Refined Modeling for Serial Pneumatic Artificial Muscles Enables Model-Based Actuation Design

Development of soft actuators often considers the actuator as a unit with a single force and positional output, but the compliance of soft actuators means this is a narrow view of the design space. Recent work has begun to extended single actuator design to produce set trajectories or movements, though often as design of integrated systems. In this work, we propose an actuator design space in this direction, a generalization of serial pneumatic artificial muscles (sPAMs) which allows variable actuation along the length of a compliant backbone. This result is enabled by an evolution of the classical Pleated Pneumatic Artificial Muscle (PPAM) model, expanding the range of actuator geometries for which the force-strain behavior can be predicted. As such, muscle units which are partially inactive or asymmetrically constrained can be predicted and combined in a single serial PAM. Our model enables an extended design space for serial PAMs, which is applied to actuating an inflated beam structure to achieve pre-programmed compound curvatures.