This paper will investigate the effects of pennate angle on fluidic artificial muscle (FAM) bundles for a robot arm motion. Rising interest in soft fluidic actuators exists due to their prospective inherent compliance and safe human-robot interaction. The high force-to-weight ratio, innate flexibility, inexpensive construction, and muscle-like force-contraction behavior of McKibben FAMs make them an attractive type of soft fluidic actuator. Multi-unit architectures found in biological muscles tissues and geometric fiber arrangements have inspired the development of hierarchical actuators to enhance the total actuator performance and increase actuator functionality. Parallel, asymmetric unipennate, and symmetric bipennate are three muscle fiber arrangement types found in human skeletal muscle tissues. Unique characteristics of the pennate muscle tissue, with muscle fibers arranged obliquely from the line of muscle motion, enable passive regulation of effective transmission between the fibers and muscle. Prior studies developed an analytical model based on idealized assumptions to leverage this pennate topology in optimal fiber parameter design for FAM bundles under spatial bounds. The findings showed FAMs in the bipennate topology can be designed to amplify the muscle output force, contraction, and stiffness as compared to that of a parallel topology under equivalent spatial and operating constraints. This work seeks to extend upon previous studies by investigating the effects of pennate angle on actuation and system hydraulic efficiency for a robot arm with a more realistic FAM model. The results will progress toward tailoring actuator topology designs for custom compliant actuation applications.

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