Hierarchical actuator systems

Huston, Dryver R.; Esser, Birgit; Spencer, G.; Burns, Dylan; Kahn, Edward

doi:10.1117/12.607220

Cited by 12 publications

(5 citation statements)

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“…By integrating multiple actuators into a hierarchical configuration, the resulting speed, force, efficiency, stroke and redundancy can be tailored. This approach has proven useful in cellular piezoelectric actuators [1], whiffletree actuators [2], series-parallel approaches [3], and bio-inspired actuator recruitment [4], which utilize multiple small actuators to expand actuator bandwidth and efficiency. Because current mobile robotics applications need energetic improvements [5], hierarchical actuation schemes are of research interest.…”

Section: Introductionmentioning

confidence: 99%

Pennate actuators: force, contraction and stiffness

Jenkins

Bryant²

2020

Bioinspir. Biomim.

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Hierarchical actuators are comprised of multiple individual actuator elements arranged into a system, resulting in improved and expanded performance. Natural muscle tissue is a complex and multi-level example of hierarchical actuation, with its hierarchy spanning from the micrometer to the centimeter scale. In addition to a hierarchical configuration, muscle tissue exists in varying geometric arrangements. Pennate muscle tissue, denoted by its characteristic fibers extending obliquely away from the muscle tissue line of action, leverages geometric complexity to transform the relationship between fiber inputs and muscle tissue outputs. In this paper, a bioinspired hierarchical pennate actuator is detailed. This work expands on previous pennate actuator studies by deriving constitutive force, contraction, and stiffness models for a general pennate actuator, where the constituent fibers can be constructed from any linear actuator. These models are experimentally validated by studying a pennate actuator with McKibben artificial muscles constituting the actuator fibers. McKibben artificial muscles are used because they have a high force-to-weight ratio and are inexpensive to construct, making them an attractive candidate for hierarchical actuators and mobile robotics. Using the derived constitutive models, general pennate actuator performance is better understood by analyzing the transmission ratio, blocked force, and free contraction. Loaded contractions and stiffness during isotonic and isobaric contractions are also explored. The results allow for informed design decisions and an understanding of the associated tradeoffs when recreating the remarkable properties of pennate musculature. Future work will leverage the results of this paper to create an adaptive pennate actuator that is capable of changing configuration in response to force, contraction and stiffness demands.

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Section: Introductionmentioning

confidence: 99%

Pennate actuators: force, contraction and stiffness

Jenkins

Bryant²

2020

Bioinspir. Biomim.

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“…Each motor unit consists of hundred to thousands of muscle fibers that can be arranged in a variety of topologies. Analogously, hierarchical actuators use multi-unit architectures to augment the total actuator performance and increase actuator functionality [2,3]. The practicality of this hierarchical actuation strategy has been demonstrated on cellular piezoelectric actuators [1], whiffletree actuators [2], seriesparallel elastic actuators [4], and bio-inspired orderly recruitment actuator bundles [5].…”

Section: Introductionmentioning

confidence: 99%

“…Analogously, hierarchical actuators use multi-unit architectures to augment the total actuator performance and increase actuator functionality [2,3]. The practicality of this hierarchical actuation strategy has been demonstrated on cellular piezoelectric actuators [1], whiffletree actuators [2], seriesparallel elastic actuators [4], and bio-inspired orderly recruitment actuator bundles [5]. This muscle-inspired hierarchy has led to the development of linear bundle actuators capable of mimicking orderly recruitment, and thus improving efficiency by activating only the smallest required actuator unit for a given task [5][6][7].…”

Section: Introductionmentioning

confidence: 99%

Implications of Spatially Constrained Bipennate Topology on Fluidic Artificial Muscle Bundle Actuation

Duan

Bryant

2022

Actuators

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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.

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“…The activation of motor units to produce a force is called motor unit recruitment and differs markedly from generating an analog signal proportional to the desired force output [11,12]. Actuators with a discrete cellular structure include the work of Dittrich [13], MacNair and Ueda [14] and Huston et al [15]. Both of these works present a type of actuator that is made up of numerous subactuators.…”

Section: Introductionmentioning

confidence: 99%

A muscle-like recruitment actuator with modular redundant actuation units for soft robotics

Mathijssen

Schultz

Vanderborght

et al. 2015

Robotics and Autonomous Systems

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Human muscles contrast sharply with traditional robot actuators in that they consist of several motor units, connected in series and parallel, which can be progressively recruited. Some roboticists have explored this idea in robotic actuators, striving for improvements such as the ability to withstand partial damage, inexpensive repeatability by discrete open loop control and the potential of modular actuators. These systems, however, become rather complex or rely on less widely used actuation techniques such as piezo-actuators or SMAs to produce a compact implementation. This paper presents a novel design of a modular redundant actuation unit which can be combined in various combinations to form compliant actuators with varying characteristics. The actuation unit consists of discretely activated solenoids with an integrated compliant coupling. This paper presents the working principle and the physical implementation in detail. Failure of a single motor unit will merely lead to a loss in performance rather than failure of the actuator. Since each motor unit is discrete, neither power electronics nor control requires analog signals. Isometric experiments display the actuation characteristics and demonstrate the repeatability. The platform can be used in future work to further explore the virtues of exploiting discretization and redundancy in muscle-like control

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Hierarchical actuator systems

Cited by 12 publications

References 0 publications

Pennate actuators: force, contraction and stiffness

Pennate actuators: force, contraction and stiffness

Implications of Spatially Constrained Bipennate Topology on Fluidic Artificial Muscle Bundle Actuation

A muscle-like recruitment actuator with modular redundant actuation units for soft robotics

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