Bioinspired passive variable recruitment of fluidic artificial muscles

Abstract

This article presents a novel, passive approach to creating variable actuator recruitment in bundles of fluidic artificial muscles. The passive recruitment control approach is inspired by the functionality of mammalian muscle tissues, in which a single activation signal from the nervous system sequentially triggers contraction of progressively larger actuation elements until the required force is generated. Biologically, this behavior is encoded by differences in electrical resistance properties between smaller and larger muscle-fiber groups. The approach presented here produces analogous behavior using a uniform applied pressure to all fluidic artificial muscles while creating differential pressure responses and threshold pressures among the fluidic artificial muscles via tailored bladder elasticity parameters. A model for using elastic bladder stiffness to control an artificial muscle bundle with a single valve is explored and used to compare a bundle of fluidic artificial muscles with both low and high threshold pressure units to a single fluidic artificial muscle of equivalent displacement and force capability. The results of this analysis indicate the efficacy of using this control method; it is advantageous in cases where a wide range of displacements and forces are necessary and can increase efficiency when the system primarily operates in a low-force regime but requires occasional bursts of high-force capability.

What is an artificial muscle? A comparison of soft actuators to biological muscles

“…Variable recruitment has been studied extensively on McKibbens [106,[279][280][281][282][283][284][285]. As an attempt to mimic the selective recruitment of motor units in a human muscle, a variable recruitment control strategy was implemented using a parallel bundle of miniature McKibben actuators [282].…”

“…This bioinspired control strategy allowed muscle bundles to operate the fewest miniature McKibbes necessary to achieve the desired performance objective, improving the operating efficiency while also increasing force generation and displacement [282]. Additionally, a passive recruitment control approach using McKibben actuators was investigated [283]. This approach used a uniform applied pressure to all McKibbens while creating differential pressure responses and threshold pressures via tailored bladder elasticity parameters.…”

Modeling and analysis of hydraulic piston actuation of McKibben fluidic artificial muscles for hand rehabilitation

“…Soft robots are able to take advantage of the morphology of the body which simplifies the construction of a robotic system (Polygerinos et al, 2015). In exoskeleton applications, soft actuators can often apply force across the biological joint without the need for alignment (Asbeck et al, 2015; Chapman and Bryant, 2018; Tondu and Lopez 2000).…”

“…Although FAMs are traditionally pneumatically activated, the use of hydraulic artificial muscles (HAMs) may greatly improve the overall system efficiency, in comparison with pneumatic FAMs (Tiwari et al, 2012). Hydraulic FAMs have therefore been the subject of a variety of recent studies (Chapman and Bryant, 2018; Focchi et al, 2010; Kothera et al, 2009; Meller et al, 2014).…”

Folded-Tube Soft Pneumatic Actuators for Bending

“…contraction ratio than the individual actuators [3]. Others have looked at how the principles of "variable recruitment" (which is common in mammalian muscle) can be applied to groups of contracting McKibben muscles to achieve gains in efficiency [4]- [8].…”