Designing components using SmartMOVETM electroactive polymer technology requires an understanding of the basic
operation principles and the necessary design tools for integration into actuator, sensor and energy generation
applications. Artificial Muscle, Inc. is collaborating with OEMs to develop customized solutions for their applications
using smartMOVE. SmartMOVE is an advanced and elegant way to obtain almost any kind of movement using
dielectric elastomer electroactive polymers. Integration of this technology offers the unique capability to create highly
precise and customized motion for devices and systems that require actuation. Applications of SmartMOVE include
linear actuators for medical, consumer and industrial applications, such as pumps, valves, optical or haptic devices. This
paper will present design guidelines for selecting a smartMOVE actuator design to match the stroke, force, power, size,
speed, environmental and reliability requirements for a range of applications. Power supply and controller design and
selection will also be introduced. An overview of some of the most versatile configuration options will be presented
with performance comparisons. A case example will include the selection, optimization, and performance overview of a
smartMOVE actuator for the cell phone camera auto-focus and proportional valve applications.
While Electroactive Polymer Artificial Muscle (EPAM) has been presented extensively as a solution for actuation and generation technology, EPAM technology can also be used in multiple novel applications as a discrete or integrated sensor. When an EPAM device, an elastic polymer with compliant electrodes, is mechanically deformed, both the capacitance of the EPAM device, as well as the electrode and dielectric resistance, is changed. The capacitance and resistance of the sensor can be measured using various types of circuitry, some of which are presented in this paper. EPAM sensors offer several potential advantages over traditional sensors including operation over large strain ranges, ease of patterning for distinctive sensing capabilities, flexibility to allow unique integration into components, stable performance over a wide temperature range and low power consumption. Some existing challenges facing the commercialization of EPAM sensors are presented, along with solutions describing how those challenges are likely to be overcome. The paper describes several applications for EPAM sensors, such as an integrated diagnostic tool for industrial equipment and sensors for process and systems monitoring.
Electroactive Polymer Artificial Muscle (EPAM[R]) technology is becoming a robust, high performance, cost effective solution for commercial applications in many sectors. Since its inception in 2004, Artificial Muscle, Inc. (AMI), a spinout company from SRI International, has rigorously pursued the commercialization of this form of artificial muscle technology through innovative designs and fabrication processes, dramatically increasing performance, reliability and manufacturability across a wide variety of applications. Scaleable solutions developed by AMI include air and liquid pumps, valves, linear and angular positioners, rotary motors, sensors and generators. Innovative device designs demonstrating the ability to meet the specifications of demanding applications across broad operating environments and combining practical levels of power densities and actuation lifetimes will be discussed. Integrated electronics control modules allow the freedom to design artificial muscles directly into new or existing product lines while effectively managing the transition from conventional technologies. Simple modular, versatile designs, coupled with low cost industrial materials and flexible automated manufacturing processes, provide a cost effective solution for products serving such diverse industries as consumer electronics, medical devices, and automobiles. Several case examples are presented to illustrate the commercial viability of EPAM[R]-based devices.
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.
Dielectric elastomer artificial muscles (electroelastomers) have
been shown to exhibit excellent performance in a variety of actuator configurations. By rolling highly prestrained electroelastomer films onto a central compression spring, we have demonstrated multifunctional electroelastomer rolls (MERs) that combine load bearing, actuation, and sensing functions. The rolls are compact, have a potentially high electroelastomer-to-structure weight ratio, and can be configured to actuate in several ways including axial extension and bending, and as multiple degree-of-freedom (DOF)
actuators that combine both extension and bending. 1-DOF, 2-DOF, and 3-DOF MERs have all been demonstrated through suitable electrode patterning on a single monolithic substrate. The bending MER actuators can act as leg and knee joints to produce biomimetic walking that is adaptable to many environments. Results of animation and the fabrications of a robot model of a synthetic bug or animal based on the MERs are presented. A new concept for an antagonist actuator for more precise control is introduced.
To achieve desirable biomimetic motion, actuators must be able to reproduce the important features of natural muscle such as power, stress, strain, speed of response, efficiency, and controllability. It is a mistake, however, to consider muscle as only an energy output device. Muscle is multifunctional. In locomotion, muscle often acts as an energy absorber, variable-stiffness suspension element, or position sensor, for example. Electroactive polymer technologies based on the electric-field-induced deformation of polymer dielectrics with compliant electrodes are particularly promising because they have demonstrated high strains and energy densities. Testing with experimental biological techniques and apparatus has confirmed that these dielectric elastomer artificial muscles can indeed reproduce several of the important characteristics of natural muscle. Several different artificial muscle actuator configurations have been tested, including flat actuators and tubular rolls. Rolls have been shown to act as structural elements and to incorporate position sensing. Biomimetic robot applications have been explored that exploit the muscle-like capabilities of the dielectric elastomer actuators, including serpentine manipulators, insect-like flapping-wing mechanisms, and insect-like walking robots.