Characterization and application of shape-changing panels with embedded rubber muscle actuators

Abstract

Cylindrical soft actuators efficiently convert fluid pressure into mechanical energy and thus offer excellent force-to-weight ratios while behaving similar to biological muscle. McKibben-like rubber muscle actuators (RMAs) were embedded into neat elastomer and act as shape-changing panels. The effect of actuator spacing and modeling methods on the performance of these panels was investigated. Simulations from nonlinear finite element models were compared with results from test panels containing four RMAs that were spaced 0, 1/2, 1, and 1.3 RMA diameters apart. Nonlinear ‘laminated plate’ and ‘rod & plate’ finite element (FE) models of individual (non-embedded) RMAs and panels with embedded RMAs were developed. Due to model complexity and resource limitations, several simplified 2D and 3D FE model types, including a 3D ‘Unit Cell’ were created. After subtracting the ‘activation pressure’ needed to initiate contraction, all the models for the individual actuators produced forces consistent with experimental values, but only the more resource-intensive rod & plate models replicated fiber/braid re-orientation and produced more realistic values for actuator contraction. For panel models, the Full 3D rod & plate model appeared to be the most accurate for panel contraction and force, but was not completed for all configurations due to resource limitations. Most embedded panel FE models produced maximum panel actuator force and maximum contraction when the embedded actuators are spaced between 1/2 and 1 diameter apart. Seven panels with embedded RMAs were experimentally fabricated and tested. Panel tests confirmed that maximum or optimal performance occurs when the RMAs are spaced between 1/2 and 1 diameter apart. The tested actuator force was fairly constant in this range, suggesting that minor design or manufacturing differences may not significantly affect panel performance. However, the amount of axial force and contraction decreases significantly at greater than optimal spacing. This multi-faceted work provides useful design, simulation fabrication, and test characteristics for shape-adaptive panels. Bending panels were demonstrated but not modeled. Developers of future shape-adaptive air vehicles have been provided with additional simulation and design tools.

Variable Stiffness Structures Utilizing Pneumatic Artificial Muscles

“…In Chen et al's study the transverse stiffness of the morphing skin could be regulated by changing the internal air pressure. Larry et al [8] also fabricated a shape-changing panel with embedded McKibben-like PAMs into neat elastomer. Previously, Feng et al [9] embedded pneumatic muscle fibers into elastomer to form one kind of single-layer morphing skins.…”

Characterizing the Peano fluidic muscle and the effects of its geometry properties on its behavior

“…This is a consequence of their cylindrical cross-section, which results in a significant deadvolume. Multiple narrower PAMs can be configured in parallel for a reduced deadvolume to force ratio [5]. However, these actuators are more complex, with a corresponding decrease in reliability.…”

A bio-inspired, active morphing skin for camber morphing structures

“…Altering the camber of the adaptive airfoil was achieved by employing this kind of active morphing skin. Other than the complex and heavy structure used for variable geometry airfoils in the mission adaptive wing [26], the active morphing skin itself could be used as actuators to change the airfoil chord and camber in this study.…”