Deflected versus preshaped soft pneumatic actuators: A design and performance analysis toward reliable soft robots

Soft pneumatic actuators (SPAs) are customizable and conformable devices that enable desired motions in soft robots. Interactions with the environment or handling during their fabrication could introduce defects into SPAs that affect their performance. These defects could lead to high-stress concentrations in the SPA body and heterogeneous, unrepeatable, or inconsistent expansion affecting their reliability. In this work, we aim to improve the reliability of soft robots by modeling and characterizing the performance of SPAs with widely used chamber shapes and cross-sectional geometries under variable loading conditions. We also compare their capacity to provide homogeneous, repeatable, and time-wise consistent expansion with low-stress concentrations and provide a set of principles for the design of reliable SPAs. Expansion of SPAs with Straight chambers demonstrated to be more repeatable, with an average deviation of 0.06 mm and showed more than a thousand times less stress than any other chamber types. The expansion of preshaped SPAs with helical chambers showed to be up to 500% more homogeneous and 300% more efficient than their deflected counterparts. SPAs with squared cross-sectional geometries displayed more than 1000 times more time-wise consistent expansion over their circular counterparts. We conclude that SPAs that retain less potential energy or are less affected by its effects are more reliable. We derive these results into a set of principles for the design of reliable SPAs. These principles offer solutions to make informed decisions before fabrication to mitigate the most common reliability problems for SPAs and soft robots.