator design, and packaging, combined with management of operational conditions as described here, should support new practical application of this promising technology.

This paper describes a novel clamping technology called compliant electroadhesion, as well as the first application of this technology to wall climbing robots. As the name implies, electroadhesion is an electrically controllable adhesion technology. It involves inducing electrostatic charges on a wall substrate using a power supply connected to compliant pads situated on the moving robot. High clamping forces (0.2-1.4 Newton supported by 1 square centimeter of clamp area, depending on substrate) have been demonstrated on a wide variety of common building substrates, both rough and smooth as well as both electrically conductive and insulating. Unlike conventional adhesives or dry adhesives, the electroadhesion can be modulated or turned off for mobility or cleaning. The technology uses a very small amount of power (on the order of 20 microwatts/Newton weight held) and shows the ability to repeatably clamp to wall substrates that are heavily covered in dust or other debris. Using this technology, SRI International has demonstrated a variety of wall climbing robots including tracked and legged robots.

Many different actuator configurations based on SRI International’s dielectric elastomer (DE) type of electroactive polymer (EAP) have been developed for a variety of applications. These actuators have shown excellent actuation properties including maximum actuation strains of up to 380% and energy densities of up to 3.4 J/g, using the planar mode of actuation. Recently, SRI has investigated different configurations of DE actuators that allow complex changes in surface shape and thus the creation of active surface texture. In this configuration, the “active” polymer film is bonded or coated with a thicker passive layer, such that changes in the polymer thickness during actuation of the DE device are at least partially transferred to (and often amplified by) the passive layer. Although the device gives out-of-plane motion, it can nonetheless be fabricated using two-dimensional patterning. The result is a rugged, flexible, and conformal skin that can be spatially actuated by subjecting patterned electrodes on a polymer substrate to an electric field. Using thickness-mode DE, we have demonstrated thickness changes of the order of 0.5 - 2 mm by laminating a passive elastomeric layer to a DE polymer that is only 60 μm in thickness. Such thickness changes would otherwise require a very large number of stacked layers of the DE film to produce comparable surface deformations. Preliminary pressures of 4.2 kPa (0.6 psi) in a direction normal to the plane of the DE film have been measured. However, theoretical calculations indicate that pressures of the order of 100 kPa are feasible using a single layer of DE film. Stacking multiple layers of DE film can lead to a further increase in achievable actuation pressures. Even with current levels of thickness change and actuation pressures, potential applications of such surface texture change are numerous. A thin, compliant pad made from these actuators can have a massaging or sensory augmentation function, and can be incorporated into garments if desired. The bumps and troughs could act as valves or pumping elements in a fluidic or microfluidic system. Such a device could also be the basis of a smart skin that controls boundary-layer flow properties in a boat or airplane so as to reduce overall drag. The DE elements of the pad can also be used as sensors to make a touch-sensitive skin for recording human interaction with the environment. By driving a thin, compliant vibrating layer at resonant frequencies, one can also configure these devices as solid or fluidic conveyors that transport material on a macroscopic or microscopic scale.

Composite materials have increased the range of mechanical properties available to the design engineer compared with the range afforded by single component materials, leading to a revolution in capabilities. Nearly all commonly used engineering materials, including these composite materials, however, have a great limitation; that is, once their mechanical properties are set they cannot be changed. Imagine a material that could, under electric control, change from rubbery to rigid. Such composite "meta-materials" with stiffness and damping properties that can be electrically controlled over a wide range would find widespread application in areas such as morphing structures, tunable and conformable devices for human interaction, and greatly improved vibration control. Such a technology is a breakthrough capability because it fundamentally changes the paradigm of composite materials having a fixed set of mechanical properties. These electronically controllable composites may be the basis of discrete devices with tunable impedance. The composites can also be multifunctional materials: They can minimize size and mass by acting not only as a tunable impedance device, but also as a supporting structure or protective skin. Current approaches to controllable mechanical properties include composites with materials that have intrinsically variable properties such as shape memory alloys or polymers, or magnetorheological fluids, or composites that have active materials such as piezoelectrics, magnetostrictives, and newly emerging electroactive polymers. Each of these materials is suitable for some applications, but no single technology is capable of fast and efficient response that can produce a very wide range of stiffness and damping with a high elongation capability, that is, go from rubber to rigid. Such a material would be capable of a change in its maximum elastic energy of deformation of 50,000 J/cm3. No existing material is within three orders of magnitude of this value. Similarly, no material appears capable of going from a very lightly damped to a very heavily damped condition over a wide range of motion. We suggest an approach based on composites whose meso-scale structure can be changed with actuation or change in intrinsic properties. Passive composite meta-materials have been demonstrated, however, such active composite meta-materials have not yet been demonstrated.

