Design Optimization of a Miniaturized Pneumatic Artificial Muscle and Experimental Validation

Abstract

Miniaturized pneumatic artificial muscles (MPAMs) are widely utilized in various applications due to their unique characteristics, such as a high power-to-weight ratio, flexibility, and compatibility with the human environment, as well as being compact enough to fit within small-scale mechanical systems. Maximizing the amount of force generated by these actuators while keeping their dimensions minimized can greatly affect their efficiency. In this study, a formal design optimization problem was formulated to identify optimal sizes of MPAMs while maximizing their blocked force as a novel approach to address the issue of low force outputs of these actuators. A force model for an MPAM including various correction terms was derived to better predict the response behavior of the actuator. The optimization results reveal that an MPAM with a bladder that has an outer diameter of 6 mm and a thickness of 0.7 mm, as well as a braid angle of 72 degrees, can produce up to almost 239 N of blocked force if the inlet pressure is increased to 600 kPa. An MPAM with optimal parameters was subsequently fabricated and experimentally tested to evaluate its quasi-static response behavior and to validate the theoretical optimization results. Experimental tests were conducted under a wide range of pressures (0–300 kPa) to evaluate the variation of the generated blocked force versus inlet pressure. The overall error between the simulation and the experimental blocked forces was found to be less than 10%. This study represents a significant contribution to the design optimization of MPAMs, and the resulting optimal design offers potential applications in various fields, from soft robots to medical devices.

Development of enhanced force models to analyze the nonlinear hysteresis response of miniaturized pneumatic artificial muscles

“…Poisson's ratio of PET braid, ν s , is nearly 0.33, and the modulus of elasticity of the braid, E br , is typically around 2 GPa. The dimensional parameters (L 0 , t 0 , R 0 , and α 0 ), are initial parameters which may be obtained through design optimization process [24]. Instantaneous parameters (L, R, t, and α) are obtained as described below: Taking into account that B 0 = B and L = L 0 ± ∆L (where ∆L is subtracted from the initial length during contraction and added to it during expansion), the braid angle can be determined at each state as:…”

“…The dimensions of the fabricated MPAMs are presented in table 1, which are determined using the optimized geometrical parameters obtained in our prior study [24], resulting in an improved design of MPAMs with higher force and contraction outputs compared to the other MPAMs of the same dimensions. To fabricate MPAMs with these specified dimensions, customized cylindrical bladders are made using an in-house fabricated 3D-printed mold.…”