The Impact of Amplification on Efficiency and Energy Density of Induced Strain Actuators

Abstract To some degree, stroke amplification of solid-state electroceramic driven actuators is necessary in all engineering applications. Accompanying stroke amplification, however, are the penalties of loss of output displacement and loss of energy delivered to the load per unit actuator weight. The penalties can be significant when the actuator is used to drive an external stiffness-type load. Using a model which describes a very commonly used lever-type amplification mechanism, the impact of the stiffness and the attendant weight of various members in the amplification mechanism on energy transfer and energy density of the actuator material (under static conditions) is discussed. The significant finding of the study is that on average, after amplification, the energy density of the actuator is about 20 to 35% of the inherent energy density of the active material alone. In other words, only 20 to 35% percent of the energy density that can be delivered by the electroceramic alone when directly driving an external spring load, is available when the active material is used in a displacement amplified actuator device such as the type depicted in the study. The study also demonstrates that the highest stiffness of the amplification members is not desirable, as it significantly increases weight and thereby reduces the energy density. An active material stiffness to amplification structure stiffness ratio of 0.2 to 0.3 provides the highest overall energy density. The impact of using a variety of materials in the amplification mechanisms, is presented. In addition, the advantage of using high stiffness-to-weight composites and other novel materials is also presented.