S-Drives: A piezo-electric muscle geometry

N. Jones, J. Clark
Auburn University,
United States

Keywords: piezoelectric, actuator, muscle, composable

Summary:

We present a geometry for amplifying piezoelectric strain, suitable for macro and micro applications. Our proposed geometry, in Figure 1, is entirely planar and can potentially be made of polymers, reducing both process price and complexity for mass production. Due to the structure's symmetric deformation, several actuators can be chained together to form much longer actuators. The piezoelectric nature of these actuators gives them high frequency response, power density, and efficiency making them a viable choice for a variety of applications. Specifically, these actuators can be designed for various strain and force combinations, which when combined with their potentially great length, on the order of meters, makes them an extremely flexible entry into the field of artificial muscles. Artificial muscles are highly sought after for many applications, with the most popular approaches being thermally actuated macro-molecules, electroactive polymers, and pneumatics. Each of these have downsides, pneumatic requiring bulky control equipment[1], thermally actuated experiencing saturation and hysteresis, and both electroactive polymers and thermally actuated muscles suffering from mono-directional actuation. Piezoelectric muscles address these issues by requiring simple electronics[2,3,4], and support virtually identical powered contraction and expansion. Hysteresis for piezoelectrics is matter of capacitance, and thus can be reduced by increasing drive current. Ultimately, piezoelectric muscles make up for their reduced performance by allowing for greater flexibility in usage due to their reduced external system costs and their inherent bi-directional powered actuation. Previous piezoelectric structures lack of chainable strain amplification limited them to small scales, or to requiring bulky external strain amplification[5,6]. By moving the strain amplification into the micro scale and amplifying in such a way that allows for chained operation this new structure is capable of scales and performance previously impossible. In this paper, we cover our mathematical model governing this structure and we also compare the simulated strength of these muscles to a range of alternatives, both artificial and natural. Additionally there is a brief a discussion of a range of possible manufacturing techniques.