Analysis of an anchoring muscle for pipe crawling robot

Pneumatic artificial muscles (PAMs) consist of an elastomeric bladder wrapped in a Kevlar braid. When inflated, PAMs expand radially and contract axially, producing large axial forces. PAMs are often utilized for their high specific work and specific power, as well as their ability to produce large axial displacements. Although the axial behavior of PAMs is well understood, the radial behavior has remained under-utilized and is poorly understood. Radial expansion in large diameter (over 2 inches) PAMs has recently been used in worm-like robots to create anchoring forces that allow for a peristaltic wave which creates locomotion through acrylic pipes. By radially expanding, the PAM presses itself into the pipe, creating an anchor point. The previously anchored PAM then deflates, which propels the robot forward. Modeling of the radial expansion forces and anchoring was desired to determine the pressurization required for proper anchoring before slipping occurs due to the combined robot and payload weight. Modeling was performed using a force balance approach to capture the effects that bladder strain and applied axial load has on the anchoring force. Radial expansion testing was performed to validate the model. Force due to anchoring was recorded using force transducers attached to sections of acrylic pipe using an MTS servo-hydraulic testing machine. Data from the test was compared to the predicted anchoring force.