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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Unfolding Textile-Based Pneumatic Actuators for Wearable Applications
Textile based pneumatic actuators have recently seen increased development for use in wearable applications thanks to their high strength to weight ratio and range of achievable actuation modalities. However, the design of these textile-based actuators is typically an iterative process due to the complexity of predicting the soft and compliant behavior of the textiles. In this work we investigate the actuation mechanics of a range of physical prototypes of unfolding textile-based actuators to understand and develop an intuition for how the geometric parameters of the actuator affect the moment it generates, enabling more deterministic designs in the future. Under benchtop conditions the actuators were characterized at a range of actuator angles and pressures (0 – 136 kPa), and three distinct performance regimes were observed, which we define as Shearing, Creasing, and Flattening. During Flattening, the effects of both the length and radius of the actuator dominate with maximum moments in excess of 80 Nm being generated, while during Creasing the radius dominates with generated moments scaling with the cube of the radius. Low stiffness spring like behavior is observed in the Shearing regime, which occurs as the actuator approaches its unfolded angle. A piecewise analytical model was also developed and compared to the experimental results within each regime. Finally, a prototype actuator was also integrated into a shoulder assisting wearable robot, and on-body characterization of this robot was performed on five healthy individuals to observe the behavior of the actuators in a wearable application. Results from this characterization highlight that these actuators can generate useful on-body moments (10.74 Nm at 90° actuator angle) but that there are significant reductions compared to bench-top performance, in particular when mostly folded and at higher pressures.
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- Award ID(s):
- 2011754
- PAR ID:
- 10499807
- Publisher / Repository:
- Mary Ann Liebert Publishers
- Date Published:
- Journal Name:
- Soft Robotics
- Volume:
- 9
- Issue:
- 1
- ISSN:
- 2169-5172
- Page Range / eLocation ID:
- 163 to 172
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1089/soro.2020.0064
