Flow Path Optimization for Soft Pneumatic Actuators: Towards Optimal Performance and Portability

Soft pneumatic actuators (SPAs) are highly desirable for interactive robotics applications owing to their unconventional properties like high compliance, safe human-machine interaction and adaptable design space. The SPA dynamic behaviour is governed by pneumatic supply systems (PSSs) consisting of
source, valve, tubing
and
fittings
. Although their functionality is well known, the inter-dependence of PSS components and their impact on the SPA behaviour has not been quantified, especially in the context of performance and portability. Using the metrics of maximum actuation frequency, air and energy consumption per actuation cycle, here we systematically investigate the effect of five parameters: SPA size, tubing diameter and length, source pressure and valve flow capacity. We model the SPA pressure dynamics model using first principles and define a large study set of 162 model parameter combinations based on commonly used SPAs and PSS components. We then simulate and experimentally measure the maximum actuation frequency in these parameter combinations, while additionally defining experimental protocols for flow characterization of PSS components and valve control strategy for maximizing actuation frequency. Results from experiments and simulations show good agreement, depicting the trends of how different parameters affect SPA performance. An interesting observation was that for a set of SPA size, tubing length and valve flow capacity, there exists a unique optimal tubing diameter that maximizes the actuation frequency. By further analyzing air and energy consumption, this work allows us to define and solve a multi-objective optimization problem to select and control PSS components to optimize SPA performance and portability simultaneously.