Electroelastomers (electroactive elastomers, a.k.a. dielectric elastomers) such as those based on acrylic elastomer films with compliant electrodes, when highly prestrained, exhibited up to 380% electromechanical strain in area expansion at 5 to 6 kV. By rolling highly prestrained acrylic films around a compression spring, multifunctional electroelastomer rolls (MERs, or spring rolls) were obtained that combined load bearing, actuation, and sensing functions. The design was extended to two-degree-of-freedom (2-DOF) and 3-DOF spring rolls by patterning the electrodes along the circumferential spans of the rolls. Multiple-DOF spring rolls retained the linear actuation of 1-DOF spring rolls with additional bending actuation. New electroelastomers were developed that preserved the high strain and energy capability of the acrylic films but could respond one order of magnitude faster. One-DOF spring rolls using this new material exhibited response speeds up to 100 Hz, and power densities as high as 400 W/kg of actuator mass and 2000 W/kg of electroelastomer mass based on maximum force, stroke, and frequency. Further, new electroelastomers were prepared that exhibited 200% strain without the need for prestrain. These materials may enable new actuators containing no prestrain-supporting structures that are even lighter, more compact, and compliant. The new actuators would have a higher percentage of active mass and higher energy and power densities than those based on the prestrained acrylic films matching the characteristics of animals. A roll actuator containing no supporting structure was fabricated to output 33% strain. Preliminary lifetime measurements confirmed the potentially long lifetime of the electroelastomers. Improvements in MER design and materials have enabled a new generation of small walking robots, MERbot, with a multi-DOF spring roll as each of its six legs, as well as a new type of robot that can be quickly fabricated from a single flat multifunctional actuator structure. Such small flat robots can hop or jump two to three times their height and have been able to quickly clear obstacles equal to the robots' height.

Electroactive polymer (EAP) transducers are an emerging technology with many features that are desirable for MEMS devices. These advantages include simple fabrication in a variety of size scales, and ruggedness due to their inherent flexibility. Dielectric elastomer, a type of EAP transducer that couples the deformation of a rubbery polymer film to an applied electric field, shows particular promise because it can produce high strain and energy density, high efficiency and fast speed of response, and inherent environmental tolerance. A variety of proof-of-principle dielectric elastomer actuator configurations have been demonstrated at the small size scales needed for MEMS devices, including rolled "artificial muscle" actuators for insect-inspired microrobots, framed and bending beam actuators for efficient opto-mechanical switches, diaphragm and enhanced-thickness-mode actuators for microfluidic pumps, and valves and arrays of diaphragms for haptic displays. Several challenges remain for EAPs, including integration with driving electronics, and operational lifetime.

Dielectric elastomer actuators offer unprecedented opportunities for actuation in a wide range of applications. To make appealing large scale and efficient systems, new electronic devices combining high voltage and flexibility need to be designed. In this paper we report the first mechatronic system, made of an array of electro-active polymer based actuators integrated with thin film photoconductive high voltage switches fabricated on a plastic film substrate. The actuator is an acrylic elastomer diaphragm that expands under electrical stimulation. Each actuator is connected to the high voltage power supply through a photoconductive switch, which is addressed and closed by illumination. The amorphous silicon switches are made on flexible and transparent polyimide (Kapton E®) substrates. Individual switches were tested up to 8 kV and a nine-element array was successfully working at 5 kV.

Space-based astronomy and remote sensing systems would benefit from extremely large aperture mirrors that can permit greater-resolution images. To be cost effective and practical, such optical systems must be lightweight and capable of deployment from highly compacted stowed configurations. Such gossamer mirror structures are likely to be very flexible and therefore present challenges in achieving and maintaining the required optically precise shape. Active control based on dielectric elastomers was evaluated in order to address these challenges. Dielectric elastomers offer potential advantages over other candidate actuation technologies including high elastic strain, low power dissipation, tolerance of the space environment, and ease of commercial fabrication into large sheets. The basic functional element of dielectric elastomer actuation is a thin polymer film coated on both sides by a compliant electrode material. When voltage is applied between electrodes, a compressive force squeezes the film, causing it to expand in area. We have explored both material survivability issues and candidate designs of adaptive structures that incorporate dielectric elastomer actuation. Experimental testing has shown the operation of silicone-based actuator layers over a temperature range of -100 °C to 260 °C, suitable for most earth orbits. Analytical (finite element) and experimental methods suggested that dielectric elastomers can produce the necessary shape change when laminated to the back of a flexible mirror or incorporated into an inflatable mirror. Interferometric measurements verified the ability to effect controllable shape changes less than the wavelength of light. In an alternative design, discrete polymer actuators were shown to be able to control the position of a rigid mirror segment with a sensitivity of 1800 nm/V, suggesting that sub-wavelength position control is feasible. While initial results are promising, numerous technical challenges remain to be addressed, including the development of shape control algorithms, the fabrication of optically smooth reflective coatings, consideration of dynamic effects such as vibration, methods of addressing large-numbers of active areas, and stowability and deployment schemes.

This paper presents the material modeling and experimental characterization of SMA rod and tube actuators undergoing torsional deformations. The investigation of the torsional characteristics of SMAs was carried out in order to gain fundamental understanding of the behavior of torsional actuators for actively altering the twist distribution of a tiltrotor blade between hover and forward flight. A torsional model involving the extension of the one-dimensional formulation of Brinson’s model for prediction of SMA behavior is presented. The model is shown to have good correlation with experiment over a wide range of thermomechanical conditions including constant temperature torque-angle and actuation tests against torsional springs. Experimental phenomena associated with the torsional behavior of the SMA actuator such as the effects of heat treatment, twist rate and loading pattern are examined, and limitations of the current model pointed out. It is shown that the theoretical model demonstrates good agreement with the experimental data over a wide thermo-mechanical range of conditions.

