A Procedure for the Fatigue Life Prediction of Straight Fibers Pneumatic Muscles

Abstract

Different from the McKibben pneumatic muscle actuator, the straight fibers one is made of an elastomeric tube closed at the two ends by two heads that ensure a mechanical and pneumatic seal. High stiffness threads are placed longitudinally into the wall of the tube while external rings are placed at some sections of it to limit the radial expansion of the tube. The inner pressure in the tube causes shortening of the actuator. The working mode of the muscle actuator requires a series of critical repeated contractions and extensions that cause it to rupture. The fatigue life duration of a pneumatic muscle is often lower than traditional pneumatic actuators. The paper presents a procedure for the fatigue life prediction of a straight-fibers muscle based on experimental tests directly carried out with the muscles instead of with specimens of the silicone rubber material which the muscle is made of. The proposed procedure was experimentally validated. Although the procedure is based on fatigue life duration data for silicone rubber, it can be extended to all straight-fibers muscles once the fatigue life duration data of any material considered for the muscles is known.

Two-Dof Upper Limb Rehabilitation Robot Driven by Straight Fibers Pneumatic Muscles

“…As already introduced, it was decided to use the straight fibers pneumatic muscle actuators designed and manufactured by the authors [ 95 , 96 ]. The straight fibers pneumatic muscle consists of a rubber tube with a certain number of threads placed inside the wall in the axial direction.…”

Endurance tests for a fabric_reinforced inflatable soft actuator

“…The Xiameter artificial muscle could reach 229,000 cycles when keeping strains below 50%. A procedure for the fatigue life prediction of a straight fibers pneumatic muscle was introduced by Durante et al (2021). Fatigue life testing was also conducted on swaged pneumatic artificial muscles, which are potential components for aerospace applications in the work of Woods et al (2011).…”

The Research on Soft Pneumatic Actuators in Italy: Design Solutions and Applications

“…A first stress component is tensile stress due to circumferential muscle deformation. The other one is compressive stress, related to the supply pressure, applied between the fiber and the internal surface of the chamber [42]. In some cases, rigid rings divide the muscle into several sectors of equal length to reduce bulge and circumferential stress.…”

“…As well as for MKM, mathematical models have been developed to predic havior of SFM to varying physical (e.g., materials of tube and fibers, number of f [42]. r h , r 0 , l 0 , l f , and s are, respectively, the head radius, the initial radius, the nominal length, the fibers length, and the thickness of the inflatable chamber in resting condition; while l, R and ϕ are the length, the radius of curvature, and the central angle of the deformed inflatable chamber, respectively.…”