- Award ID(s):
- 1845203
- PAR ID:
- 10322997
- Date Published:
- Journal Name:
- Proceedings of the ASME 2021 Conference on Smart Materials, Adaptive Structures and Intelligent Systems SMASIS 2021
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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In this paper, we investigate the design of pennate topology fluidic artificial muscle bundles under spatial constraints. Soft fluidic actuators are of great interest to roboticists and engineers, due to their potential for inherent compliance and safe human–robot interaction. McKibben fluidic artificial muscles are an especially attractive type of soft fluidic actuator, due to their high force-to-weight ratio, inherent flexibility, inexpensive construction, and muscle-like force-contraction behavior. The examination of natural muscles has shown that those with pennate fiber topology can achieve higher output force per geometric cross-sectional area. Yet, this is not universally true for fluidic artificial muscle bundles, because the contraction and rotation behavior of individual actuator units (fibers) are both key factors contributing to situations where bipennate muscle topologies are advantageous, as compared to parallel muscle topologies. This paper analytically explores the implications of pennation angle on pennate fluidic artificial muscle bundle performance with spatial bounds. A method for muscle bundle parameterization as a function of desired bundle spatial envelope dimensions has been developed. An analysis of actuation performance metrics for bipennate and parallel topologies shows that bipennate artificial muscle bundles can be designed to amplify the muscle contraction, output force, stiffness, or work output capacity, as compared to a parallel bundle with the same envelope dimensions. In addition to quantifying the performance trade space associated with different pennate topologies, analyzing bundles with different fiber boundary conditions reveals how bipennate fluidic artificial muscle bundles can be designed for extensile motion and negative stiffness behaviors. This study, therefore, enables tailoring the muscle bundle parameters for custom compliant actuation applications.more » « less
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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.more » « less
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Lakhtakia, Akhlesh ; Martín-Palma, Raúl J. ; Knez, Mato (Ed.)In this study, the implementation and performance of bipennate topology fluidic artificial muscle (FAM) bundles operating under varying boundary conditions is investigated and quantified experimentally. Soft actuators are of great interest to design engineers due to their inherent flexibility and potential to improve safety in human robot interactions. McKibben fluidic artificial muscles are soft actuators which exhibit high force to weight ratios and dynamically replicate natural muscle movement. These features, in addition to their low fabrication cost, set McKibben FAMs apart as attractive components for an actuation system. Previous studies have shown that there are significant advantages in force and contraction outputs when using bipennate topology FAM bundles as compared to the conventional parallel topology1 . In this study, we will experimentally explore the effects of two possible boundary conditions imposed on FAMs within a bipennate topology. One boundary condition is to pin the muscle fiber ends with fixed pin spacings while the other is biologically inspired and constrains the muscle fibers to remain in contact. This paper will outline design considerations for building a test platform for bipennate fluidic artificial muscle bundles with varying boundary conditions and present experimental results quantifying muscle displacement and force output. These metrics are used to analyze the tradespace between the two boundary conditions and the effect of varying pennation angles.more » « less
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Abstract In this paper, we present a design optimization framework for a fluidic artificial muscle (FAM) bundle subject to geometric constraints. The architecture of natural skeletal muscles allows for compact actuation packaging by distributing a substantial number of actuation elements or muscle fiber motor units, which are to be arranged, oriented, and sized in various formations. Many researchers have drawn inspiration from these natural muscle architectures to assist in designing soft robotic systems safe for human-robot interaction. Although there are known tradeoffs identified between different muscle architectures, this optimization framework offers a method to map these architectural tradeoffs to soft actuator designs. The actuation elements selected for this study are FAMs or McKibben muscles due to their inherent compliance, cheap construction, high force-to-weight ratio, and muscle-like force-contraction behavior. Preceding studies analytically modeled the behavior of arranging FAMs in parallel, asymmetrical unipennate, and symmetrical bipennate topologies inspired by the fiber architectures found in human muscle tissues. A more recent study examined the implications of spatial constraints on bipennate FAM bundle actuation and found that by careful design, a bipennate FAM bundle can produce more force, contraction, stiffness, and work output than that of a parallel FAM bundle under equivalent spatial bounds. This multi-objective genetic algorithm-based optimization framework is used to realize desirable topological properties of a FAM bundle for maximum force and stroke for a given spatial envelope. The results help identify tradeoffs to inform design decisions based on the force and stroke demand from the desired operating task. This study further demonstrates how the desirable topological properties of the optimized FAM bundle change with different spatial bounds.
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