This paper presents research aimed at actively altering the twist distribution of a tiltrotor blade between hover and forward flight. Three different concepts-extension-twist coupled composites, bimoment actuation and discrete SMA torque tube actuation - are considered, and the torque tube appears the most feasible. Parametric design of the torque tube and attachment technique is presented with actuation torque, heat transfer and bandwidth issues being considered to arrive at the configuration of the tube. The effect of heat treatment of the SMA in tuning the actuation characteristics is discussed. A dramatic improvement in the actuation cooling time is demonstrated through the use of active cooling using thermodelectric modules. An extension of the one-dimensional formulation of Brinson's model to the torsional case is presented. The model is shown to have good correlation with room temperature characteristics. The criterion for impedance matching between the actuator and the host structure is derived. The torsional actuator is tested both under no load and acting against a restoring spring and shows repeatable actuation characteristics.

Shape memory alloys (SMAs) have shown promise as high-force, high displacement actuators. Critical issues such as path- dependence, predictability and sensitivity to testing conditions, however, need to be addressed in order to design controllable actuators using SMAs. This paper presents research aimed at addressing some of design issues involving application of SMAs, particularly at actuators. Quasistatic experiments at constant stress, strain and temperature are consolidated on a critical stress-temperature diagram to delineate the regions of stability of the various phases of the material. The critical points from these quasistatic tests are found to be in excellent agreement with each other, and correlate relatively well with the constitutive models for SMA thermomechanical behavior. It is also observed that the state of the material is not unique at points along the transformation, and is dependent on the history of the material before the start of the test, individual test involved, the method of loading, and loading rates. Significant variation of the state of the material with different rates and conditions of loading are shown to further illustrate this point. This behavior is likely to be decisive in determining the dynamic behavior of the material, and underscores the need for approaches incorporating these issues for design of repeatable actuators.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Background Current management of permanent facial paralysis centers on nerve grafting and muscle transfer; however, limitations of those procedures call for other options. Objectives To determine the durability and biocompatibility of implanted artificial muscle in a gerbil model and the degree of inflammation and fibrosis at the host tissue–artificial muscle interface. Methods Electroactive polymer artificial muscle (EPAM) devices engineered in medical-grade silicone were implanted subcutaneously in 13 gerbils. The implanted units were stimulated with 1 kV at 1 Hz, 24 h/d via a function generator. Electrical signal input/output was recorded up to 40 days after implantation. The animals were euthanized between 23 and 65 days after implantation, and the host tissue–implant interface was evaluated histologically. Results The animals tolerated implantation of the EPAM devices well, with no perioperative deaths. The muscle devices created motion for a mean of 30.3 days (range, 19-40 days), with a mean of 2.6 × 10 6 cycles (range, 1.6 × 10 6 to 3.5 × 10 6 cycles). Histologic examination of the explanted devices revealed the development of a minimal fibrous capsule surrounding the implants, with no evidence of bacterial infection or inflammatory infiltrate. No evidence of device compromise, corrosion, or silicone breakdown was noted. Conclusions Artificial muscle implanted in this short-term animal model was safe and functional in this preliminary study. We believe that EPAM devices will be a safe and viable option for restoration of facial motions in patients with irreversible facial paralysis.

We demonstrate the first mechatronic device made of an electro-active polymer (EAP) based actuator driven by a thin film photoconductive high voltage switch of amorphous silicon fabricated on a plastic film. The actuator is made of an elastomer dielectric that deforms and expands under high voltage. Its geometry is designed to linearly translate a lightweight rectangular block by the electrostatic expansion of the elastomer. The power supply is connected to the EAP through a photoconductor switch which is addressed and closed by illumination. We describe the configuration of the EAP actuator and the fabrication of the thin film photoconductor, and the electrical parameters and responses of the EAP/photoconductor system.

Dielectric elastomers exhibit remarkable elastic and electroactive properties. Upon kilovolt range electrical stimulation, the polymeric actuator deforms with very large mechanical strain. We made thin film amorphous silicon (a-Si:H) photoconductive switches on 50-μm thick flexible polyimide films to control the polymer actuation. 155–310-nm thick a-Si:H films were grown by plasma enhanced chemical vapor deposition at 150 °C substrate temperature. The photoconductive switches were made with 250-, 500- or 1000-μm gaps formed by electrodes of evaporated aluminum. When properly passivated, the switches have a dielectric breakdown strength of ∼10 kV/mm across the gap. We present optical and electrical characteristics of these a-Si:H switches in the 1–10 kV range. The integration of a nine-element a-Si:H high voltage photoconductor switch array with a nine-element electroactive polymer actuator array is demonstrated. The time constants measured on this array agree well with the values modeled using the a-Si:H photoconductor characteristics.