In the early 1990's several government agencies approached SRI International (formerly Stanford Research Institute) in Menlo Park, California, to address the inefficiency issues of conventional electro-magnetic actuators that are commonly used for robotic and many other applications. These agencies commissioned research and development of a new generation of actuation technology. This work led to the development of Electroactive Polymer Artificial Muscle (EPAM™) which is now being commercialized exclusively by Artificial Muscle Inc. (AMI).
How Does EPAM Work?
EPAM consists of a thin layer of dielectric polymer film between two conductive, compliant electrodes. When a voltage potential is applied across the electrodes, the Maxwellian pressure of the positive charge attracting the negative charge causes the electrodes to attract each other, and since the film is elastomeric and incompressible, the film contracts in thickness and expands in area. This basic operation can be seen below. The technology is essentially an elastomeric capacitor that is capable of changing capacitance by applying a voltage or by an external mechanical force. EPAM film is turned into an actuator by attaching frames or materials that direct the motion into the desired axes.
Basic construction of a EPAM device (a) power supply and electronics (b) top electrode layer (c) dielectric elastomer film (d) bottom electrode layer Top: Voltage off Bottom: Voltage on
EPAM achieves significant motion (strain) from this electrostatic pressure as compared to other technologies. The overall displacement is a function of the area of EPAM, and the force exerted is a function of the number of layers of EPAM. Furthermore, the electrode layer of the EPAM can be patterned to achieve specific regions and directions of motion. This EPAM architecture along with configurations, applications, and fabrication processes were developed and patented by SRI International and are now licensed exclusively to Artificial Muscle, Inc.
How can EPAM be used?
EPAM layers can be constructed in multiple configurations. The configurations that AMI is currently offering for haptic feedback and other applications are X-Mode, Diaphragm, and Z-Mode. The X-Mode configuration provides push and pull in-plane motion with a very thin profile that is preferred for many haptic feedback applications. The Diaphragm configuration, originally developed for pumps and valves, provides push and pull out-of-plane motion in a compact design that can be versatile for many applications thus called the Universal Muscle Actuator (UMA). The Z-Mode configuration provides a contraction in the thickness direction, z-axis, that is useful for touch screen haptics for a variety of sized screens.
