In this paper, we will investigate the mechanics and performance implications of topological configuration in fluidic artificial muscle tissues. Internal architectural design of biological muscle tissues is known to drive the amount of muscle force produced and the direction in which the muscle tissue moves. Biological muscle tissues exhibit a variety of internal configurations of the muscle fibers relative to muscle axis of motion. The parallel muscle configuration, denoted by muscle fibers arranged parallel to the muscle axis of motion, is known to enable large and fast muscle contractions while observing only moderate muscle force outputs. The pennate muscle configuration, denoted by muscle fibers arranged at an angle from the muscle axis of motion, provides the ability to passively control the architectural gear ratio (AGR) between each fiber contraction and the entire muscle contraction. This variable gearing capacity gives pennate muscles the ability to match force and velocity outputs to specific muscle contraction demands. Furthermore, the larger physiological cross-sectional area of the pennate muscle configuration enables the ability to achieve much greater muscle forces. This is apparent in the behavior and performance of different muscle architectures in the human leg. For example, the pennate muscle configuration in the quad provides the force needed to climb stairs while the parallel muscle configuration in the hamstring enables the muscle contraction needed for running. Thus, natural muscles have inspired many actuators used in robotics, powered prosthetics, and orthoses. Previous studies have established a constitutive force, contraction, and stiffness model for a general pennate muscle configuration actuator, which has been experimentally validated by utilizing McKibben artificial muscles to develop a bio-inspired variable stiffness pennate actuator. A variable stiffness actuator is especially of great interest to roboticists and engineers because of the potential capabilities in energy storage and safety in human-robot interaction. McKibben artificial muscles are suitable for this application due to their high force-to-weight ratio, inherent flexibility, and relatively inexpensive construction properties. This paper expands on previous pennate configuration actuator studies through a comparative investigation on muscle force and variable gearing performance of a pennate muscle configuration actuator against a baseline parallel muscle configuration actuator on an equivalent cross-sectional area. The results allow for justified design decisions on recreating a versatile and adaptive pennate actuator. Future work will include controlling the adaptive stiffness nature of the pennate topology and creating a functioning adaptive actuator capable of altering configuration to meet force, stroke, and stiffness demands.


Comparative Investigation of Pennate vs. Parallel Artificial Muscle Tissue Topologies

Division / Sponsors: 
Aerospace Division

Paper Proceedings: https://asmedigitalcollection.asme.org/SMASIS/SMASIS2020/volume/84027

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