Analysis of nonlinear elastic behavior in miniature pneumatic artificial muscles

Abstract

Pneumatic artificial muscles (PAMs) are well known for their excellent actuator characteristics, including high specific work, specific power, and power density. Recent research has focused on miniaturizing this pneumatic actuator technology in order to develop PAMs for use in small-scale mechanical systems, such as those found in robotic or aerospace applications. The first step in implementing these miniature PAMs was to design and characterize the actuator. To that end, this study presents the manufacturing process, experimental characterization, and analytical modeling of PAMs with millimeter-scale diameters. A fabrication method was developed to consistently produce low-cost, high performance, miniature PAMs using commercially available materials. The quasi-static behavior of these PAMs was determined through experimentation on a single actuator with an active length of 39.16 mm (1.54 in) and a diameter of 4.13 mm (0.1625 in). Testing revealed the PAM’s full evolution of force with displacement for operating pressures ranging from 207 to 552 kPa (30–80 psi in 10 psi increments), as well as the blocked force and free contraction at each pressure. Three key nonlinear phenomena were observed: nonlinear PAM stiffness, hysteresis of the force versus displacement response for a given pressure, and a pressure deadband. To address the analysis of the nonlinear response of these miniature PAMs, a nonlinear stress versus strain model, a hysteresis model, and a pressure bias are introduced into a previously developed force balance analysis. Parameters of these nonlinear model refinements are identified from the measured force versus displacement data. This improved nonlinear force balance model is shown to capture the full actuation behavior of the miniature PAMs at each operating pressure and reconstruct miniature PAM response with much more accuracy than previously possible.

Reconsidering the McKibben muscle: Energetics, operating fluid, and bladder material

“…As a result, more complex models have been developed to take into account the shape at the ends of the muscles by including conical segments (Tiwari et al, 2012;Tondu, 2012;Tsagarakis and Caldwell, 2000), while others model the actuator ends as circular arcs (Hocking and Wereley, 2013;Kothera et al, 2009). The results of these experiments show that modeling the muscles presented in this article as cylinders is quite volumetrically accurate.…”

An Integrated Intelligent Nonlinear Control Method for a Pneumatic Artificial Muscle

“…By applying Newton's second law and previous results ( [7], [8], [18], [30]), the force dynamics of the system can be presented under a simple form as 2 2 ( , )…”

“…Remark 1: The spool dynamics of the studied valve are ignored. Based on previous studies [7], [8], [22], [27], [30], it can be seen that the system dynamics (Eqs. (1) - (2)) are not only nonlinear functions of the inputs ( , , )…”

“…In mathematical methods [6]- [8], the static and dynamic characteristics of PAMs were derived from the physical analysis of pressure-force relationships, geometric structure, contraction ratios, elastic characteristics, and viscous and Coulomb frictions. The results showed that the actuators were hard to accurately describe using these models.…”

Fluidic actuation for intra-operative in situ imaging

“…Different PAMs have been designed in the past [14], [18], [19]. In this study McKibben muscles were chosen for their fabrication simplicity and their smaller diameter when actuated, compared to other PAMs, e.g.…”